5. Seamless interoperation with the DOM

5.1. Practical example: a simple, responsive website using no HTML or CSS at all

To many programmers, using ‘static’ HTML and CSS feels like being locked up in a closet. As an alternative, responsiveness can simply be programmed using Transcrypt, as can be seen on the website of Transcrypt itself. The site adapts to diverse screen formats, device types and landscape vs. portrait mode.

5.2. SVG example: Turtle graphics

Turtle graphics are a way to teach computer programming to children, invented by Seymour Papert in the 1960’s. Lines are drawn as ‘track’ of a walking turtle, that can move ahead and turn. Children use turtle graphics intuitively by imagining what they would do if they were the turtle. This leads to a recipe of motion, indeed an algorithm, which is the basis of imperative (as opposed to e.g. declarative) programming.

SVG or Scalable Vector Graphics are a way to display high quality graphs, e.g. in the browser. SVG, as opposed to e.g. the HTML Canvas, bypasses the pixel paradigm and works with floating point coordinates directly. As a consequence, SVG plots can be zoomed without becoming ragged or ‘pixelated’.

When looking under the hood of SVG, there’s an amazing correspondence between the primitives in an SVG path and the primitives of turtle graphics. So both from an aestethical and from a conceptual point of view, turtle graphics and SVG form a happy mariage.

Turtle graphics in Transcrypt do not require the use of any graphics libraries. Below are two turtle graphics examples and the source code of Transcrypt’s turtle module, which is quite compact. As can be seen from the code integration between Transcrypt and JavaScript is trivial.

Drawing a alternatingly floodfilled star

# Free after the example from the Python 3.5 manual

from turtle import *

up ()
goto (-250, -21)
startPos = pos ()

down ()
color ('red', 'yellow')
begin_fill ()
while True:
    forward (500)
    right (170)
    if distance (startPos) < 1:
        break
end_fill ()
done ()

Click here to view the resulting zoomable star.

Drawing the contours of a snowflake

from turtle import *

josh = Turtle ()

def draw (length):
    if length > 9:
        draw (length / 3)
        josh.left (60)
        draw (length / 3)
        josh.right (120)
        draw (length / 3)
        josh.left (60)
        draw (length / 3)
    else:
        josh.forward (length)

length = 150
josh.up ()
josh.forward (length / 2)
josh.left (90)
josh.forward (length / 4)
josh.right (90)
josh.down ()

for i in range (3):
    josh.right (120)
    draw (length)
    
josh.done ()

Click here to view the resulting zoomable snowflake.

Transcrypt’s turtle graphics module sits directly on top of SVG, no libraries needed, so a very compact download

__pragma__ ('skip')
document = Math = setInterval = clearInterval = 0
__pragma__ ('noskip')

_debug = False

#def abs (vec2D):
#    return Math.sqrt (vec2D [0] * vec2D [0] + vec2D [1] * vec2D [1])

_ns = 'http://www.w3.org/2000/svg'
_svg = document.createElementNS (_ns, 'svg')

_defaultElement = document.getElementById ('__turtlegraph__')
if not _defaultElement:
    _defaultElement = document.body
_defaultElement.appendChild (_svg)

_width = None
_height = None
_offset = None

def _rightSize (self):
    nonlocal _width
    nonlocal _height
    nonlocal _offset
    
    _width = _defaultElement.offsetWidth
    _height = _defaultElement.offsetHeight
    _offset = [_width // 2, _height // 2]
    
    _svg.setAttribute ('width', _width)
    _svg.setAttribute ('height', _height)
    
window.onresize = _rightSize

_rightSize ()

def bgcolor (color):
    nonlocal _defaultElement

    _bgcolor = color
    _defaultElement.style.backgroundColor = _bgcolor

bgcolor ('white')
    
def setDefaultElement (element):
    nonlocal _defaultElement

    _defaultElement.removeChild (_svg)
    _defaultElement = element
    element.appendChild (_svg)
    
    _rightSize ()
    bgcolor ('white')

_allTurtles = []
    
class Turtle:
    def __init__ (self):
        _allTurtles.append (self)
        self._paths = []
        self.reset ()
        
    def reset (self):
        self._heading = Math.PI / 2
        self.pensize (1)
        self.color ('black', 'black')
        self.down ()
        self._track = []    # Need to make track explicitly because:
        self.home ()        #   Makes a position but needs a track to put in in
        self.clear ()       #   Makes a track but needs a position to initialize it with
        
    def clear (self):
        for path in self._paths:
            _svg.removeChild (path)
        self._paths = []
        
        self._track = []
        self._moveto (self._position)
        
    def _flush (self):
        if _debug:
            print ('Flush:', self._track)
    
        if len (self._track) > 1:
            path = document.createElementNS (_ns, 'path')
            path.setAttribute ('d', ' '.join (self._track))
            path.setAttribute ('stroke', self._pencolor if self._pencolor != None else 'none')
            path.setAttribute ('stroke-width', self._pensize)
            path.setAttribute ('fill', self._fillcolor if self._fill and self._fillcolor != None else 'none')           
            path.setAttribute ('fill-rule', 'evenodd')
            _svg.appendChild (path)
            self._paths.append (path)
                
            self._track = []
            self._moveto (self._position)   # _track should start with a move command
        
    def done (self):
        self._flush ()
        
    def pensize (self, width):
        self._flush ()
        if width == None:
            return self._pensize
        else:
            self._pensize = width
    
    def color (self, pencolor, fillcolor = None):
        self._flush ()
        self._pencolor = pencolor
        
        if fillcolor != None:
            self._fillcolor = fillcolor
    
    def goto (self, x, y = None):
        if y == None:
            self._position = x
        else:
            self._position = [x, y]
            
        self._track.append ('{} {} {}'.format (
            'L' if self._down else 'M',
            self._position [0] + _offset [0],
            self._position [1] + _offset [1])
        )
        
    def _moveto (self, x, y = None):
        wasdown = self.isdown ()
        self.up ()
        self.goto (x, y)
        if wasdown:
            self.down ()
            
    def home (self):
        self._moveto (0, 0)
        
    def position (self):
        return self._position [:]
        
    def pos (self):
        return self.position ()
        
    def distance (self, x, y = None):
        if y == None:
            other = x
        else:
            other = [x, y]
            
        dX = other [0] - self._position [0]
        dY = other [1] - self._position [1]
        
        return Math.sqrt (dX * dX + dY * dY)
            
    def up (self):
        self._down = False
        
    def down (self):
        self._down = True
        
    def isdown (self):
        return self._down
        
    def _predict (self, length):
        delta = [Math.sin (self._heading), Math.cos (self._heading)]
        return [self._position [0] + length * delta [0], self._position [1] + length * delta [1]]
        
    def forward (self, length):
        self._position = self._predict (length)
        
        self._track.append ('{} {} {}'.format (
            'L' if self._down else 'M',
            self._position [0] + _offset [0],
            self._position [1] + _offset [1])
        )
        
    def back (self, length):
        self.forward (-length)
        
    def circle (self, radius):
        self.left (90)
        opposite = self._predict (2 * (radius + 1) + 1)
        self.right (90)
    
        self._track.append ('{} {} {} {} {} {} {} {}'.format (
            'A',
            radius,
            radius,
            0,
            1,
            0,
            opposite [0] + _offset [0],
            opposite [1] + _offset [1]
        ))
        
        self._track.append ('{} {} {} {} {} {} {} {}'.format (
            'A',
            radius,
            radius,
            0,
            1,
            0,
            self._position [0] + _offset [0],
            self._position [1] + _offset [1]
        ))
        
    def left (self, angle):
        self._heading = (self._heading + Math.PI * angle / 180) % (2 * Math.PI)
            
    def right (self, angle): 
        self.left (-angle)
        
    def begin_fill (self):
        self._flush ()
        self._fill = True
    
    def end_fill (self):
        self._flush ()
        self._fill = False
        
    def speed (speed = None):
        pass
        
_defaultTurtle = Turtle ()
_timer = None
    
def reset ():
    nonlocal _timer, _allTurtles
    if _timer:
        clearTimeout (_timer)
    bgcolor ('white')
    for turtle in _allTurtles:
        turtle.reset ()
        turtle.done ()
        
def clear ():
    nonlocal _allTurtles
    for turtle in _allTurtles:
        turtle.clear ()
        
def ontimer (fun, t = 0):
    nonlocal _timer
    _timer = setTimeout (fun, t)

def done ():                            _defaultTurtle.done ()
def pensize (width):                    _defaultTurtle.pensize (width)
def color (pencolor, fillcolor = None): _defaultTurtle.color (pencolor, fillcolor)
def home ():                            _defaultTurtle.home ()
def goto (x, y = None):                 _defaultTurtle.goto (x, y)
def position ():                        return _defaultTurtle.position ()
def pos ():                             return _defaultTurtle.pos ()
def distance (x, y = None):             return _defaultTurtle.distance (x, y)
def up ():                              _defaultTurtle.up ()
def down ():                            _defaultTurtle.down ()
def forward (length):                   _defaultTurtle.forward (length)
def back (length):                      _defaultTurtle.back (length)
def circle (radius):                    _defaultTurtle.circle (radius)
def left (angle):                       _defaultTurtle.left (angle)
def right (angle):                      _defaultTurtle.right (angle)
def begin_fill ():                      _defaultTurtle.begin_fill ()
def end_fill ():                        _defaultTurtle.end_fill ()
def speed (speed):                      _defaultTurtle.speed (speed)

Remark: In a later stage animation may be added. As a further step, for complicated fractals, transparent server side compilation of a relatively simple algorithm would allow on-line editing combined with fast client side rendering of high-resolution graphics.

6. Mixed examples

6.1. Example: Pong

In using the fabric.js JavaScript library this for example, the only thing differing from plain JavaScript is that new <constructor> is replaced by __new__ (<constructor>).

pong.py __pragma__ ('skip') document = window = Math = Date = 0 # Prevent complaints by optional static checker __pragma__ ('noskip') __pragma__ ('noalias', 'clear') from com.fabricjs import fabric orthoWidth = 1000 orthoHeight = 750 fieldHeight = 650 enter, esc, space = 13, 27, 32 window.onkeydown = lambda event: event.keyCode != space # Prevent scrolldown on spacebar press class Attribute: # Attribute in the gaming sense of the word, rather than of an object def __init__ (self, game): self.game = game # Attribute knows game it's part of self.game.attributes.append (self) # Game knows all its attributes self.install () # Put in place graphical representation of attribute self.reset () # Reset attribute to start position def reset (self): # Restore starting positions or score, then commit to fabric self.commit () # Nothing to restore for the Attribute base class def predict (self): pass def interact (self): pass def commit (self): pass class Sprite (Attribute): # Here, a sprite is an attribute that can move def __init__ (self, game, width, height): self.width = width self.height = height Attribute.__init__ (self, game) def install (self): # The sprite holds an image that fabric can display self.image = __new__ (fabric.Rect ({ 'width': self.game.scaleX (self.width), 'height': self.game.scaleY (self.height), 'originX': 'center', 'originY': 'center', 'fill': 'white' })) __pragma__ ('kwargs') def reset (self, vX = 0, vY = 0, x = 0, y = 0): self.vX = vX # Speed self.vY = vY self.x = x # Predicted position, can be commit, no bouncing initially self.y = y Attribute.reset (self) __pragma__ ('nokwargs') def predict (self): # Predict position, do not yet commit, bouncing may alter it self.x += self.vX * self.game.deltaT self.y += self.vY * self.game.deltaT def commit (self): # Update fabric image for asynch draw self.image.left = self.game.orthoX (self.x) self.image.top = self.game.orthoY (self.y) def draw (self): self.game.canvas.add (self.image) class Paddle (Sprite): margin = 30 # Distance of paddles from walls width = 10 height = 100 speed = 400 # / s def __init__ (self, game, index): self.index = index # Paddle knows its player index, 0 == left, 1 == right Sprite.__init__ (self, game, self.width, self.height) def reset (self): # Put paddle in rest position, dependent on player index Sprite.reset ( self, x = orthoWidth // 2 - self.margin if self.index else -orthoWidth // 2 + self.margin, y = 0 ) def predict (self): # Let paddle react on keys self.vY = 0 if self.index: # Right player if self.game.keyCode == ord ('K'): # Letter K pressed self.vY = self.speed elif self.game.keyCode == ord ('M'): self.vY = -self.speed else: # Left player if self.game.keyCode == ord ('A'): self.vY = self.speed elif self.game.keyCode == ord ('Z'): self.vY = -self.speed Sprite.predict (self) # Do not yet commit, paddle may bounce with walls def interact (self): # Paddles and ball assumed infinitely thin # Paddle touches wall self.y = Math.max (self.height // 2 - fieldHeight // 2, Math.min (self.y, fieldHeight // 2 - self.height // 2)) # Paddle hits ball if ( (self.y - self.height // 2) < self.game.ball.y < (self.y + self.height // 2) and ( (self.index == 0 and self.game.ball.x < self.x) # On or behind left paddle or (self.index == 1 and self.game.ball.x > self.x) # On or behind right paddle ) ): self.game.ball.x = self.x # Ball may have gone too far already self.game.ball.vX = -self.game.ball.vX # Bounce on paddle self.game.ball.speedUp (self) class Ball (Sprite): side = 8 speed = 300 # / s def __init__ (self, game): Sprite.__init__ (self, game, self.side, self.side) def reset (self): # Launch according to service direction with random angle offset from horizontal angle = ( self.game.serviceIndex * Math.PI # Service direction + (1 if Math.random () > 0.5 else -1) * Math.random () * Math.atan (fieldHeight / orthoWidth) ) Sprite.reset ( self, vX = self.speed * Math.cos (angle), vY = self.speed * Math.sin (angle) ) def predict (self): Sprite.predict (self) # Integrate velocity to position if self.x < -orthoWidth // 2: # If out on left side self.game.scored (1) # Right player scored elif self.x > orthoWidth // 2: self.game.scored (0) if self.y > fieldHeight // 2: # If it hits top wall self.y = fieldHeight // 2 # It may have gone too far already self.vY = -self.vY # Bounce elif self.y < -fieldHeight // 2: self.y = -fieldHeight // 2 self.vY = -self.vY def speedUp (self, bat): factor = 1 + 0.15 * (1 - Math.abs (self.y - bat.y) / (bat.height // 2)) ** 2 # Speed will increase more if paddle hit near centre if Math.abs (self.vX) < 3 * self.speed: self.vX *= factor self.vY *= factor class Scoreboard (Attribute): nameShift = 75 hintShift = 25 def install (self): # Graphical representation of scoreboard are four labels and a separator line self.playerLabels = [__new__ (fabric.Text ('Player {}'.format (name), { 'fill': 'white', 'fontFamily': 'arial', 'fontSize': '{}' .format (self.game.canvas.width / 30), 'left': self.game.orthoX (position * orthoWidth), 'top': self.game.orthoY (fieldHeight // 2 + self.nameShift) })) for name, position in (('AZ keys:', -7/16), ('KM keys:', 1/16))] self.hintLabel = __new__ (fabric.Text ('[spacebar] starts game, [enter] resets score', { 'fill': 'white', 'fontFamily': 'arial', 'fontSize': '{}'.format (self.game.canvas.width / 70), 'left': self.game.orthoX (-7/16 * orthoWidth), 'top': self.game.orthoY (fieldHeight // 2 + self.hintShift) })) self.image = __new__ (fabric.Line ([ self.game.orthoX (-orthoWidth // 2), self.game.orthoY (fieldHeight // 2), self.game.orthoX (orthoWidth // 2), self.game.orthoY (fieldHeight // 2) ], {'stroke': 'white'} )) def increment (self, playerIndex): self.scores [playerIndex] += 1 def reset (self): self.scores = [0, 0] Attribute.reset (self) # Only does a commit here def commit (self): # Committing labels is adapting their texts self.scoreLabels = [__new__ (fabric.Text ('{}'.format (score), { 'fill': 'white', 'fontFamily': 'arial', 'fontSize': '{}'.format (self.game.canvas.width / 30), 'left': self.game.orthoX (position * orthoWidth), 'top': self.game.orthoY (fieldHeight // 2 + self.nameShift) })) for score, position in zip (self.scores, (-2/16, 6/16))] def draw (self): for playerLabel, scoreLabel in zip (self.playerLabels, self.scoreLabels): self.game.canvas.add (playerLabel) self.game.canvas.add (scoreLabel) self.game.canvas.add (self.hintLabel) self.game.canvas.add (self.image) class Game: def __init__ (self): self.serviceIndex = 1 if Math.random () > 0.5 else 0 # Index of player that has initial service self.pause = True # Start game in paused state self.keyCode = None self.textFrame = document.getElementById ('text_frame') self.canvasFrame = document.getElementById ('canvas_frame') self.buttonsFrame = document.getElementById ('buttons_frame') self.canvas = __new__ (fabric.Canvas ('canvas', {'backgroundColor': 'black', 'originX': 'center', 'originY': 'center'})) self.canvas.onWindowDraw = self.draw # Install draw callback, will be called asynch self.canvas.lineWidth = 2 self.canvas.clear () self.attributes = [] # All attributes will insert themselves here self.paddles = [Paddle (self, index) for index in range (2)] # Pass game as parameter self self.ball = Ball (self) self.scoreboard = Scoreboard (self) window.setInterval (self.update, 10) # Install update callback, time in ms window.setInterval (self.draw, 20) # Install draw callback, time in ms window.addEventListener ('keydown', self.keydown) window.addEventListener ('keyup', self.keyup) self.buttons = [] for key in ('A', 'Z', 'K', 'M', 'space', 'enter'): button = document.getElementById (key) button.addEventListener ('mousedown', (lambda aKey: lambda: self.mouseOrTouch (aKey, True)) (key)) # Returns inner lambda button.addEventListener ('touchstart', (lambda aKey: lambda: self.mouseOrTouch (aKey, True)) (key)) button.addEventListener ('mouseup', (lambda aKey: lambda: self.mouseOrTouch (aKey, False)) (key)) button.addEventListener ('touchend', (lambda aKey: lambda: self.mouseOrTouch (aKey, False)) (key)) button.style.cursor = 'pointer' button.style.userSelect = 'none' self.buttons.append (button) self.time = + __new__ (Date) window.onresize = self.resize self.resize () def install (self): for attribute in self.attributes: attribute.install () def mouseOrTouch (self, key, down): if down: if key == 'space': self.keyCode = space elif key == 'enter': self.keyCode = enter else: self.keyCode = ord (key) else: self.keyCode = None def update (self): # Note that update and draw are not synchronized oldTime = self.time self.time = + __new__ (Date) self.deltaT = (self.time - oldTime) / 1000. if self.pause: # If in paused state if self.keyCode == space: # If spacebar hit self.pause = False # Start playing elif self.keyCode == enter: # Else if enter hit self.scoreboard.reset () # Reset score else: # Else, so if in active state for attribute in self.attributes: # Compute predicted values attribute.predict () for attribute in self.attributes: # Correct values for bouncing and scoring attribute.interact () for attribute in self.attributes: # Commit them to pyglet for display attribute.commit () def scored (self, playerIndex): # Player has scored self.scoreboard.increment (playerIndex) # Increment player's points self.serviceIndex = 1 - playerIndex # Grant service to the unlucky player for paddle in self.paddles: # Put paddles in rest position paddle.reset () self.ball.reset () # Put ball in rest position self.pause = True # Wait for next round def commit (self): for attribute in self.attributes: attribute.commit () def draw (self): self.canvas.clear () for attribute in self.attributes: attribute.draw () def resize (self): self.pageWidth = window.innerWidth self.pageHeight = window.innerHeight self.textTop = 0 if self.pageHeight > 1.2 * self.pageWidth: self.canvasWidth = self.pageWidth self.canvasTop = self.textTop + 300 else: self.canvasWidth = 0.6 * self.pageWidth self.canvasTop = self.textTop + 200 self.canvasLeft = 0.5 * (self.pageWidth - self.canvasWidth) self.canvasHeight = 0.6 * self.canvasWidth self.buttonsTop = self.canvasTop + self.canvasHeight + 50 self.buttonsWidth = 500 self.textFrame.style.top = self.textTop; self.textFrame.style.left = self.canvasLeft + 0.05 * self.canvasWidth self.textFrame.style.width = 0.9 * self.canvasWidth self.canvasFrame.style.top = self.canvasTop self.canvasFrame.style.left = self.canvasLeft self.canvas.setDimensions ({'width': self.canvasWidth, 'height': self.canvasHeight}) self.buttonsFrame.style.top = self.buttonsTop self.buttonsFrame.style.left = 0.5 * (self.pageWidth - self.buttonsWidth) self.buttonsFrame.style.width = self.canvasWidth self.install () self.commit () self.draw () def scaleX (self, x): return x * (self.canvas.width / orthoWidth) def scaleY (self, y): return y * (self.canvas.height / orthoHeight) def orthoX (self, x): return self.scaleX (x + orthoWidth // 2) def orthoY (self, y): return self.scaleY (orthoHeight - fieldHeight // 2 - y) def keydown (self, event): self.keyCode = event.keyCode def keyup (self, event): self.keyCode = None game = Game () # Create and run game

pong.js // Transcrypt'ed from Python, 2023-04-22 17:11:43 import {AssertionError, AttributeError, BaseException, DeprecationWarning, Exception, IndexError, IterableError, KeyError, NotImplementedError, RuntimeWarning, StopIteration, UserWarning, ValueError, Warning, __JsIterator__, __PyIterator__, __Terminal__, __add__, __and__, __call__, __class__, __envir__, __eq__, __floordiv__, __ge__, __get__, __getcm__, __getitem__, __getslice__, __getsm__, __gt__, __i__, __iadd__, __iand__, __idiv__, __ijsmod__, __ilshift__, __imatmul__, __imod__, __imul__, __in__, __init__, __ior__, __ipow__, __irshift__, __isub__, __ixor__, __jsUsePyNext__, __jsmod__, __k__, __kwargtrans__, __le__, __lshift__, __lt__, __matmul__, __mergefields__, __mergekwargtrans__, __mod__, __mul__, __ne__, __neg__, __nest__, __or__, __pow__, __pragma__, __pyUseJsNext__, __rshift__, __setitem__, __setproperty__, __setslice__, __sort__, __specialattrib__, __sub__, __super__, __t__, __terminal__, __truediv__, __withblock__, __xor__, abs, all, any, assert, bool, bytearray, bytes, callable, chr, copy, deepcopy, delattr, dict, dir, divmod, enumerate, filter, float, format, getattr, hasattr, input, int, isinstance, issubclass, len, list, map, max, min, object, ord, pow, print, property, py_TypeError, py_iter, py_metatype, py_next, py_reversed, py_typeof, range, repr, round, set, setattr, sorted, str, sum, tuple, zip} from './org.transcrypt.__runtime__.js'; import {fabric} from './com.fabricjs.js'; var __name__ = '__main__'; export var orthoWidth = 1000; export var orthoHeight = 750; export var fieldHeight = 650; var __left0__ = tuple ([13, 27, 32]); export var enter = __left0__ [0]; export var esc = __left0__ [1]; export var space = __left0__ [2]; window.onkeydown = (function __lambda__ (event) { return event.keyCode != space; }); export var Attribute = __class__ ('Attribute', [object], { __module__: __name__, get __init__ () {return __get__ (this, function (self, game) { self.game = game; self.game.attributes.append (self); self.install (); self.reset (); });}, get reset () {return __get__ (this, function (self) { self.commit (); });}, get predict () {return __get__ (this, function (self) { // pass; });}, get interact () {return __get__ (this, function (self) { // pass; });}, get commit () {return __get__ (this, function (self) { // pass; });} }); export var Sprite = __class__ ('Sprite', [Attribute], { __module__: __name__, get __init__ () {return __get__ (this, function (self, game, width, height) { self.width = width; self.height = height; Attribute.__init__ (self, game); });}, get install () {return __get__ (this, function (self) { self.image = new fabric.Rect (dict ({'width': self.game.scaleX (self.width), 'height': self.game.scaleY (self.height), 'originX': 'center', 'originY': 'center', 'fill': 'white'})); });}, get reset () {return __get__ (this, function (self, vX, vY, x, y) { if (typeof vX == 'undefined' || (vX != null && vX.hasOwnProperty ("__kwargtrans__"))) {; var vX = 0; }; if (typeof vY == 'undefined' || (vY != null && vY.hasOwnProperty ("__kwargtrans__"))) {; var vY = 0; }; if (typeof x == 'undefined' || (x != null && x.hasOwnProperty ("__kwargtrans__"))) {; var x = 0; }; if (typeof y == 'undefined' || (y != null && y.hasOwnProperty ("__kwargtrans__"))) {; var y = 0; }; if (arguments.length) { var __ilastarg0__ = arguments.length - 1; if (arguments [__ilastarg0__] && arguments [__ilastarg0__].hasOwnProperty ("__kwargtrans__")) { var __allkwargs0__ = arguments [__ilastarg0__--]; for (var __attrib0__ in __allkwargs0__) { switch (__attrib0__) { case 'self': var self = __allkwargs0__ [__attrib0__]; break; case 'vX': var vX = __allkwargs0__ [__attrib0__]; break; case 'vY': var vY = __allkwargs0__ [__attrib0__]; break; case 'x': var x = __allkwargs0__ [__attrib0__]; break; case 'y': var y = __allkwargs0__ [__attrib0__]; break; } } } } else { } self.vX = vX; self.vY = vY; self.x = x; self.y = y; Attribute.reset (self); });}, get predict () {return __get__ (this, function (self) { self.x += self.vX * self.game.deltaT; self.y += self.vY * self.game.deltaT; });}, get commit () {return __get__ (this, function (self) { self.image.left = self.game.orthoX (self.x); self.image.top = self.game.orthoY (self.y); });}, get draw () {return __get__ (this, function (self) { self.game.canvas.add (self.image); });} }); export var Paddle = __class__ ('Paddle', [Sprite], { __module__: __name__, margin: 30, width: 10, height: 100, speed: 400, get __init__ () {return __get__ (this, function (self, game, index) { self.index = index; Sprite.__init__ (self, game, self.width, self.height); });}, get reset () {return __get__ (this, function (self) { Sprite.reset (self, __kwargtrans__ ({x: (self.index ? Math.floor (orthoWidth / 2) - self.margin : Math.floor (-(orthoWidth) / 2) + self.margin), y: 0})); });}, get predict () {return __get__ (this, function (self) { self.vY = 0; if (self.index) { if (self.game.keyCode == ord ('K')) { self.vY = self.speed; } else if (self.game.keyCode == ord ('M')) { self.vY = -(self.speed); } } else if (self.game.keyCode == ord ('A')) { self.vY = self.speed; } else if (self.game.keyCode == ord ('Z')) { self.vY = -(self.speed); } Sprite.predict (self); });}, get interact () {return __get__ (this, function (self) { self.y = Math.max (Math.floor (self.height / 2) - Math.floor (fieldHeight / 2), Math.min (self.y, Math.floor (fieldHeight / 2) - Math.floor (self.height / 2))); if ((self.y - Math.floor (self.height / 2) < self.game.ball.y && self.game.ball.y < self.y + Math.floor (self.height / 2)) && (self.index == 0 && self.game.ball.x < self.x || self.index == 1 && self.game.ball.x > self.x)) { self.game.ball.x = self.x; self.game.ball.vX = -(self.game.ball.vX); self.game.ball.speedUp (self); } });} }); export var Ball = __class__ ('Ball', [Sprite], { __module__: __name__, side: 8, speed: 300, get __init__ () {return __get__ (this, function (self, game) { Sprite.__init__ (self, game, self.side, self.side); });}, get reset () {return __get__ (this, function (self) { var angle = self.game.serviceIndex * Math.PI + ((Math.random () > 0.5 ? 1 : -(1)) * Math.random ()) * Math.atan (fieldHeight / orthoWidth); Sprite.reset (self, __kwargtrans__ ({vX: self.speed * Math.cos (angle), vY: self.speed * Math.sin (angle)})); });}, get predict () {return __get__ (this, function (self) { Sprite.predict (self); if (self.x < Math.floor (-(orthoWidth) / 2)) { self.game.scored (1); } else if (self.x > Math.floor (orthoWidth / 2)) { self.game.scored (0); } if (self.y > Math.floor (fieldHeight / 2)) { self.y = Math.floor (fieldHeight / 2); self.vY = -(self.vY); } else if (self.y < Math.floor (-(fieldHeight) / 2)) { self.y = Math.floor (-(fieldHeight) / 2); self.vY = -(self.vY); } });}, get speedUp () {return __get__ (this, function (self, bat) { var factor = 1 + 0.15 * Math.pow (1 - Math.abs (self.y - bat.y) / (Math.floor (bat.height / 2)), 2); if (Math.abs (self.vX) < 3 * self.speed) { self.vX *= factor; self.vY *= factor; } });} }); export var Scoreboard = __class__ ('Scoreboard', [Attribute], { __module__: __name__, nameShift: 75, hintShift: 25, get install () {return __get__ (this, function (self) { self.playerLabels = (function () { var __accu0__ = []; for (var [py_name, position] of tuple ([tuple (['AZ keys:', -(7) / 16]), tuple (['KM keys:', 1 / 16])])) { __accu0__.append (new fabric.Text ('Player {}'.format (py_name), dict ({'fill': 'white', 'fontFamily': 'arial', 'fontSize': '{}'.format (self.game.canvas.width / 30), 'left': self.game.orthoX (position * orthoWidth), 'top': self.game.orthoY (Math.floor (fieldHeight / 2) + self.nameShift)}))); } return __accu0__; }) (); self.hintLabel = new fabric.Text ('[spacebar] starts game, [enter] resets score', dict ({'fill': 'white', 'fontFamily': 'arial', 'fontSize': '{}'.format (self.game.canvas.width / 70), 'left': self.game.orthoX ((-(7) / 16) * orthoWidth), 'top': self.game.orthoY (Math.floor (fieldHeight / 2) + self.hintShift)})); self.image = new fabric.Line ([self.game.orthoX (Math.floor (-(orthoWidth) / 2)), self.game.orthoY (Math.floor (fieldHeight / 2)), self.game.orthoX (Math.floor (orthoWidth / 2)), self.game.orthoY (Math.floor (fieldHeight / 2))], dict ({'stroke': 'white'})); });}, get increment () {return __get__ (this, function (self, playerIndex) { self.scores [playerIndex]++; });}, get reset () {return __get__ (this, function (self) { self.scores = [0, 0]; Attribute.reset (self); });}, get commit () {return __get__ (this, function (self) { self.scoreLabels = (function () { var __accu0__ = []; for (var [score, position] of zip (self.scores, tuple ([-(2) / 16, 6 / 16]))) { __accu0__.append (new fabric.Text ('{}'.format (score), dict ({'fill': 'white', 'fontFamily': 'arial', 'fontSize': '{}'.format (self.game.canvas.width / 30), 'left': self.game.orthoX (position * orthoWidth), 'top': self.game.orthoY (Math.floor (fieldHeight / 2) + self.nameShift)}))); } return __accu0__; }) (); });}, get draw () {return __get__ (this, function (self) { for (var [playerLabel, scoreLabel] of zip (self.playerLabels, self.scoreLabels)) { self.game.canvas.add (playerLabel); self.game.canvas.add (scoreLabel); self.game.canvas.add (self.hintLabel); } self.game.canvas.add (self.image); });} }); export var Game = __class__ ('Game', [object], { __module__: __name__, get __init__ () {return __get__ (this, function (self) { self.serviceIndex = (Math.random () > 0.5 ? 1 : 0); self.pause = true; self.keyCode = null; self.textFrame = document.getElementById ('text_frame'); self.canvasFrame = document.getElementById ('canvas_frame'); self.buttonsFrame = document.getElementById ('buttons_frame'); self.canvas = new fabric.Canvas ('canvas', dict ({'backgroundColor': 'black', 'originX': 'center', 'originY': 'center'})); self.canvas.onWindowDraw = self.draw; self.canvas.lineWidth = 2; self.canvas.clear (); self.attributes = []; self.paddles = (function () { var __accu0__ = []; for (var index = 0; index < 2; index++) { __accu0__.append (Paddle (self, index)); } return __accu0__; }) (); self.ball = Ball (self); self.scoreboard = Scoreboard (self); window.setInterval (self.py_update, 10); window.setInterval (self.draw, 20); window.addEventListener ('keydown', self.keydown); window.addEventListener ('keyup', self.keyup); self.buttons = []; for (var key of tuple (['A', 'Z', 'K', 'M', 'space', 'enter'])) { var button = document.getElementById (key); button.addEventListener ('mousedown', (function __lambda__ (aKey) { return (function __lambda__ () { return self.mouseOrTouch (aKey, true); }); }) (key)); button.addEventListener ('touchstart', (function __lambda__ (aKey) { return (function __lambda__ () { return self.mouseOrTouch (aKey, true); }); }) (key)); button.addEventListener ('mouseup', (function __lambda__ (aKey) { return (function __lambda__ () { return self.mouseOrTouch (aKey, false); }); }) (key)); button.addEventListener ('touchend', (function __lambda__ (aKey) { return (function __lambda__ () { return self.mouseOrTouch (aKey, false); }); }) (key)); button.style.cursor = 'pointer'; button.style.userSelect = 'none'; self.buttons.append (button); } self.time = +(new Date); window.onresize = self.resize; self.resize (); });}, get install () {return __get__ (this, function (self) { for (var attribute of self.attributes) { attribute.install (); } });}, get mouseOrTouch () {return __get__ (this, function (self, key, down) { if (down) { if (key == 'space') { self.keyCode = space; } else if (key == 'enter') { self.keyCode = enter; } else { self.keyCode = ord (key); } } else { self.keyCode = null; } });}, get py_update () {return __get__ (this, function (self) { var oldTime = self.time; self.time = +(new Date); self.deltaT = (self.time - oldTime) / 1000.0; if (self.pause) { if (self.keyCode == space) { self.pause = false; } else if (self.keyCode == enter) { self.scoreboard.reset (); } } else { for (var attribute of self.attributes) { attribute.predict (); } for (var attribute of self.attributes) { attribute.interact (); } for (var attribute of self.attributes) { attribute.commit (); } } });}, get scored () {return __get__ (this, function (self, playerIndex) { self.scoreboard.increment (playerIndex); self.serviceIndex = 1 - playerIndex; for (var paddle of self.paddles) { paddle.reset (); } self.ball.reset (); self.pause = true; });}, get commit () {return __get__ (this, function (self) { for (var attribute of self.attributes) { attribute.commit (); } });}, get draw () {return __get__ (this, function (self) { self.canvas.clear (); for (var attribute of self.attributes) { attribute.draw (); } });}, get resize () {return __get__ (this, function (self) { self.pageWidth = window.innerWidth; self.pageHeight = window.innerHeight; self.textTop = 0; if (self.pageHeight > 1.2 * self.pageWidth) { self.canvasWidth = self.pageWidth; self.canvasTop = self.textTop + 300; } else { self.canvasWidth = 0.6 * self.pageWidth; self.canvasTop = self.textTop + 200; } self.canvasLeft = 0.5 * (self.pageWidth - self.canvasWidth); self.canvasHeight = 0.6 * self.canvasWidth; self.buttonsTop = (self.canvasTop + self.canvasHeight) + 50; self.buttonsWidth = 500; self.textFrame.style.top = self.textTop; self.textFrame.style.left = self.canvasLeft + 0.05 * self.canvasWidth; self.textFrame.style.width = 0.9 * self.canvasWidth; self.canvasFrame.style.top = self.canvasTop; self.canvasFrame.style.left = self.canvasLeft; self.canvas.setDimensions (dict ({'width': self.canvasWidth, 'height': self.canvasHeight})); self.buttonsFrame.style.top = self.buttonsTop; self.buttonsFrame.style.left = 0.5 * (self.pageWidth - self.buttonsWidth); self.buttonsFrame.style.width = self.canvasWidth; self.install (); self.commit (); self.draw (); });}, get scaleX () {return __get__ (this, function (self, x) { return x * (self.canvas.width / orthoWidth); });}, get scaleY () {return __get__ (this, function (self, y) { return y * (self.canvas.height / orthoHeight); });}, get orthoX () {return __get__ (this, function (self, x) { return self.scaleX (x + Math.floor (orthoWidth / 2)); });}, get orthoY () {return __get__ (this, function (self, y) { return self.scaleY ((orthoHeight - Math.floor (fieldHeight / 2)) - y); });}, get keydown () {return __get__ (this, function (self, event) { self.keyCode = event.keyCode; });}, get keyup () {return __get__ (this, function (self, event) { self.keyCode = null; });} }); export var game = Game (); //# sourceMappingURL=pong.map

6.1.1. Four ways of integration with JavaScript libraries

There are four ways to integrate Transcrypt applications with existing JavaScript libraries.

1. The simplest way is to use the library as is, without any encapsulation. In this way all symbols of that library will be in the global namespace. While many JavaScript programmers don’t seem to mind that, many Python programmers do. For example, in the Terminal demo, the JavaScript module is imported using a <script> tag in the HTML header:

terminal_demo.html

<html>
    <head>
        <script type="module">import * as terminal_demo from "./__target__/terminal_demo.js";</script>
    </head>
    <body>
        <div id='__terminal__'></div>
    </body>
</html>

2. Another way is to encapsulate the JavaScript library as a whole in a Transcrypt module. In the distribution this is done for the fabric module, that encapsulates fabric.js and is imported in the Pong example. In this way the global namespace stays clean.

3. A third way is to write a complete Pythonic API for the JavaScript library. This is overkill in most cases and makes it harder to keep up with new versions of the library. Note that Transcrypt was designed to make seamless cooperation between Transcrypt and JavaScript libraries possible without any glue code.

4. The fourth way is one of the most convenient, but it only works if you are using something like Webpack or Parcel to process and bundle the JavaScript files. In that case, you can use the Node require() function to dynamically load JavaScript libraries into the namespace.

nodejs_demo.py

import time

http = require ('http')

class Demo:
    def __init__ (self, port):
        print ('Demo server started on port', port)
        self.server = http.createServer (self.serve)
        self.server.listen (port)
        self.oldIndex = 0
        self.newIndex = 0
        self.count = 0

In most cases, approach 2 strikes a good balance between effort and yield. As can be seen below, the effort involved is minimal.

The encapsulation layer for fabric.js

__pragma__ ('noanno')

fabric = __pragma__ ('js',
    '''
(function () {{
    var exports = {{}};
    {}  // Puts fabric in exports and in global window
    delete window.fabric;
    return exports;
}}) () .fabric;
    ''',
    __include__ ('com/fabricjs/fabric_downloaded.js')
)

Note that __pragma__ (‘js’, <skeletoncode>, includes = [<file1>, <file2>, ..]) is used to achieve the encapsulation. It replaces the {} by the respective contents of the files. The fabric module is part of the download. Note that not all facilities were included in customizing fabric.js. You can drop-in replace the fabric.js by another customized version without changing anything. Preferably download a development version, since that enables easy debugging. Transcrypt will minify it for you on the fly.

6.1.2. Minification

Minification is currently performed by the Google closure compiler, that’s also part of the distribution. Currently closures ADVANCED_OPTIMIZATIONS switch breaks the working strict code, however, so the SIMPLE_OPTIMIZATIONS switch is used by default.

As can be seen from the listings of the Pong example, even the non-minified pong.js module is only slightly larger than pong.py. This is despite the expensive keyword arguments mechanism that is activated for the reset function, using __pragma__ (‘kwargs’) and __pragma__ (‘nokwargs’). The minified but not treeshaked Transcrypt runtime is slightly above 40 kB. The fabric.js library on the other hand occupies 180 kB. From this example it becomes clear that Transcrypt is extremely lightweight.

6.2. Example: jQuery

In contrast to the use of the fabric.js library in the Pong example, jQuery hasn’t been encapsulated at all. It’s just downloaded on the fly from a content delivery network and used as-is. Instead of the $ (that is not a valid Python identifier), an S is used as alias. This might have been any character sequence.

jquery_demo.py __pragma__ ('alias', 'S', '$') def start (): def changeColors (): for div in S__divs: S (div) .css ({ 'color': 'rgb({},{},{})'.format (* [int (256 * Math.random ()) for i in range (3)]), }) S__divs = S ('div') changeColors () window.setInterval (changeColors, 500)

jquery_demo.js // Transcrypt'ed from Python, 2023-04-22 17:10:57 import {AssertionError, AttributeError, BaseException, DeprecationWarning, Exception, IndexError, IterableError, KeyError, NotImplementedError, RuntimeWarning, StopIteration, UserWarning, ValueError, Warning, __JsIterator__, __PyIterator__, __Terminal__, __add__, __and__, __call__, __class__, __envir__, __eq__, __floordiv__, __ge__, __get__, __getcm__, __getitem__, __getslice__, __getsm__, __gt__, __i__, __iadd__, __iand__, __idiv__, __ijsmod__, __ilshift__, __imatmul__, __imod__, __imul__, __in__, __init__, __ior__, __ipow__, __irshift__, __isub__, __ixor__, __jsUsePyNext__, __jsmod__, __k__, __kwargtrans__, __le__, __lshift__, __lt__, __matmul__, __mergefields__, __mergekwargtrans__, __mod__, __mul__, __ne__, __neg__, __nest__, __or__, __pow__, __pragma__, __pyUseJsNext__, __rshift__, __setitem__, __setproperty__, __setslice__, __sort__, __specialattrib__, __sub__, __super__, __t__, __terminal__, __truediv__, __withblock__, __xor__, abs, all, any, assert, bool, bytearray, bytes, callable, chr, copy, deepcopy, delattr, dict, dir, divmod, enumerate, filter, float, format, getattr, hasattr, input, int, isinstance, issubclass, len, list, map, max, min, object, ord, pow, print, property, py_TypeError, py_iter, py_metatype, py_next, py_reversed, py_typeof, range, repr, round, set, setattr, sorted, str, sum, tuple, zip} from './org.transcrypt.__runtime__.js'; var __name__ = '__main__'; export var start = function () { var changeColors = function () { for (var div of $divs) { $ (div).css (dict ({'color': 'rgb({},{},{})'.format (...(function () { var __accu0__ = []; for (var i = 0; i < 3; i++) { __accu0__.append (int (256 * Math.random ())); } return __accu0__; }) ())})); } }; var $divs = $ ('div'); changeColors (); window.setInterval (changeColors, 500); }; //# sourceMappingURL=jquery_demo.map

6.3. Example: iOS web app with native look and feel

You can write full screen iOS web apps in Transcrypt with native look and feel. As example here’s an app simulating 6 dice. While this example is kept very simple, you can in fact make apps of arbitrary complexity, with fast and beautiful graphics using any JS graphics library, e.g. multiplayer games working over the Internet. If you add the app to your homescreen it will be cached, so no Internet connection is needed to use it. Web apps for iOS can obtain and use location information from the user.

You can install this app on your iPhone from http://www.transcrypt.org/live/transcrypt/demos/ios_app/ios_app.html .

ios_app.py import random class Dice: def __init__ (self): document.body.addEventListener ('touchstart', lambda event: event.preventDefault ()) document.body.addEventListener ('mousedown', lambda event: event.preventDefault ()) document.body.style.margin = 0 document.body.style.overflow = 'hidden'; self.all = document.createElement ('div') self.all.style.color = 'white' self.all.style.backgroundColor = 'black' self.all.style.height = '100%' self.all.style.width = '100%' self.all.style.padding = 0 self.all.style.margin = 0 document.body.appendChild (self.all) self.dices = [] for index in range (6): dice = document.createElement ('div') dice.normalColor = '#770000' if index < 3 else '#0000ff' dice.style.position = 'absolute' dice.style.backgroundColor = dice.normalColor dice.addEventListener ('touchstart', (lambda aDice: lambda: self.roll (aDice)) (dice)) # Returns inner lambda dice.addEventListener ('mousedown', (lambda aDice: lambda: self.roll (aDice)) (dice)) self.dices.append (dice) self.all.appendChild (dice) dice.inner = document.createElement ('div') dice.inner.setAttribute ('unselectable', 'on') dice.inner.style.fontWeight = 'bold' dice.inner.style.textAlign = 'center' dice.inner.style.position = 'absolute' dice.inner.innerHTML = '?' dice.appendChild (dice.inner) self.banner = document.createElement ('div') self.banner.style.position = 'absolute' self.banner.style.cursor = 'pointer' self.banner.addEventListener ('touchstart', self.gotoTranscryptSite) self.banner.addEventListener ('mousedown', self.gotoTranscryptSite) self.banner.style.fontFamily = 'arial' self.banner.innerHTML = ( '<span id="bannerLarge"><font color="777777">www.<b><i>' + '<font color="ff4422">T<font color="ffb000">r<font color="228822">a<font color="3366ff">n' + '<font color="ff4422">s<font color="ffb000">c<font color="228822">r<font color="3366ff">y<font color="ffb000">p<font color="228822">t' + '</i></b><font color="777777">.org<font size={}><font color="cccccc"></span>' + '<span id="bannerSmall"><i> Write your apps in Python for free!</i></span>' ) self.all.appendChild (self.banner) self.bannerLarge = document.getElementById ('bannerLarge') self.bannerSmall = document.getElementById ('bannerSmall') self.audio = __new__ (Audio ('ios_app.mp3')) window.onresize = self.rightSize self.rightSize () def gotoTranscryptSite (self): document.location.href = 'http://www.transcrypt.org' def roll (self, dice): frameIndex = 10 self.audio.play () def frame (): nonlocal frameIndex frameIndex -= 1 dice.inner.innerHTML = random.randint (1, 6) if frameIndex: dice.style.color = random.choice (('red', 'green', 'blue', 'yellow')) setTimeout (frame, 100) else: dice.style.backgroundColor = dice.normalColor dice.style.color = 'white' frame () def rightSize (self): self.pageWidth = window.innerWidth self.pageHeight = window.innerHeight portrait = self.pageHeight > self.pageWidth for index, dice in enumerate (self.dices): if self.pageHeight > self.pageWidth: # Portrait dice.style.height = 0.3 * self.pageHeight dice.style.width = 0.4 * self.pageWidth dice.style.top = (0.03 + (index if index < 3 else index - 3) * 0.32) * self.pageHeight dice.style.left = (0.06 if index < 3 else 0.54) * self.pageWidth charBoxSide = 0.3 * self.pageHeight dice.inner.style.top = 0.15 * self.pageHeight - 0.6 * charBoxSide dice.inner.style.left = 0.2 * self.pageWidth - 0.5 * charBoxSide self.banner.style.top = 0.975 * self.pageHeight self.banner.style.left = 0.06 * self.pageWidth self.bannerLarge.style.fontSize = 0.017 * self.pageHeight self.bannerSmall.style.fontSize = 0.014 * self.pageHeight else: # Landscape dice.style.height = 0.4 * self.pageHeight dice.style.width = 0.3 * self.pageWidth dice.style.top = (0.06 if index < 3 else 0.54) * self.pageHeight dice.style.left = (0.03 + (index if index < 3 else index - 3) * 0.32) * self.pageWidth charBoxSide = 0.4 * self.pageHeight dice.inner.style.top = 0.2 * self.pageHeight - 0.6 * charBoxSide dice.inner.style.left = 0.15 * self.pageWidth - 0.5 * charBoxSide self.banner.style.top = 0.95 * self.pageHeight self.banner.style.left = 0.03 * self.pageWidth self.bannerLarge.style.fontSize = 0.015 * self.pageWidth self.bannerSmall.style.fontSize = 0.012 * self.pageWidth dice.inner.style.height = charBoxSide dice.inner.style.width = charBoxSide dice.inner.style.fontSize = charBoxSide dice = Dice ()

ios_app.html <html manifest="cache.manifest"> <!-- v45 --> <head> <meta name="apple-mobile-web-app-capable" content="yes"> <meta name="apple-mobile-web-app-status-bar-style" content="black"> <meta name="apple-mobile-web-app-title" content="Dice"> <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no"> <link rel="apple-touch-icon" href="ios_app.png"> </head> <body> <script type="module"> import * as ios_app from "./__target__/ios_app.js"; window.ios_app = ios_app; </script> </body> </html>

cache.manifest CACHE MANIFEST # v45 CACHE: ios_app.html ios_app.mp3 __javascript__/ios_app.js

N.B.1 Cache manifests have to be served with mime type text/cache-manifest.

N.B.2 For native behaviour, e.g. no visible address bar, the app must indeed be added to the home screen of your iOS device.

6.4. Example: D3.js

The D3.js graphics library offers animation by data driven DOM manipulation. It combines well with class based object oriented programming as supported by Transcrypt, leading to applications that are easy to understand and maintain.

d3js_demo.py class Spawn: def __init__ (self, width, height): self.width, self.height, self.spacing = self.fill = width, height, 100, d3.scale.category20 () self.svg = d3.select ('body' ) .append ('svg' ) .attr ('width', self.width ) .attr ('height', self.height ) .on ('mousemove', self.mousemove ) .on ('mousedown', self.mousedown) self.svg.append ('rect' ) .attr ('width', self.width ) .attr ('height', self.height) self.cursor = self.svg.append ('circle' ) .attr ('r', self.spacing ) .attr ('transform', 'translate ({}, {})' .format (self.width / 2, self.height / 2) ) .attr ('class', 'cursor') self.force = d3.layout.force ( ) .size ([self.width, self.height] ) .nodes ([{}] ) .linkDistance (self.spacing ) .charge (-1000 ) .on ('tick', self.tick) self.nodes, self.links, self.node, self.link = self.force.nodes (), self.force.links (), self.svg.selectAll ('.node'), self.svg.selectAll ('.link') self.restart () def mousemove (self): self.cursor.attr ('transform', 'translate (' + d3.mouse (self.svg.node ()) + ')') def mousedown (self): def pushLink (target): x, y = target.x - node.x, target.y - node.y if Math.sqrt (x * x + y * y) < self.spacing: spawn.links.push ({'source': node, 'target': target}) point = d3.mouse (self.svg.node ()) node = {'x': point [0], 'y': point [1]} self.nodes.push (node) self.nodes.forEach (pushLink) self.restart () def tick (self): self.link.attr ('x1', lambda d: d.source.x ) .attr ('y1', lambda d: d.source.y ) .attr ('x2', lambda d: d.target.x ) .attr ('y2', lambda d: d.target.y) self.node.attr ('cx', lambda d: d.x ) .attr ('cy', lambda d: d.y) def restart (self): self.link = self.link.data (self.links) self.link.enter ( ) .insert ('line', '.node' ) .attr('class', 'link') self.node = self.node.data (self.nodes) self.node.enter ( ) .insert ('circle', '.cursor' ) .attr ('class', 'node' ) .attr ('r', 7 ) .call (self.force.drag) self.force.start () spawn = Spawn (window.innerWidth, window.innerHeight)

d3js_demo.js // Transcrypt'ed from Python, 2023-04-22 17:11:03 import {AssertionError, AttributeError, BaseException, DeprecationWarning, Exception, IndexError, IterableError, KeyError, NotImplementedError, RuntimeWarning, StopIteration, UserWarning, ValueError, Warning, __JsIterator__, __PyIterator__, __Terminal__, __add__, __and__, __call__, __class__, __envir__, __eq__, __floordiv__, __ge__, __get__, __getcm__, __getitem__, __getslice__, __getsm__, __gt__, __i__, __iadd__, __iand__, __idiv__, __ijsmod__, __ilshift__, __imatmul__, __imod__, __imul__, __in__, __init__, __ior__, __ipow__, __irshift__, __isub__, __ixor__, __jsUsePyNext__, __jsmod__, __k__, __kwargtrans__, __le__, __lshift__, __lt__, __matmul__, __mergefields__, __mergekwargtrans__, __mod__, __mul__, __ne__, __neg__, __nest__, __or__, __pow__, __pragma__, __pyUseJsNext__, __rshift__, __setitem__, __setproperty__, __setslice__, __sort__, __specialattrib__, __sub__, __super__, __t__, __terminal__, __truediv__, __withblock__, __xor__, abs, all, any, assert, bool, bytearray, bytes, callable, chr, copy, deepcopy, delattr, dict, dir, divmod, enumerate, filter, float, format, getattr, hasattr, input, int, isinstance, issubclass, len, list, map, max, min, object, ord, pow, print, property, py_TypeError, py_iter, py_metatype, py_next, py_reversed, py_typeof, range, repr, round, set, setattr, sorted, str, sum, tuple, zip} from './org.transcrypt.__runtime__.js'; var __name__ = '__main__'; export var Spawn = __class__ ('Spawn', [object], { __module__: __name__, get __init__ () {return __get__ (this, function (self, width, height) { var __left0__ = tuple ([width, height, 100, d3.scale.category20 ()]); self.width = __left0__ [0]; self.height = __left0__ [1]; self.spacing = __left0__ [2]; self.fill = __left0__; self.svg = d3.select ('body').append ('svg').attr ('width', self.width).attr ('height', self.height).on ('mousemove', self.mousemove).on ('mousedown', self.mousedown); self.svg.append ('rect').attr ('width', self.width).attr ('height', self.height); self.cursor = self.svg.append ('circle').attr ('r', self.spacing).attr ('transform', 'translate ({}, {})'.format (self.width / 2, self.height / 2)).attr ('class', 'cursor'); self.force = d3.layout.force ().size ([self.width, self.height]).nodes ([dict ({})]).linkDistance (self.spacing).charge (-(1000)).on ('tick', self.tick); var __left0__ = tuple ([self.force.nodes (), self.force.links (), self.svg.selectAll ('.node'), self.svg.selectAll ('.link')]); self.nodes = __left0__ [0]; self.links = __left0__ [1]; self.node = __left0__ [2]; self.link = __left0__ [3]; self.restart (); });}, get mousemove () {return __get__ (this, function (self) { self.cursor.attr ('transform', ('translate (' + d3.mouse (self.svg.node ())) + ')'); });}, get mousedown () {return __get__ (this, function (self) { var pushLink = function (target) { var __left0__ = tuple ([target.x - node.x, target.y - node.y]); var x = __left0__ [0]; var y = __left0__ [1]; if (Math.sqrt (x * x + y * y) < self.spacing) { spawn.links.push (dict ({'source': node, 'target': target})); } }; var point = d3.mouse (self.svg.node ()); var node = dict ({'x': point [0], 'y': point [1]}); self.nodes.push (node); self.nodes.forEach (pushLink); self.restart (); });}, get tick () {return __get__ (this, function (self) { self.link.attr ('x1', (function __lambda__ (d) { return d.source.x; })).attr ('y1', (function __lambda__ (d) { return d.source.y; })).attr ('x2', (function __lambda__ (d) { return d.target.x; })).attr ('y2', (function __lambda__ (d) { return d.target.y; })); self.node.attr ('cx', (function __lambda__ (d) { return d.x; })).attr ('cy', (function __lambda__ (d) { return d.y; })); });}, get restart () {return __get__ (this, function (self) { self.link = self.link.data (self.links); self.link.enter ().insert ('line', '.node').attr ('class', 'link'); self.node = self.node.data (self.nodes); self.node.enter ().insert ('circle', '.cursor').attr ('class', 'node').attr ('r', 7).call (self.force.drag); self.force.start (); });} }); export var spawn = Spawn (window.innerWidth, window.innerHeight); //# sourceMappingURL=d3js_demo.map

6.5. Example: React

React is a JavaScript library for easy creation of interactive UI’s. Changes to the UI are made by fast manipulation of a light-weight virtual DOM. The real DOM, which is much slower to manipulate, is then compared with the altered virtual DOM and updated efficiently in a minimum number of steps. This way of working leads to good performance, at the same time keeping a straightforward structure of application UI code, since the complexities of optimizing DOM updates are left to the React library. React is unintrusive and mixes well with Transcrypt, allowing creation of extensive web applications that combine maintainability with speed. This example once again clearly illustrates the philosophy behind Transcrypt: rather than confining you to a “parallel” universe that could never keep up, Transcrypt offers you direct access to the ever expanding universe of innovative JavaScript libraries.

react_demo.py from org.reactjs import createElement, useState, useEffect, useRef from org.reactjs.dom import render as react_render # Helper functions def h(elm_type, props='', *args): return createElement(elm_type, props, *args) def render(react_element, destination_id, callback=lambda: None): container = document.getElementById(destination_id) react_render(react_element, container, callback) def useInterval(func, delay=None): # can be used as `useInterval(func, delay)` # or as `@useInterval(delay)` if delay is None: delay = func return lambda fn: useInterval(fn, delay) ref = useRef(func) ref.current = func @useEffect.withDeps(delay) def setup(): id = setInterval(lambda: ref.current(), delay) return lambda: clearInterval(id) return func # Create a component def Hello(props): count, setCount = useState(0) @useInterval(1000) def updateCounter(): setCount(count+1) return h( 'div', {'className': 'maindiv'}, h('h1', None, 'Hello ', props['name']), h('p', None, 'Lorem ipsum dolor sit ame.'), h('p', None, 'Counter: ', count), h( 'button', {'onClick': updateCounter}, 'Increment', ) ) # Render the component in a 'container' div element = React.createElement(Hello, {'name': 'React!'}) render(element, 'container')

react_demo.js // Transcrypt'ed from Python, 2023-04-22 17:11:15 import {AssertionError, AttributeError, BaseException, DeprecationWarning, Exception, IndexError, IterableError, KeyError, NotImplementedError, RuntimeWarning, StopIteration, UserWarning, ValueError, Warning, __JsIterator__, __PyIterator__, __Terminal__, __add__, __and__, __call__, __class__, __envir__, __eq__, __floordiv__, __ge__, __get__, __getcm__, __getitem__, __getslice__, __getsm__, __gt__, __i__, __iadd__, __iand__, __idiv__, __ijsmod__, __ilshift__, __imatmul__, __imod__, __imul__, __in__, __init__, __ior__, __ipow__, __irshift__, __isub__, __ixor__, __jsUsePyNext__, __jsmod__, __k__, __kwargtrans__, __le__, __lshift__, __lt__, __matmul__, __mergefields__, __mergekwargtrans__, __mod__, __mul__, __ne__, __neg__, __nest__, __or__, __pow__, __pragma__, __pyUseJsNext__, __rshift__, __setitem__, __setproperty__, __setslice__, __sort__, __specialattrib__, __sub__, __super__, __t__, __terminal__, __truediv__, __withblock__, __xor__, abs, all, any, assert, bool, bytearray, bytes, callable, chr, copy, deepcopy, delattr, dict, dir, divmod, enumerate, filter, float, format, getattr, hasattr, input, int, isinstance, issubclass, len, list, map, max, min, object, ord, pow, print, property, py_TypeError, py_iter, py_metatype, py_next, py_reversed, py_typeof, range, repr, round, set, setattr, sorted, str, sum, tuple, zip} from './org.transcrypt.__runtime__.js'; import {render as react_render} from './org.reactjs.dom.js'; import {createElement, useEffect, useRef, useState} from './org.reactjs.js'; var __name__ = '__main__'; export var h = function (elm_type, props) { if (typeof props == 'undefined' || (props != null && props.hasOwnProperty ("__kwargtrans__"))) {; var props = ''; }; var args = tuple ([].slice.apply (arguments).slice (2)); return createElement (elm_type, props, ...args); }; export var render = function (react_element, destination_id, callback) { if (typeof callback == 'undefined' || (callback != null && callback.hasOwnProperty ("__kwargtrans__"))) {; var callback = (function __lambda__ () { return null; }); }; var container = document.getElementById (destination_id); react_render (react_element, container, callback); }; export var useInterval = function (func, delay) { if (typeof delay == 'undefined' || (delay != null && delay.hasOwnProperty ("__kwargtrans__"))) {; var delay = null; }; if (delay === null) { var delay = func; return (function __lambda__ (fn) { return useInterval (fn, delay); }); } var ref = useRef (func); ref.current = func; var setup = useEffect.withDeps (delay) (function () { var id = setInterval ((function __lambda__ () { return ref.current (); }), delay); return (function __lambda__ () { return clearInterval (id); }); }); return func; }; export var Hello = function (props) { var __left0__ = useState (0); var count = __left0__ [0]; var setCount = __left0__ [1]; var updateCounter = useInterval (1000) (function () { setCount (count + 1); }); return h ('div', dict ({'className': 'maindiv'}), h ('h1', null, 'Hello ', props ['name']), h ('p', null, 'Lorem ipsum dolor sit ame.'), h ('p', null, 'Counter: ', count), h ('button', dict ({'onClick': updateCounter}), 'Increment')); }; export var element = React.createElement (Hello, dict ({'name': 'React!'})); render (element, 'container'); //# sourceMappingURL=react_demo.map

6.6. Example: Riot

Riot is a UI framework that combines the use of custom tags and a virtual DOM, much like the one in React. Custom tags look like ordinary HTML tags, but whereas HTML tags only define structure, Riot tags define structure, style and behaviour. Custom tags are compiled to JavaScript by a compiler that comes with Riot. With these custom tags as reusable components, web pages can be built. Riot itself is tiny, and the virtual DOM allows for fast adaptation of page content.

riot_demo.html <!DOCTYPE html> <html> <head> <meta charset="UTF-8" /> <title>Hello PyRiot ;-)</title> <!-- for transcrypted version we do not need the compiler. for the classic version you can use riot+compiler --> <script src="https://cdn.jsdelivr.net/riot/2.5/riot.js"></script> <style> body {font-family:arial;font-size:30px;padding:50px;} h1 {font-size:50px;color:#0000ff;} </style> </head> <body> <!-- classic riot (compiled on server, could be done in browser) --> <sample id="s1"></sample> <script src="tags/sample.js"></script> <script>riot.mount('sample')</script> <!-- transcrypted version (transpiled on server, using python) --> <sample2 id='s2' label="nr1"></sample2> <mp2 id='s3' label="nr2"></mp2> <!-- the transpiled tag's js --> <script type="module"> import * as riot_demo from "./__target__/riot_demo.js" // register var cls = riot_demo.Sample2 riot.tag2('sample2', cls.template, cls.style, '', function(opts) { new cls(this, opts)}) document.t1 = riot.mount('sample2')[0].update() document.t2 = riot.mount('#s3', 'sample2')[0] document.t2.update() </script> </body> </html>

sample.tag, a classic Riot tag // vim: ft=html <sample> <h1>Riot Native Tag</h1> <h5 each="{lv}">name: {name} - counter: {this.count()}</h5> <script> this.counter = 0 // riot's synctactic sugar: count() { this.counter += 1; return this.counter } // to test stuff on console: window.native_tag = this this.on('update', function() { this.lv = [{name: 'n1'}, {'name': 'n2'}] this.update() }) </script> <style scoped> h1 {color: red} </style> </sample>

sample.js, compiled by Riot // vim: ft=html riot.tag2('sample', '<h1>Riot Native Tag</h1> <h5 each="{lv}">name: {name} - counter: {this.count()}</h5>', 'sample h1,[riot-tag="sample"] h1,[data-is="sample"] h1{color: red}', '', function(opts) { this.counter = 0 this.count = function() { this.counter += 1; return this.counter }.bind(this) window.native_tag = this this.on('update', function() { this.lv = [{name: 'n1'}, {'name': 'n2'}] this.update() }) });

riot_tag.py, baseclass of all Transcrypt Riot tags # Parent Class for a Transcrypt Riot Tag # # This binds the namespace of a riot tag at before-mount event 100% to that of # the a transcrypt instance, except members which begin with an underscore, those # are private to the transcrypt object. # # The 4 riot lifecycle events are bound to overwritable python functions. # # Immutables (strings, ints, ...) are bound to property functions within the tag, # so the templates work, based on state in the transcrypt tag. # State can be changed in the riot tag as well but take care to not create new # references - you won't find them in the Transcrypt tag. # # # Best Practices: # - mutate state only in the transcrypt tag. # - declare all variables so they are bound into the riot tag # - IF you declare new variables to be used in templates, run # self.bind_vars(self.riot_tag) # TODO: docstring format not accepted by the transpiler, strange. __author__ = "Gunther Klessinger, gk@axiros.com, Germany" # just a minihack to get some colors, mainly to test lamdas and imports: from color import colors, cprint as col_print c = colors M, I, L, R, B = c['purple'], c['orange'], c['gray'], c['red'], c['black'] lifecycle_ev = ['before-mount', 'mount', 'update', 'unmount'] cur_tag_col = 0 class RiotTag: """ taking care for extending the riot tag obj with functions and immutable(!) properties of derivations of us See counter. """ debug = None # placeholders: template = '<h1>it worx</h1>' style = '' node_name = 'unmounted' opts = None def __init__(self, tag, opts): # opts into the python instance, why not: self.opts = opts self._setup_tag(tag) # giving ourselves a unique color: global cur_tag_col # working (!) cur_tag_col = (cur_tag_col + 1) % len(colors) # TODO values() on a dict self.my_col = colors.items()[cur_tag_col][1] def _setup_tag(self, tag): # keeping mutual refs tag.py_obj = self self.riot_tag = tag # making the event system call self's methods: handlers = {} for ev in lifecycle_ev: f = getattr(self, ev.replace('-', '_')) if f: # this.on('mount', function() {...}): # whats nicer? tag.on(ev, f) def pp(self, *msg): # color flash in the console. one color per tag instance. col_print( #B(self.riot_tag._riot_id), L('<', self.my_col(self.node_name, self.my_col), '/> '), M(' '.join([s for s in msg]))) def _lifecycle_ev(self, mode): if self.debug: self.pp(mode + 'ing') # overwrite these for your specific one: def update (self): self._lifecycle_ev('update') def mount (self): self._lifecycle_ev('mount') def unmount(self): self._lifecycle_ev('unmount') def before_mount(self): self._lifecycle_ev('before-mount') return self.bind_vars() def bind_vars(self): tag = self.riot_tag self.node_name = tag.root.nodeName.lower() self.debug and self.pp('binding vars') # binding self's functions into the tag instance # binding writable properties to everything else (e.g. ints, strs...) tag._immutables = im = [] lc = lifecycle_ev for k in dir(self): # private or lifecycle function? don't bind: if k[0] == '_' or k in lifecycle_ev or k == 'before_mount': continue v = getattr(self, k) # these I can't write in python. Lets use JS then. # TODO there should be, maybe some mocking facility for code # testing w/o a js runtime: __pragma__('js', '{}', ''' typeof v === "function" || typeof v === "object" ? tag[k] = self[k] : tag._immutables.push(k)''') __pragma__('js', '{}', ''' var i = tag._immutables, py = self i.forEach(function(k, j, i) { Object.defineProperty(tag, k, { get: function() { return self[k]}, set: function(v) { self[k] = v } }) })''')

riot_tag.js, compiled by Transcrypt // Transcrypt'ed from Python, 2023-04-22 17:11:21 import {AssertionError, AttributeError, BaseException, DeprecationWarning, Exception, IndexError, IterableError, KeyError, NotImplementedError, RuntimeWarning, StopIteration, UserWarning, ValueError, Warning, __JsIterator__, __PyIterator__, __Terminal__, __add__, __and__, __call__, __class__, __envir__, __eq__, __floordiv__, __ge__, __get__, __getcm__, __getitem__, __getslice__, __getsm__, __gt__, __i__, __iadd__, __iand__, __idiv__, __ijsmod__, __ilshift__, __imatmul__, __imod__, __imul__, __in__, __init__, __ior__, __ipow__, __irshift__, __isub__, __ixor__, __jsUsePyNext__, __jsmod__, __k__, __kwargtrans__, __le__, __lshift__, __lt__, __matmul__, __mergefields__, __mergekwargtrans__, __mod__, __mul__, __ne__, __neg__, __nest__, __or__, __pow__, __pragma__, __pyUseJsNext__, __rshift__, __setitem__, __setproperty__, __setslice__, __sort__, __specialattrib__, __sub__, __super__, __t__, __terminal__, __truediv__, __withblock__, __xor__, abs, all, any, assert, bool, bytearray, bytes, callable, chr, copy, deepcopy, delattr, dict, dir, divmod, enumerate, filter, float, format, getattr, hasattr, input, int, isinstance, issubclass, len, list, map, max, min, object, ord, pow, print, property, py_TypeError, py_iter, py_metatype, py_next, py_reversed, py_typeof, range, repr, round, set, setattr, sorted, str, sum, tuple, zip} from './org.transcrypt.__runtime__.js'; import {cprint as col_print, colors} from './color.js'; var __name__ = 'riot_tag'; export var __author__ = 'Gunther Klessinger, gk@axiros.com, Germany'; export var c = colors; var __left0__ = tuple ([c ['purple'], c ['orange'], c ['gray'], c ['red'], c ['black']]); export var M = __left0__ [0]; export var I = __left0__ [1]; export var L = __left0__ [2]; export var R = __left0__ [3]; export var B = __left0__ [4]; export var lifecycle_ev = ['before-mount', 'mount', 'update', 'unmount']; export var cur_tag_col = 0; export var RiotTag = __class__ ('RiotTag', [object], { __module__: __name__, debug: null, template: '<h1>it worx</h1>', style: '', node_name: 'unmounted', opts: null, get __init__ () {return __get__ (this, function (self, tag, opts) { self.opts = opts; self._setup_tag (tag); cur_tag_col = __mod__ (cur_tag_col + 1, len (colors)); self.my_col = colors.py_items () [cur_tag_col] [1]; });}, get _setup_tag () {return __get__ (this, function (self, tag) { tag.py_obj = self; self.riot_tag = tag; var handlers = dict ({}); for (var ev of lifecycle_ev) { var f = getattr (self, ev.py_replace ('-', '_')); if (f) { tag.on (ev, f); } } });}, get pp () {return __get__ (this, function (self) { var msg = tuple ([].slice.apply (arguments).slice (1)); col_print (L ('<', self.my_col (self.node_name, self.my_col), '/> '), M (' '.join ((function () { var __accu0__ = []; for (var s of msg) { __accu0__.append (s); } return __accu0__; }) ()))); });}, get _lifecycle_ev () {return __get__ (this, function (self, mode) { if (self.debug) { self.pp (mode + 'ing'); } });}, get py_update () {return __get__ (this, function (self) { self._lifecycle_ev ('update'); });}, get mount () {return __get__ (this, function (self) { self._lifecycle_ev ('mount'); });}, get unmount () {return __get__ (this, function (self) { self._lifecycle_ev ('unmount'); });}, get before_mount () {return __get__ (this, function (self) { self._lifecycle_ev ('before-mount'); return self.bind_vars (); });}, get bind_vars () {return __get__ (this, function (self) { var tag = self.riot_tag; self.node_name = tag.root.nodeName.lower (); self.debug && self.pp ('binding vars'); var __left0__ = []; tag._immutables = __left0__; var im = __left0__; var lc = lifecycle_ev; for (var k of dir (self)) { if (k [0] == '_' || __in__ (k, lifecycle_ev) || k == 'before_mount') { continue; } var v = getattr (self, k); typeof v === "function" || typeof v === "object" ? tag[k] = self[k] : tag._immutables.push(k) } var i = tag._immutables, py = self i.forEach(function(k, j, i) { Object.defineProperty(tag, k, { get: function() { return self[k]}, set: function(v) { self[k] = v } }) }) });} }); //# sourceMappingURL=riot_tag.map

riot_demo.py, a derived Transcrypt Riot tag class # an example user tag, using RiotTag from riot_tag import RiotTag class P(RiotTag): debug = 1 # never do mutables on class level. this is just to check if transpiler # creates the same behaviour - and it does, a second tag instance gets # the same lv object: lv = [{'name': 'n0'}] # immuatble on class level. does a second instance start at 1? # answer: yes, perfect: counter = 1 template = ''' <div><h1>Riot Transcrypt Tag Instance {label}</h1> <div>INNER</div></div> ''' def count_up(self): self.counter = self.counter + 1 self.pp('counter:', self.counter, 'len lv:', len(self.lv), 'adding one lv' ) self.lv.append({'name': 'n' + self.counter}) return self.counter # try some inheritance... class Sample2(P): # ... and change the state at every update, just for fun: template = P.template.replace('INNER', ''' <div> <h5 each="{lv}">name: {name} - counter: {count_up()}</h5> </div> ''') # no scoped styles currently style = '''sample2 h5 {color: green}''' def __init__(self, tag, opts): self.label = opts.label.capitalize() # this rocks so much. # alternative to super: RiotTag.__init__(self, tag, opts) # uncomment next line and chrome will stop: # debugger self.pp('tag init', 'adding 2 lv') # mutating the lv object: self.lv.extend([{'name': 'n1'}, {'name': 'n2'}]) def update(self): self.pp('update handler in the custom tag, calling super') RiotTag.update(self)

riot_demo.js, compiled by Transcrypt // Transcrypt'ed from Python, 2023-04-22 17:11:21 import {AssertionError, AttributeError, BaseException, DeprecationWarning, Exception, IndexError, IterableError, KeyError, NotImplementedError, RuntimeWarning, StopIteration, UserWarning, ValueError, Warning, __JsIterator__, __PyIterator__, __Terminal__, __add__, __and__, __call__, __class__, __envir__, __eq__, __floordiv__, __ge__, __get__, __getcm__, __getitem__, __getslice__, __getsm__, __gt__, __i__, __iadd__, __iand__, __idiv__, __ijsmod__, __ilshift__, __imatmul__, __imod__, __imul__, __in__, __init__, __ior__, __ipow__, __irshift__, __isub__, __ixor__, __jsUsePyNext__, __jsmod__, __k__, __kwargtrans__, __le__, __lshift__, __lt__, __matmul__, __mergefields__, __mergekwargtrans__, __mod__, __mul__, __ne__, __neg__, __nest__, __or__, __pow__, __pragma__, __pyUseJsNext__, __rshift__, __setitem__, __setproperty__, __setslice__, __sort__, __specialattrib__, __sub__, __super__, __t__, __terminal__, __truediv__, __withblock__, __xor__, abs, all, any, assert, bool, bytearray, bytes, callable, chr, copy, deepcopy, delattr, dict, dir, divmod, enumerate, filter, float, format, getattr, hasattr, input, int, isinstance, issubclass, len, list, map, max, min, object, ord, pow, print, property, py_TypeError, py_iter, py_metatype, py_next, py_reversed, py_typeof, range, repr, round, set, setattr, sorted, str, sum, tuple, zip} from './org.transcrypt.__runtime__.js'; import {RiotTag} from './riot_tag.js'; var __name__ = '__main__'; export var P = __class__ ('P', [RiotTag], { __module__: __name__, debug: 1, lv: [dict ({'name': 'n0'})], counter: 1, template: ' <div><h1>Riot Transcrypt Tag Instance {label}</h1>\n <div>INNER</div></div> ', get count_up () {return __get__ (this, function (self) { self.counter = self.counter + 1; self.pp ('counter:', self.counter, 'len lv:', len (self.lv), 'adding one lv'); self.lv.append (dict ({'name': 'n' + self.counter})); return self.counter; });} }); export var Sample2 = __class__ ('Sample2', [P], { __module__: __name__, template: P.template.py_replace ('INNER', '\n <div>\n <h5 each="{lv}">name: {name} - counter: {count_up()}</h5>\n </div>\n '), style: 'sample2 h5 {color: green}', get __init__ () {return __get__ (this, function (self, tag, opts) { self.label = opts.label.capitalize (); RiotTag.__init__ (self, tag, opts); self.pp ('tag init', 'adding 2 lv'); self.lv.extend ([dict ({'name': 'n1'}), dict ({'name': 'n2'})]); });}, get py_update () {return __get__ (this, function (self) { self.pp ('update handler in the custom tag, calling super'); RiotTag.py_update (self); });} }); //# sourceMappingURL=riot_demo.map

6.7. Example: Using input and print in a DOM __terminal__ element in your browser

Without special measures, Transcrypt’s print function prints to the debugging console. However if there’s an element with id __terminal__ in your DOM tree, the print function prints to this element. Moreover, the input function also prints its prompt message to the terminal element. Input is collected using a dialog box and echoed to the terminal element.

This means that you can write applications with blocking I/O, rather than event driven behaviour, e.g. for simple activities or, since they are intuitively easy to comprehend, for educational purposes.

terminal_demo.html <html> <head> <script type="module">import * as terminal_demo from "./__target__/terminal_demo.js";</script> </head> <body> <b> Leave input field blank to quit<br> Refresh browser window to restart<br> </b> <div id='__terminal__'></div> </body> </html>

terminal_demo.py while True: name = input ('What''s your name? ') if name == '': break; print ('Hi', name, 'I am your computer.') age = float (input ('How old are you? ')) if age < 18: print ('Sorry', name, ',', age, 'is too young to drive a car in the Netherlands.') else: print ('OK', name, ',', age, 'is old enough to drive a car in the Netherlands.') print ()

6.8. Example: Using the Parcel.js bundler to package a set of modules written in diverse programming languages

Bundlers are increasingly popular in the world of web development. With the Parcel bundler, it is possible to integrate Transcrypt modules with modules written in other languages. Whenever the source code of any module changes, automatic recompilation and repackaging takes place. Sourcemaps are generated for all non-JavaScript modules, enabling source level debugging in the browser.

In the example, the top level file of the module hierarchy is the html file below:

index.html <html> <head> <meta charset="UTF-8"> <title>parcel-plugin-python</title> </head> <body> <h1>Python+Transcrypt Plugin for Parcel Bundler</h1> <p>[ open the console for program output ]</p> <script src="./index.js"></script> </body> </html>

The html file above refers to the JavaScript file below:

index.js import { main } from "./main.py"; main();

This top level JavaScript file in turn refers to a Python file, that makes use of many modules, some written in Python, some in JavaScript:

main.py from testcontext import Test def main(): '''Main function of the program (called from index.js)''' # sibling module with Test('import sibling') as test: import sibling test.result = sibling.sibling_func(test.random_num) with Test('import sibling as alias_sibling') as test: import sibling as alias_sibling test.result = alias_sibling.sibling_func(test.random_num) with Test('from sibling import sibling_func') as test: from sibling import sibling_func test.result = sibling_func(test.random_num) with Test('from sibling import sibling_func as alias_sibling_func') as test: from sibling import sibling_func as alias_sibling_func test.result = alias_sibling_func(test.random_num) # sibling2 module (using sibling2 because `import * from sibling` would overrride sibling_func above) with Test('from sibling2 import *') as test: from sibling2 import * test.result = sibling2_func(test.random_num) # siblingjs.js (Javascript file import) with Test('import siblingjs') as test: import siblingjs test.result = siblingjs.siblingjs_func(test.random_num) with Test('import siblingjs as alias_siblingjs') as test: import siblingjs as alias_siblingjs test.result = alias_siblingjs.siblingjs_func(test.random_num) with Test('from siblingjs import siblingjs_func') as test: from siblingjs import siblingjs_func test.result = siblingjs_func(test.random_num) with Test('from siblingjs import siblingjs_func as alias_siblingjs_func') as test: from siblingjs import siblingjs_func as alias_siblingjs_func test.result = alias_siblingjs_func(test.random_num) # mymod package (__init__.py file) with Test('import mymod') as test: import mymod test.result = mymod.mymod_func(test.random_num) with Test('import mymod as alias_mymod') as test: import mymod as alias_mymod test.result = alias_mymod.mymod_func(test.random_num) with Test('from mymod import mymod_func') as test: from mymod import mymod_func test.result = mymod_func(test.random_num) with Test('from mymod import mymod_func as alias_mymod_func') as test: from mymod import mymod_func as alias_mymod_func test.result = alias_mymod_func(test.random_num) # mymod.child (subdir module) with Test('import mymod.child') as test: import mymod.child test.result = mymod.child.child_func(test.random_num) with Test('alias_child.child_func') as test: import mymod.child as alias_child test.result = alias_child.child_func(test.random_num) with Test('from mymod.child import child_func') as test: from mymod.child import child_func test.result = child_func(test.random_num) with Test('from mymod.child import child_func as alias_child_func') as test: from mymod.child import child_func as alias_child_func test.result = alias_child_func(test.random_num) with Test('import mymod.grandchildmod') as test: import mymod.grandchildmod test.result = mymod.grandchildmod.grandchildmod_func(test.random_num) with Test('import mymod.grandchildmod as alias_grandchildmod') as test: import mymod.grandchildmod as alias_grandchildmod test.result = alias_grandchildmod.grandchildmod_func(test.random_num) with Test('from mymod.grandchildmod.grandchild import grandchild_func') as test: from mymod.grandchildmod.grandchild import grandchild_func test.result = grandchild_func(test.random_num) with Test('from mymod.grandchildmod.grandchild import grandchild_func as alias_grandchild_func') as test: from mymod.grandchildmod.grandchild import grandchild_func as alias_grandchild_func test.result = alias_grandchild_func(test.random_num)

Whenever a source file of this mixed bag of modules is changed, the whole module hierarchy is rebuilt and repackaged. The bundler gets its information from the .project file in the __target__ directory. Consequently Transcrypt can be fully integrated in an automated build process for a project featuring an arbitrary mix of source languages. With this feature, Python has truly become a first class citizen in the browser world.