Python turtle gotchas

py-turtle-gotchas.md

Python turtle gotchas

• Summary of gotchas and analysis
• Just installing it is hard:
  • Why does tkinter (or turtle) seem to be missing or broken? Shouldn't it be part of the standard library?
  • Failing to run Turtle Graphics program on MacOS
• turtle.mainloop, turtle.exitonclick or turtle.done in the wrong spot (or forgetting to use them at all, or thinking exitonclick is a normal click handler).
  • Turtle only completes one iteration of a loop and stops at done()
  • Turtle keybinds, why do they keep crashing?
  • Draw a square in Python Turtle
• Too many aliases for every function call, breaking the Zen of Python and introducing confusion.
  • For example, onkey is an alias of onkeyrelease rather than onkeypress.
  • Python turtle.done() alternatives - how do they differ?
• Poorly-named legacy Logo methods like pu and seth (although useful for those with limited typing skills). Does turtle.down() move the turtle downward or put the pen down?
• Weird function names like tracer.
• done() doesn't exit turtle, it actually starts the main (infinite) loop, leading to confusion.
• Confusion between procedural and OOP APIs.
  • What is wrong with my turtle code? Cannot understand
  • Turtle gives error: AttributeError: 'Turtle' object has no attribute 'onkeyrelease'
• "Ghost" turtles:
  • Third clone of the turtle
  • Why is there a second Turtle?
  • Why is there a little arrow in the middle of the screen?
  • Little black square in center of screen after each restart in turtle graphics pong game
  • I'm not able to remove the arrow in python turtle while trying draw a circle of flowers
• Gotchas subclassing turtle:
  • Paddles on my Pong game do not move after pressing the keys on Python 3.11 Turtle Graphics
  • How can I solve the key error in this POO turtle game? (also typoing __init__ as __int__)
  • Ping Pong Game Class Inheritance confusion
  • AttributeError: 'Paddle' object has no attribute 'screen'. Did you mean: '_screen'? and Turtle Subclass "object has no attribute '_shown'" (forgot to call the super class init)
• Forgetting to call Screen().listen() to enable key handlers.
• Calling key handlers immediately:
  • onkeypress() function in turtle module problem
  • paddles wont move in pong game and there's no visible error codes being thrown, am i missing something?
• No clear path to writing a decent real-time rendering loop or handling multiple keypresses easily ("roll it yourself" basically).
  • Hard to move two turtles simultaneously
• tracer(0)/turtle.update() confusion.
  • Turtle doing nothing in embedded Tkinter window
• Turtle images don't rotate
• Hard to keep things in bounds of the screen/window.
• Using while True: turtle.update() to run an event loop rather than ontimer.
  • Snake game in Python using Turtle graphics
  • Python screen crashes after I use screen.tracer(0)
  • Turtles don't appear when using the tracer method
• Writing unreachable code after infinite while loops. and this and this
• Registering one-time key listeners repeatedly in a loop
• Very hard to do many simple things like getting the mouse position.
• Can only load gifs as sprites.
• Naming the file turtle.py: 1, 2.
• Terminating the Tkinter window usually throws a scary-looking, confusing error that isn't related to anything the user did wrong.
• Errors related to Tkinter are almost always confusing.
• No real turtle deallocation mechanism, so you're pretty much forced to write an object pool for apps with lots of turtles (particle systems, etc).
• Confusion using print or input().
• Collecting text input removes key listeners.
• Errors changing colors.
• Typoing key names (lowercase/uppercase), or generally being confused by the list of Tkinter keys.
• Overwriting the turtle module with a variable called turtle.
• Making a clickable button with text (and hovering) is difficult.
• IDEs/linters can't figure out turtle types properly:
  • PyCharm false syntax error using turtle
  • Turtle Library Python: What am I doing when I do screen = Screen() if Screen isn't a class? (two issues, one being the IDE failing to identify a valid method on an object and the other being the Screen() being a function in spite of the uppercased name)
• Calling functions immediately that should be passed to ontimer or listeners
• Accurate timing for animations
• undefined fill behavior
• No good way to relaunch a screen after closing it
• Forgetting to call methods and 'str' object has no attribute 'turtle' in Python turtle
• Assigning to methods rather than calling them
• Turtles are weirdly off center for no reason (TODO: verify and investigate)
• Bugs binding keypresses without a closure: Dynamically passing Turtles to onkeypress() binds always only one of them
• Differences in the turtle API between Python 2 and Python 3:
  • AttributeError: '_Screen' object has no attribute 'mainloop'
  • How can i fix AttributeError: '_Screen' object has no attribute 'onkeypress' in python turtle?
  • Turtle gives error: AttributeError: 'Turtle' object has no attribute 'onkeyrelease'
  • tracer changed from py 2 to 3
• Forgetting to provide a number argument to ontimer.
  • How to manage event-handler recursion in python turtle? (unable to reproduce on a modern machine but worth looking into)
• Calling clearscreen() removes exitonclick() handler: Why isn't exitonclick working in my Python Turtle graphics program?
• Calling .clear() in the wrong place
• There are other similar libraries like Google colab turtle, replit, and trinket that are incompatible with the CPython turtle.
  • For example, they have different arguments
• onkeyrelease fires even if you haven't released the key, if the OS retrigger kicks in.
• Changing the turtle's shape removes click handlers
• Screen size is slightly off on different systems
• Turtle can fail out of the box with a confusing error on Mac: DEPRECATION WARNING: The system version of Tk is deprecated, M1 Mac in Vs Code - global Python
• Forgetting to add parentheses to a function call--not specific to turtle, but definitely a Python gotcha that hits beginners.
• Possible: did colormode change from turtle to screen? check here and add to list if so

TODO: make a library that fixes these issues and offers a real rendering loop (with delta time). Or maybe suggest people use JS or Lua/Love or Pygame.