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gh-133244: TPen.pensize raises TurtleGraphicsError if called with a negative number #135268

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gh-133244: TPen.pensize raises TurtleGraphicsError if called with a negative number #135268

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@adorilson adorilson commented Jun 8, 2025 •
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Fix #133244.

Before

>>> import turtle
>>> turtle.pensize(-1)
>>> turtle.forward(100)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<string>", line 8, in forward
  File "/home/adorilson/anaconda3/lib/python3.12/turtle.py", line 1636, in forward
    self._go(distance)
  File "/home/adorilson/anaconda3/lib/python3.12/turtle.py", line 1597, in _go
    self._goto(ende)
  File "/home/adorilson/anaconda3/lib/python3.12/turtle.py", line 3248, in _goto
    screen._drawline(self.drawingLineItem,
  File "/home/adorilson/anaconda3/lib/python3.12/turtle.py", line 543, in _drawline
    self.cv.itemconfigure(lineitem, width=width)
  File "<string>", line 1, in itemconfigure
  File "/home/adorilson/anaconda3/lib/python3.12/tkinter/__init__.py", line 2988, in itemconfigure
    return self._configure(('itemconfigure', tagOrId), cnf, kw)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/adorilson/anaconda3/lib/python3.12/tkinter/__init__.py", line 1712, in _configure
    self.tk.call(_flatten((self._w, cmd)) + self._options(cnf))
_tkinter.TclError: bad screen distance "-1"

Now

>>> import turtle
>>> turtle.pensize(-1)
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    turtle.pensize(-1)
    ~~~~~~~~~~~~~~^^^^
  File "<string>", line 8, in pensize
  File "/home/adorilson/workspace/cpython/Lib/turtle.py", line 2145, in pensize
    raise TurtleGraphicsError(f"width argument must be a positive number. It was {width}.")
turtle.TurtleGraphicsError: width argument must be a positive number. It was -1.

For now, the 0 behaviour wasn't changed, but I think it would.

If we call turtle.pensize(0) it changes the width to 0, but when the turtle draws, the real line's width is 1. It seems to be a misconception. However, change could be a backwards compatibility concern. Perhaps we can schedule a change for now with a DeprecationWarning.

vstinner and others added 5 commits June 7, 2025 12:29
@vstinner @adorilson
pythongh-106320: Remove private _PyInterpreterState functions (python…
6521268 
…#106335)

Remove private _PyThreadState and _PyInterpreterState C API
functions: move them to the internal C API (pycore_pystate.h and
pycore_interp.h). Don't export most of these functions anymore, but
still export functions used by tests.

Remove _PyThreadState_Prealloc() and _PyThreadState_Init() from the C
API, but keep it in the stable API.
@adorilson
Doc: minor change
7890388
@adorilson
Revert "Doc: minor change"
50763c4 
This reverts commit ebfa093.
@adorilson
pythongh-133244: Add TPen.pensize tests
558d97f
@adorilson
pythongh-133244 TPen.pensize raises TurtleGraphicsError if called wit…
08c5c48 
…h a negative number
@bedevere-app bedevere-app bot mentioned this pull request Jun 8, 2025
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ZeroIntensity
ZeroIntensity reviewed Jun 9, 2025
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This is user-facing, so please add a news entry. The easiest way will be with blurb-it, unless you already have blurb installed locally.

Lib/turtle.py Outdated
@@ -2141,7 +2141,10 @@ def pensize(self, width=None):
"""
if width is None:
return self._pensize
self.pen(pensize=width)
elif width < 0:
raise TurtleGraphicsError(f"width argument must be a positive number. It was {width}.")
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I'm not aware of the phrasing "it was [x]" in any other error messages. How about something like width must be a positive number, but got {width}?

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@adorilson adorilson Jun 9, 2025 •
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Done it and blurb, as well.

@ZeroIntensity ZeroIntensity added needs backport to 3.13 bugs and security fixes needs backport to 3.14 bugs and security fixes labels Jun 9, 2025
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Make turtle.pensize smarter
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