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

[adorilson]

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.

• Issue: Make turtle.pensize smarter #133244

[ZeroIntensity]

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.

[github-actions]

This PR is stale because it has been open for 30 days with no activity.

[StanFromIreland]

What about pen(pensize=-1)?

[adorilson]

Good catch.

I'll address it.

[adorilson]

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.

@StanFromIreland any thought about it?

[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #34205211 | 📁 Comparing 75fec25 against main (f897dbf)

  🔍 Preview build  

498 files changed · + 1 added · ± 459 modified · - 38 deleted

+ Added

• library/asyncio-policy.html

± Modified

• about.html
• bugs.html
• glossary.html
• index.html
• license.html
• py-modindex.html
• c-api/allocation.html
• c-api/apiabiversion.html
• c-api/arg.html
• c-api/buffer.html
• and 449 more...

- Deleted

• improve-page-nojs.html
• improve-page.html
• _static/tachyon-example-flamegraph.html
• _static/tachyon-example-heatmap.html
• c-api/curses.html
• c-api/extension-modules.html
• c-api/interp-lifecycle.html
• c-api/picklebuffer.html
• c-api/profiling.html
• c-api/sentinel.html
• and 28 more...