Setting None to skip_file_prefixes of warnings.warn() gets error

[hyperkai]

Bug report

Bug description:

The doc of warnings.warn() says skip_file_prefixes is None by default as shown below:

warnings.warn(message, category=None, stacklevel=1, source=None, *, skip_file_prefixes=None)

But, setting None to skip_file_prefixes gets the error as shown below:

import warnings

warnings.warn(message='Warning',
              category=None,
              stacklevel=1,
              source=None,
              skip_file_prefixes=None) # Error
            # ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑ ↑

TypeError: warn() argument 'skip_file_prefixes' must be tuple, not None

CPython versions tested on:

3.13

Operating systems tested on:

Windows

Linked PRs

• gh-125818: Fix incorrect signature of argument skip_file_prefixes in warnings docs #125823
• [3.13] gh-125818: Fix incorrect signature of argument skip_file_prefixes in warnings docs (GH-125823) #126216
• [3.12] gh-125818: Fix incorrect signature of argument skip_file_prefixes in warnings docs (GH-125823) #126217

[tomasr8]

This is probably just a typo in the docs. The default value for that parameter as actually an empty tuple:

cpython/Lib/warnings.py

Lines 302 to 316 in 4848b0b

	def warn(message, category=None, stacklevel=1, source=None,
	*, skip_file_prefixes=()):
	"""Issue a warning, or maybe ignore it or raise an exception."""
	# Check if message is already a Warning object
	if isinstance(message, Warning):
	category = message.__class__
	# Check category argument
	if category is None:
	category = UserWarning
	if not (isinstance(category, type) and issubclass(category, Warning)):
	raise TypeError("category must be a Warning subclass, "
	"not '{:s}'".format(type(category).__name__))
	if not isinstance(skip_file_prefixes, tuple):
	# The C version demands a tuple for implementation performance.
	raise TypeError('skip_file_prefixes must be a tuple of strs.')

(It's also the case for the C module) The docs mention it too:

[...] If supplied, it must be a tuple of strings.

Would you like to open a PR to fix the method signature in the docs?

[rruuaanng]

Maybe the task of repairing this document can be entrusted to me.
If there is no comment, I will launch a PR.

[erlend-aasland]

Thanks for the report, Kai, and thanks for the PR, James.