`tkinter.filedialog.askopenfilename` raises TypeError when `filetypes=None`

[windymilla]

Bug report

Bug description:

tkinter.filedialog.askopenfilename raises TypeError when filetypes=None, despite docs stating that None is acceptable.

Expected behavior:

Passing filetypes=None should behave the same as omitting the option and open the file dialog without restricting file types.

Actual behavior:

A TypeError: 'NoneType' object is not iterable exception is raised before the dialog is shown.

Root cause:

In Lib/tkinter/filedialog.py:

self.options["filetypes"] = tuple(self.options["filetypes"])

with no guard for None

Minimal example:

from tkinter import Tk, filedialog

root = Tk()
root.withdraw()

filedialog.askopenfilename(filetypes=None)

Python Versions: 3.14.0rc3 and 3.14.2

OS: Windows 11

CPython versions tested on:

3.14

Operating systems tested on:

Windows

[ronaldoussoren]

The documentation mentions the following just before the documentation for tkinter.filedialog.askopenfilename:

The following classes and functions provide file dialog windows that combine a native look-and-feel with configuration options to customize behaviour. The following keyword arguments are applicable to the classes and functions listed below:
...
filetypes - a sequence of (label, pattern) tuples, ‘*’ wildcard is allowed

This does not mention that None is a valid value for this option.

Where is documented that None is a valid value?

[windymilla]

Thanks @ronaldoussoren

Following up with some additional context on the documentation question you raised.

While CPython itself has no explicit annotations here, the canonical typing in typeshed does allow None for filetypes. In typeshed/stdlib/tkinter/filedialog.pyi, askopenfilename is annotated as:

filetypes: Sequence[tuple[str, str]] | None

Other parameters also accept None

This means passing None is considered type-correct by static type checkers (mypy, pyright, pylance), but currently fails at runtime with an internal TypeError.

I wanted to add this for completeness, as it may be relevant to whether the runtime behaviour or the typing should be adjusted.