`TypeError` when trying to deepcopy `argparse.ArgumentParser()`

[kmvanbrunt]

Crash report

What happened?

To reproduce:

import argparse
import copy

parser = argparse.ArgumentParser()
copy.deepcopy(parser)

This results in the following exception.

File ~/.local/share/uv/python/cpython-3.15.0b1-linux-x86_64-gnu/lib/python3.15/copy.py:138, in deepcopy(x, memo)
    136 copier = getattr(x, "__deepcopy__", None)
    137 if copier is not None:
--> 138     y = copier(memo)
    139 else:
    140     reductor = dispatch_table.get(cls)

TypeError: 'str' object is not callable

The root cause is _ColorlessTheme.__getattr__() in argparse.py.

class _ColorlessTheme:
    # A 'fake' theme for no colors
    def __getattr__(self, name):
        # _colorize's no_color themes are just all empty strings
        # by directly using empty strings the import is avoided
        return ""

It returns "" for the __deepcopy__ atrribute, which copy.deepcopy() then tries to call.

CPython versions tested on:

3.15, CPython main branch

Operating systems tested on:

Linux

Output from running 'python -VV' on the command line:

Python 3.15.0b1 (main, May 8 2026, 18:33:09) [Clang 22.1.3 ]

Linked PRs

• gh-149614 - Restore deepcopiability of argparse.ArgumentParser instances #149617

[tleonhardt]

I am also experiencing this bug when using Python 3.15.0b1 and can confirm it happens on Windows, Mac, and Linux. I can also confirm this bug does not exist in earlier versions including 3.15.0a8 and 3.14.5rc1

[StanFromIreland]

Introduced in 8cad740. CC @DavidCEllis

[DavidCEllis]

Yes, it probably shouldn't return empty strings for magic methods...

Also we'll need to add a test for copiability.