(Updated from main to fix the Android failure: #142289)

This PR broke instantiating the formatter outside the parser because _theme is no longer set in __init__ as _set_color is no longer called.

import argparse

formatter = argparse.HelpFormatter(prog="program")
formatter.add_usage(usage=None, actions=[], groups=[])
print(formatter.format_help())

This now raises an AttributeError:

Traceback (most recent call last):
  File "/tmp/t.py", line 5, in <module>
    print(formatter.format_help())
          ~~~~~~~~~~~~~~~~~~~~~^^
  File "/tmp/argparse.py", line 303, in format_help
    help = self._root_section.format_help()
  File "/tmp/argparse.py", line 228, in format_help
    item_help = join([func(*args) for func, args in self.items])
                      ~~~~^^^^^^^
  File "/tmp/argparse.py", line 315, in _format_usage
    t = self._theme
        ^^^^^^^^^^^
AttributeError: 'HelpFormatter' object has no attribute '_theme'

This only broke a test over at https://github.com/hamdanal/rich-argparse and I am not sure if it a supported usage of the formatter. Let me know if I need to create an issue/PR.

Hey @hamdanal, thanks for raising this! Direct instantiation of HelpFormatter should continue to work. I think the fix is to call self._set_color(False) at the end of __init__ to initialize _theme with a no-color default. The parser can still override it afterward. I've put up #142384 to address this.

@hamdanal And thank you for testing the nightly and reporting so quickly :)

Beware, this also breaks existing code that sets the color this way.

This was possible in 3.14 and now it explodes:

Python 3.14.2 (main, Dec  5 2025, 00:00:00) [GCC 15.2.1 20251111 (Red Hat 15.2.1-4)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import argparse
>>> argparse.HelpFormatter(prog='', color=True)
<argparse.HelpFormatter object at 0x7fd998cd1400>

Python 3.15.0a3 (main, Dec 16 2025, 00:00:00) [GCC 15.2.1 20251211 (Red Hat 15.2.1-5)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import argparse
>>> argparse.HelpFormatter(prog='', color=True)
Traceback (most recent call last):
  File "<python-input-1>", line 1, in <module>
    argparse.HelpFormatter(prog='', color=True)
    ~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^
TypeError: HelpFormatter.__init__() got an unexpected keyword argument 'color'

In particular, this breaks pypa/build before pypa/build#962

Reported as #142928, so it is trackable.