`can_colorize()` ignores `FORCE_COLOR`/`NO_COLOR`/`TERM` when `-E` is set

[hugovk]

Bug report

Bug description:

Using one of the FORCE_COLOR, NO_COLOR or TERM=dumb environment variables is ignored when you use Python with -E.

• https://docs.python.org/3/using/cmdline.html#using-on-controlling-color

-E means:

Ignore all PYTHON* environment variables, e.g. PYTHONPATH and PYTHONHOME, that might be set.

• https://docs.python.org/3/using/cmdline.html#cmdoption-E

The -E is stored in sys.flags.ignore_environment.

• https://docs.python.org/3/library/sys.html#sys.flags.ignore_environment

sys.flags.ignore_environment is used to ignore PYTHON_COLORS (correct) but it's also ignoring these other env vars (incorrect).

For example, this is not colourised, as expected:

❯ NO_COLOR=1 python3.13 -c 1/0
Traceback (most recent call last):
 File "<string>", line 1, in <module>
 1/0
 ~^~
ZeroDivisionError: division by zero

However, NO_COLOR=1 is ignored when passing -E and the output has colour when it should not:

❯ NO_COLOR=1 python3.13 -E -c 1/0
Traceback (most recent call last):
 File "<string>", line 1, in <module>
 1/0
 ~^~
ZeroDivisionError: division by zero

This bit needs updating:

cpython/Lib/_colorize.py

Lines 43 to 56 in 487fdbe

	if not sys.flags.ignore_environment:
	if os.environ.get("PYTHON_COLORS") == "0":
	return False
	if os.environ.get("PYTHON_COLORS") == "1":
	return True
	if "NO_COLOR" in os.environ:
	return False
	if not COLORIZE:
	return False
	if not sys.flags.ignore_environment:
	if "FORCE_COLOR" in os.environ:
	return True
	if os.environ.get("TERM") == "dumb":
	return False

CPython versions tested on:

3.13, 3.14

Operating systems tested on:

Linux, macOS, Windows

Linked PRs

• gh-127873: Only check sys.flags.ignore_environment for PYTHON* env vars #127877
• [3.13] gh-127873: Only check sys.flags.ignore_environment for PYTHON* env vars (GH-127877) #129138