E721: pycodestyle v2.11.0 does not raise the error to int == type(obj)

[ftnext]

Environment

% python -V
Python 3.11.4
% pycodestyle --version
2.11.0

% pip list
Package     Version
----------- -------
pip         23.2.1
pycodestyle 2.11.0
setuptools  68.0.0

Normal behavior

% cat example.py
if type(obj) == int:
    pass
% pycodestyle example.py
example.py:1:4: E721 do not compare types, for exact checks use `is` / `is not`, for instance checks use `isinstance()`

Great!

Strange behavior

Change type(obj) == int to int == type(obj) (swap the left and right sides).

Expected

Raise E721.
This code is still comparing the return value of type.

Actual

Do NOT raise E721.

% cat example.py
if int == type(obj):
    pass
% pycodestyle example.py
% echo $?
0

Investigation

>>> from pycodestyle import comparison_type
>>> list(comparison_type("if type(obj) == int:", noqa=False))
[(3, 'E721 do not compare types, for exact checks use `is` / `is not`, for instance checks use `isinstance()`')]
>>> list(comparison_type("if int == type(obj):", noqa=False))
[]

In v2.11.0 (21abd9b), COMPARE_TYPE_REGEX has 2 captures.

pycodestyle/pycodestyle.py

Lines 128 to 131 in 21abd9b

	COMPARE_TYPE_REGEX = re.compile(
	r'[=!]=\s+type(?:\s*\(\s*([^)]*[^ )])\s*\))'
	r'|\btype(?:\s*\(\s*([^)]*[^ )])\s*\))\s+[=!]='
	)

In comparison_type, the first captured substring is only referred (inst = match.group(1)).

pycodestyle/pycodestyle.py

Lines 1451 to 1452 in 21abd9b

	@register_check
	def comparison_type(logical_line, noqa):

pycodestyle/pycodestyle.py

Lines 1461 to 1470 in 21abd9b

	match = COMPARE_TYPE_REGEX.search(logical_line)
	if match and not noqa:
	inst = match.group(1)
	if inst and inst.isidentifier() and inst not in SINGLETONS:
	return # Allow comparison for types which are not obvious
	yield (
	match.start(),
	"E721 do not compare types, for exact checks use `is` / `is not`, "
	"for instance checks use `isinstance()`",
	)

>>> from pycodestyle import COMPARE_TYPE_REGEX
>>> from pycodestyle import SINGLETONS

>>> match = COMPARE_TYPE_REGEX.search("if type(obj) == int:")
>>> match
<re.Match object; span=(3, 15), match='type(obj) =='>
>>> match.group(1)  # None; Go yield (L1466)
>>> match.group(2)
'obj'

>>> match = COMPARE_TYPE_REGEX.search("if int == type(obj):")
>>> match
<re.Match object; span=(7, 19), match='== type(obj)'>
>>> match.group(1)
'obj'
>>> match.group(2)
>>> inst = match.group(1)
>>> inst and inst.isidentifier() and inst not in SINGLETONS  # Go return (L1465) not yield
True

If you need to use captured substrings, you might need to do something like inst = match.group(1) or match.group(2).
However, in that case, inst and inst.isidentifier() and inst not in SINGLETONS would return True, and E721 would no longer be raised.
Therefore, I believe that removing the return statement here would resolve the reported issue.

One concern I have is that it seems inst = match.group(1) has not been changed along with the last pull request.
https://github.com/PyCQA/pycodestyle/pull/1086/files
Depending on the reason for not changing this, we might need to consider a different solution.