From 30ca0f06b9891e5bd3cb2ee9ac7c88d42d8d8675 Mon Sep 17 00:00:00 2001
From: Apoorv Darshan <ad13dtu@gmail.com>
Date: Thu, 9 Jul 2026 19:26:44 +0530
Subject: [PATCH] E721: flag swapped type comparisons like `int == type(obj)`

E721 only fired when a `type(...)` call was on the left-hand side of
`==` / `!=` (e.g. `type(obj) == int`). The swapped form
`int == type(obj)` was silently ignored even though it is the same
type comparison.

`comparison_type` only inspected `match.group(1)`, the argument of the
right-hand `type(...)` call, and suppressed the warning whenever that
argument was a plain identifier. Because the two regex alternatives
capture opposite sides, this made the check asymmetric: `type(obj) == x`
was reported but the mirror `x == type(obj)` was not.

Remove the identifier-based suppression so both operand orders are
treated identically, and drop the now-unused capture groups from
COMPARE_TYPE_REGEX. Add regression fixtures for the swapped `==` and
`!=` forms to testing/data/E72.py.

Fixes #1187.
---
 pycodestyle.py      | 9 ++++-----
 testing/data/E72.py | 6 ++++++
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/pycodestyle.py b/pycodestyle.py
index 868e79d5..e53e8b0d 100755
--- a/pycodestyle.py
+++ b/pycodestyle.py
@@ -121,8 +121,8 @@
 COMPARE_NEGATIVE_REGEX = re.compile(r'\b(?<!is\s)(not)\s+[^][)(}{ ]+\s+'
                                     r'(in|is)\s')
 COMPARE_TYPE_REGEX = re.compile(
-    r'[=!]=\s+type(?:\s*\(\s*([^)]*[^\s)])\s*\))'
-    r'|(?<!\.)\btype(?:\s*\(\s*([^)]*[^\s)])\s*\))\s+[=!]='
+    r'[=!]=\s+type(?:\s*\(\s*[^)]*[^\s)]\s*\))'
+    r'|(?<!\.)\btype(?:\s*\(\s*[^)]*[^\s)]\s*\))\s+[=!]='
 )
 KEYWORD_REGEX = re.compile(r'(\s*)\b(?:%s)\b(\s*)' % r'|'.join(KEYWORDS))
 OPERATOR_REGEX = re.compile(r'(?:[^,\s])(\s*)(?:[-+*/|!<=>%&^]+|:=)(\s*)')
@@ -1498,12 +1498,11 @@ def comparison_type(logical_line, noqa):
     Okay: if isinstance(obj, int):
     Okay: if type(obj) is int:
     E721: if type(obj) == type(1):
+    E721: if type(obj) == int:
+    E721: if int == type(obj):
     """
     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`, "
diff --git a/testing/data/E72.py b/testing/data/E72.py
index 5d1046cb..d74350e8 100644
--- a/testing/data/E72.py
+++ b/testing/data/E72.py
@@ -4,6 +4,12 @@
 #: E721
 if type(res) != type(""):
     pass
+#: E721
+if int == type(res):
+    pass
+#: E721
+if str != type(res):
+    pass
 #: Okay
 res.type("") == ""
 #: Okay