Reverted "Fixed #35564 -- Improved readability of subclass identification."

This reverts commit f0d05a747f7a099e6c6bc58c42a787546d2212e7 due to a performance regression.

django/contrib/admin/checks.py

@@ -1,5 +1,4 @@
 import collections
-import contextlib
 from itertools import chain
 
 from django.apps import apps
@@ -22,8 +21,9 @@ def _issubclass(cls, classinfo):
     issubclass() variant that doesn't raise an exception if cls isn't a
     class.
     """
-    with contextlib.suppress(TypeError):
+    try:
         return issubclass(cls, classinfo)
+    except TypeError:
         return False
 
 
@@ -34,8 +34,12 @@ def _contains_subclass(class_path, candidate_paths):
     """
     cls = import_string(class_path)
     for path in candidate_paths:
-        with contextlib.suppress(ImportError, TypeError):
-            if issubclass(import_string(path), cls):
+        try:
+            candidate_cls = import_string(path)
+        except ImportError:
+            # ImportErrors are raised elsewhere.
+            continue
+        if _issubclass(candidate_cls, cls):
             return True
     return False
 

django/contrib/auth/checks.py

@@ -1,4 +1,3 @@
-import contextlib
 from itertools import chain
 from types import MethodType
 
@@ -16,10 +15,13 @@ def _subclass_index(class_path, candidate_paths):
     list of candidate paths. If it does not exist, return -1.
     """
     cls = import_string(class_path)
-    for i, path in enumerate(candidate_paths):
-        with contextlib.suppress(ImportError, TypeError):
-            if issubclass(import_string(path), cls):
-                return i
+    for index, path in enumerate(candidate_paths):
+        try:
+            candidate_cls = import_string(path)
+            if issubclass(candidate_cls, cls):
+                return index
+        except (ImportError, TypeError):
+            continue
     return -1