Fix py37-38 structuring of mixed typing/regular generics

Author: bibajz

HISTORY.rst

@@ -7,6 +7,8 @@ History
 * ``attrs`` and dataclass structuring is now ~25% faster.
 * Fix an issue structuring bare ``typing.List`` s on Pythons lower than 3.9.
   (`#209 <https://github.com/python-attrs/cattrs/issues/209>`_)
+* Fix structuring bare generics on Pythons lower than 3.9.
+  (`https://github.com/python-attrs/cattrs/issues/218`)
 
 1.10.0 (2022-01-04)
 -------------------

src/cattr/_compat.py

@@ -168,13 +168,15 @@ def is_mapping(type):
     bare_mutable_seq_args = TypingMutableSequence.__args__
 
     def is_bare(type):
-        args = type.__args__
+        # Lower-cased generics in 3.7-8 do not have `__args__` attribute.
+        args = getattr(type, "__args__", None)
         return (
             args == bare_list_args
             or args == bare_seq_args
             or args == bare_mapping_args
             or args == bare_dict_args
             or args == bare_mutable_seq_args
+            or args is None
         )
 
     def is_counter(type):