Whitelist classes in collections.abc as valid interface types.

pure_interface/interface.py

@@ -168,6 +168,8 @@ def _type_is_interface(cls: type) -> bool:
     """Return True if cls is a pure interface or an empty ABC class"""
     if cls is object:
         return False
+    if cls.__module__ == "collections.abc":
+        return True
     if hasattr(cls, "_pi"):
         return cls._pi.type_is_interface
     if cls is Generic:

tests/test_no_content_checks.py

@@ -3,6 +3,7 @@
 # --------------------------------------------------------------------------------------------
 
 import abc
+import collections.abc
 import unittest
 
 import pure_interface
@@ -106,3 +107,8 @@ class IAnimal(pure_interface.Interface):
                 @property
                 def height(self):
                     return self
+
+    def test_std_lib_abc_passes(self):
+
+        class ITest(collections.abc.Sized, pure_interface.Interface):
+            pass