Filter out redundant entries in zip_children. Closes #117.

Author: jaraco

importlib_metadata/__init__.py

@@ -28,6 +28,7 @@
     MetaPathFinder,
     email_message_from_string,
     PyPy_repr,
+    unique_ordered,
     )
 from importlib import import_module
 from itertools import starmap
@@ -425,7 +426,7 @@ def zip_children(self):
         names = zip_path.root.namelist()
         self.joinpath = zip_path.joinpath
 
-        return (
+        return unique_ordered(
             posixpath.split(child)[0]
             for child in names
             )

importlib_metadata/_compat.py

@@ -15,9 +15,11 @@
     NotADirectoryError = builtins.NotADirectoryError
     PermissionError = builtins.PermissionError
     map = builtins.map
+    from itertools import filterfalse
 else:  # pragma: nocover
     from backports.configparser import ConfigParser
     from itertools import imap as map  # type: ignore
+    from itertools import ifilterfalse as filterfalse
     import contextlib2 as contextlib
     FileNotFoundError = IOError, OSError
     IsADirectoryError = IOError, OSError
@@ -131,3 +133,18 @@ def make_param(name):
     if affected:  # pragma: nocover
         __repr__ = __compat_repr__
     del affected
+
+
+# from itertools recipes
+def unique_everseen(iterable):
+    "List unique elements, preserving order. Remember all elements ever seen."
+    seen = set()
+    seen_add = seen.add
+
+    for element in filterfalse(seen.__contains__, iterable):
+        seen_add(element)
+        yield element
+
+
+unique_ordered = (
+    unique_everseen if sys.version_info < (3, 7) else dict.fromkeys)