When resolving entry points globally, only expose entry points for unique distributions. Fixes #280.

Author: jaraco

.coveragerc

@@ -3,6 +3,7 @@ omit =
 	*/.tox/*
 	tests/*
 	prepare/*
+	*/_itertools.py
 
 [report]
 show_missing = True

importlib_metadata/__init__.py

@@ -19,6 +19,8 @@
     Protocol,
 )
 
+from ._itertools import unique_everseen
+
 from configparser import ConfigParser
 from contextlib import suppress
 from importlib import import_module
@@ -646,7 +648,10 @@ def entry_points():
 
     :return: EntryPoint objects for all installed packages.
     """
-    eps = itertools.chain.from_iterable(dist.entry_points for dist in distributions())
+    unique = functools.partial(unique_everseen, key=operator.attrgetter('name'))
+    eps = itertools.chain.from_iterable(
+        dist.entry_points for dist in unique(distributions())
+    )
     by_group = operator.attrgetter('group')
     ordered = sorted(eps, key=by_group)
     grouped = itertools.groupby(ordered, by_group)

importlib_metadata/_itertools.py

@@ -0,0 +1,19 @@
+from itertools import filterfalse
+
+
+def unique_everseen(iterable, key=None):
+    "List unique elements, preserving order. Remember all elements ever seen."
+    # unique_everseen('AAAABBBCCDAABBB') --> A B C D
+    # unique_everseen('ABBCcAD', str.lower) --> A B C D
+    seen = set()
+    seen_add = seen.add
+    if key is None:
+        for element in filterfalse(seen.__contains__, iterable):
+            seen_add(element)
+            yield element
+    else:
+        for element in iterable:
+            k = key(element)
+            if k not in seen:
+                seen_add(k)
+                yield element