Prioritize valid dists to invalid dists when retrieving by name.

Closes #489

Author: jaraco

importlib_metadata/__init__.py

@@ -25,7 +25,7 @@
     install,
 )
 from ._functools import method_cache, pass_none
-from ._itertools import always_iterable, unique_everseen
+from ._itertools import always_iterable, bucket, unique_everseen
 from ._meta import PackageMetadata, SimplePath
 
 from contextlib import suppress
@@ -388,7 +388,7 @@ def from_name(cls, name: str) -> Distribution:
         if not name:
             raise ValueError("A distribution name is required.")
         try:
-            return next(iter(cls.discover(name=name)))
+            return next(iter(cls._prefer_valid(cls.discover(name=name))))
         except StopIteration:
             raise PackageNotFoundError(name)
 
@@ -412,6 +412,16 @@ def discover(
             resolver(context) for resolver in cls._discover_resolvers()
         )
 
+    @staticmethod
+    def _prefer_valid(dists: Iterable[Distribution]) -> Iterable[Distribution]:
+        """
+        Prefer (move to the front) distributions that have metadata.
+
+        Ref python/importlib_resources#489.
+        """
+        buckets = bucket(dists, lambda dist: bool(dist.metadata))
+        return itertools.chain(buckets[True], buckets[False])
+
     @staticmethod
     def at(path: str | os.PathLike[str]) -> Distribution:
         """Return a Distribution for the indicated metadata path.

importlib_metadata/_itertools.py

@@ -1,3 +1,4 @@
+from collections import defaultdict, deque
 from itertools import filterfalse
 
 
@@ -71,3 +72,100 @@ def always_iterable(obj, base_type=(str, bytes)):
         return iter(obj)
     except TypeError:
         return iter((obj,))
+
+
+# Copied from more_itertools 10.3
+class bucket:
+    """Wrap *iterable* and return an object that buckets the iterable into
+    child iterables based on a *key* function.
+
+        >>> iterable = ['a1', 'b1', 'c1', 'a2', 'b2', 'c2', 'b3']
+        >>> s = bucket(iterable, key=lambda x: x[0])  # Bucket by 1st character
+        >>> sorted(list(s))  # Get the keys
+        ['a', 'b', 'c']
+        >>> a_iterable = s['a']
+        >>> next(a_iterable)
+        'a1'
+        >>> next(a_iterable)
+        'a2'
+        >>> list(s['b'])
+        ['b1', 'b2', 'b3']
+
+    The original iterable will be advanced and its items will be cached until
+    they are used by the child iterables. This may require significant storage.
+
+    By default, attempting to select a bucket to which no items belong  will
+    exhaust the iterable and cache all values.
+    If you specify a *validator* function, selected buckets will instead be
+    checked against it.
+
+        >>> from itertools import count
+        >>> it = count(1, 2)  # Infinite sequence of odd numbers
+        >>> key = lambda x: x % 10  # Bucket by last digit
+        >>> validator = lambda x: x in {1, 3, 5, 7, 9}  # Odd digits only
+        >>> s = bucket(it, key=key, validator=validator)
+        >>> 2 in s
+        False
+        >>> list(s[2])
+        []
+
+    """
+
+    def __init__(self, iterable, key, validator=None):
+        self._it = iter(iterable)
+        self._key = key
+        self._cache = defaultdict(deque)
+        self._validator = validator or (lambda x: True)
+
+    def __contains__(self, value):
+        if not self._validator(value):
+            return False
+
+        try:
+            item = next(self[value])
+        except StopIteration:
+            return False
+        else:
+            self._cache[value].appendleft(item)
+
+        return True
+
+    def _get_values(self, value):
+        """
+        Helper to yield items from the parent iterator that match *value*.
+        Items that don't match are stored in the local cache as they
+        are encountered.
+        """
+        while True:
+            # If we've cached some items that match the target value, emit
+            # the first one and evict it from the cache.
+            if self._cache[value]:
+                yield self._cache[value].popleft()
+            # Otherwise we need to advance the parent iterator to search for
+            # a matching item, caching the rest.
+            else:
+                while True:
+                    try:
+                        item = next(self._it)
+                    except StopIteration:
+                        return
+                    item_value = self._key(item)
+                    if item_value == value:
+                        yield item
+                        break
+                    elif self._validator(item_value):
+                        self._cache[item_value].append(item)
+
+    def __iter__(self):
+        for item in self._it:
+            item_value = self._key(item)
+            if self._validator(item_value):
+                self._cache[item_value].append(item)
+
+        yield from self._cache.keys()
+
+    def __getitem__(self, value):
+        if not self._validator(value):
+            return iter(())
+
+        return self._get_values(value)

newsfragments/489.feature.rst

@@ -0,0 +1 @@
+Prioritize valid dists to invalid dists when retrieving by name.

tests/test_main.py

@@ -140,7 +140,6 @@ def make_pkg(name, files=dict(METADATA="VERSION: 1.0")):
             f'{name}.dist-info': files,
         }
 
-    @__import__('pytest').mark.xfail(reason="#489")
     def test_valid_dists_preferred(self):
         """
         Dists with metadata should be preferred when discovered by name.