Add fast path in distinct()

Author: akx

babel/util.py

@@ -38,6 +38,9 @@ def distinct(iterable: Iterable[_T]) -> Generator[_T, None, None]:
 
     :param iterable: the iterable collection providing the data
     """
+    if isinstance(iterable, (tuple, list)) and len(iterable) <= 1:
+        yield from iterable
+        return
     seen = set()
     for item in iter(iterable):
         if item not in seen:

tests/test_util.py

@@ -31,6 +31,12 @@ class _FF:
 def test_distinct():
     assert list(util.distinct([1, 2, 1, 3, 4, 4])) == [1, 2, 3, 4]
     assert list(util.distinct('foobar')) == ['f', 'o', 'b', 'a', 'r']
+    assert list(util.distinct(c for c in 'foobar')) == ['f', 'o', 'b', 'a', 'r']
+    # Fast path exercises
+    assert list(util.distinct([])) == []
+    assert list(util.distinct(())) == []
+    assert list(util.distinct(('a',))) == ['a']
+    assert list(util.distinct(['a'])) == ['a']
 
 
 def test_pathmatch():