Optimize unique_justseen() recipe for a common case. (pythongh-113147)

AlexWaygood · Dec 14, 2023 · 5f7d735 · 5f7d735
1 parent 25061f5
commit 5f7d735
Showing 1 changed file with 2 additions and 0 deletions.
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
@@ -1017,6 +1017,8 @@ which incur interpreter overhead.
        "List unique elements, preserving order. Remember only the element just seen."
        # unique_justseen('AAAABBBCCDAABBB') --> A B C D A B
        # unique_justseen('ABBcCAD', str.lower) --> A B c A D
+       if key is None:
+           return map(operator.itemgetter(0), groupby(iterable))
        return map(next, map(operator.itemgetter(1), groupby(iterable, key)))