Issue #4615. Document how to use itertools for de-duping.
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
index db38e69..348c264 100644
--- a/Doc/library/itertools.rst
+++ b/Doc/library/itertools.rst
@@ -687,3 +687,27 @@
return
indices[i:] = [indices[i] + 1] * (r - i)
yield tuple(pool[i] for i in indices)
+
+ 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 iterable:
+ if element not in seen:
+ seen_add(element)
+ yield element
+ else:
+ for element in iterable:
+ k = key(element)
+ if k not in seen:
+ seen_add(k)
+ yield element
+
+ def unique_justseen(iterable, key=None):
+ "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
+ return imap(next, imap(itemgetter(1), groupby(iterable, key)))