1 files changed, 18 insertions, 1 deletions
diff --git a/itertoolset.py b/itertoolset.py
index 13bb896..ae4be8a 100644
--- a/itertoolset.py
+++ b/itertoolset.py
@@ -1,4 +1,4 @@
-from itertools import cycle, islice
+from itertools import *
 
 def roundrobin(*iterables):
     """roundrobin('ABC', 'D', 'EF') --> A D E B F C"""
@@ -11,3 +11,20 @@ def roundrobin(*iterables):
         except StopIteration:
             pending -= 1
             nexts = cycle(islice(nexts, pending))
+
+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 ifilterfalse(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