implement 'util.unique()'

gallery_dl/util.py

@@ -48,12 +48,22 @@ def bdecode(data, alphabet="0123456789"):
 
 
 def advance(iterable, num):
-    """"Advance the iterable by 'num' steps"""
+    """"Advance 'iterable' by 'num' steps"""
     iterator = iter(iterable)
     next(itertools.islice(iterator, num, num), None)
     return iterator
 
 
+def unique(iterable):
+    """Yield unique elements from 'iterable' while preserving order"""
+    seen = set()
+    add = seen.add
+    for element in iterable:
+        if element not in seen:
+            add(element)
+            yield element
+
+
 def raises(cls):
     """Returns a function that raises 'cls' as exception"""
     def wrap(*args):