| from itertools import filterfalse | |
| 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 filterfalse(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 | |