utils.py 文件源码

def unique_everseen(iterable, key=None):
    """List unique elements, preserving order. Remember all elements ever seen.

    The snippet is taken form https://docs.python.org/3.6/library/itertools.html#itertools-recipes
    >>> 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