itercools.py 文件源码

def unique(*iterables, key=None):
    """Yield unique elements, preserving order.

    >>> ''.join(unique('AAAABBBCCDAABBB'))
    'ABCD'
    >>> ''.join(unique('AAAA', 'BBBC', 'CDA', 'ABBB'))
    'ABCD'
    >>> ''.join(unique('ABBCcAD', key=str.casefold))
    'ABCD'
    """
    combined = chain.from_iterable(iterables)
    yielded = set()
    # Avoid inner-loop name lookups
    already_yielded = yielded.__contains__
    remember = yielded.add

    if key is None:
        for element in filterfalse(already_yielded, combined):
            remember(element)
            yield element

    else:
        for element in combined:
            k = key(element)
            if not already_yielded(k):
                remember(k)
                yield element