compatibility.py 文件源码

def combinations_with_replacement(iterable, r):
        """Return r length subsequences of elements from the input iterable
        allowing individual elements to be repeated more than once.

        Combinations are emitted in lexicographic sort order. So, if the
        input iterable is sorted, the combination tuples will be produced
        in sorted order.

        Elements are treated as unique based on their position, not on their
        value. So if the input elements are unique, the generated combinations
        will also be unique.

        See also: combinations

        Examples
        ========

        >>> from sympy.core.compatibility import combinations_with_replacement
        >>> list(combinations_with_replacement('AB', 2))
        [('A', 'A'), ('A', 'B'), ('B', 'B')]
        """
        pool = tuple(iterable)
        n = len(pool)
        if not n and r:
            return
        indices = [0] * r
        yield tuple(pool[i] for i in indices)
        while True:
            for i in reversed(range(r)):
                if indices[i] != n - 1:
                    break
            else:
                return
            indices[i:] = [indices[i] + 1] * (r - i)
            yield tuple(pool[i] for i in indices)