combinations of letters using itertools in python2.7

Question

I am trying to use itertools.combinations to return all the combinations of letters in alphabet with length at most n.

def string_combinations(alphabet, n):
    '''
    Parameters
    ----------
    alphabet : {str}
    n : {int}

    Returns
    -------
    list : {list} of {str}    

    Example
    -------
    >>> string_combinations('abc', 2)
    ['a', 'b', 'c', 'ab', 'ac', 'bc']
    '''

So far I have

return [str(x) for i in range(1,n+1) for x in itertools.combinations(alphabet,i)]

but itertools.combinations returns tuples in a list [('a',), ('b',), ('c',), ('a', 'b'), ('a', 'c'), ('b', 'c')] How should I achieve my desired solution?

Answer 1

You can concatenate all the strings returned by itertools :

result = map("".join, (comb for i in range(1, n+1) for comb in itertools.combinations(alphabet, i)))

This is equivalent to putting a call to "".join inside a list comprehension:

result = ["".join(comb) for ...]

"".join(iterable) concatenates all the string that are retrieved from an iterable:

"".join(('a', 'b', 'c')) == "abc"