gen3.py

def permute(a):
    """
    Permutes a list
    """
    def toString(a):
        return ''.join(a)
    
    #Keep track of what we've outputted so we don't produce non-unqiue permutations
    _current = set()
    def merge(c, lists):
        """
        This is the main generator that we use for this example
        """
        for temp in lists:
            for i in range(0, len(temp) + 1):
                #Pushing the letter in between the indices
                perm = toString(temp[:i]) + c + toString(temp[i:])
                if(perm not in _current):
                    _current.add(perm)
                    yield perm
    # Base case of 1 element list
    if(len(a) == 1):
        return [a]
    # Base case of 2 element list
    if(len(a) == 2):
        return [a[0] + a[1],a[1] +a[0]]
    else:
        # The algorithm works by pulling out each letter from the string and then
        # inserting it at every point in the string to get a list of permutations
        for i in range(0, len(a)):
            _h = a
            _c = _h.pop(i) 
            #Return the generator object!
            return merge(_c,permute(_h))
            

l = permute(list("abcde"))
for perm in l:
    print (perm)
    input()