class Permute:
    def __init__(self, l):
        self.list = l
    def __iter__(self):
        if len(self.list) == 0:
            yield self.list
        elif len(self.list) == 1:
            yield self.list
        elif len(self.list) == 2:
            yield self.list
            yield self.list[::-1]
        else:
            for index, element in enumerate(self.list):
                singleList = [element]
                remainderList = self.list[:index] + self.list[index+1:]

                # permute the rest of the list using recursion
                for j in Permute(remainderList):
                    yield singleList + j

def main():
	l = ['a','b','c','d']
	for i in Permute(l):
		print(i)

main()