#!/usr/bin/env python
# -*- coding: utf-8 -*-


def compositions(l, init=None):

    # Use init argument or start an empty list (for the first list)
    init = init or []

    yield init

    # Recursion break condition, when there is no more combinations to make
    if len(l) == 0:
        return

    # Iterate through the remaining elements
    for i, v in enumerate(l):

        # Add the element to the list, and create new
        #  combinations with the remaining elements
        for ret in compositions(l[i+1:], init + [v]):
            # replace with "yield from" on Python 3
            yield ret

print(compositions([1, 2, 3]))

# So, in the first call, it will yield the empty list []
# and will iterate through [1, 2, 3, 4]
#
# In the first iteration (element 1), it will add the
#  element to the list and call the function with the
#  remaining elements:
#
#  for ret in compositions([2, 3, 4], [1]):
#
# In this second call, it will yield the list with
#  an single element [1] and will iterate through
#  [2, 3, 4]
#
# In the first iteration (element 2), it will add the
#  element to the list and call the function with the
#  remaining elements:
#
#  for ret in compositions([3, 4], [1, 2]):
#
# And so on...