ocaml 99 problems #26 in python

99_problems_26.py

tab_depth = 0


def log(s=None, **kwargs):
    global tab_depth
    msg = s if s is not None else ", ".join(["{} == {}".format(k, v) for k, v in kwargs.items()])
    print("\t" * tab_depth + msg)

def perms(n, l):
    global tab_depth

    log(n=n, l=l)
    if n <= 0:
        log(s="returning [ [] ]")
        return [ [] ]
    else:
        if len(l) == 0:
            log(s="returning []")
            return []
        h = l[0]
        tl = l[1:]
        log(h=h, tl=tl)

        tab_depth += 1
        with_h = list(map(lambda l: [h] + l, perms(n-1, tl)))
        without_h = perms(n, tl)
        tab_depth -= 1
        return with_h + without_h

# Without debugging
def perms_(n, l):
    if n <= 0:
        return [ [] ]
    else:
        if len(l) == 0:
            return []
        h = l[0]
        tl = l[1:]
        with_h = list(map(lambda l: [h] + l, perms_(n-1, tl)))
        without_h = perms_(n, tl)
        return with_h + without_h

print(perms(2, ["a", "b", "c", "d"]))

"""
➜  /tmp python test.py
n == 2, l == ['a', 'b', 'c', 'd']
h == a, tl == ['b', 'c', 'd']
	n == 1, l == ['b', 'c', 'd']
	h == b, tl == ['c', 'd']
		n == 0, l == ['c', 'd']
		returning [ [] ]
		n == 1, l == ['c', 'd']
		h == c, tl == ['d']
			n == 0, l == ['d']
			returning [ [] ]
			n == 1, l == ['d']
			h == d, tl == []
				n == 0, l == []
				returning [ [] ]
				n == 1, l == []
				returning []
	n == 2, l == ['b', 'c', 'd']
	h == b, tl == ['c', 'd']
		n == 1, l == ['c', 'd']
		h == c, tl == ['d']
			n == 0, l == ['d']
			returning [ [] ]
			n == 1, l == ['d']
			h == d, tl == []
				n == 0, l == []
				returning [ [] ]
				n == 1, l == []
				returning []
		n == 2, l == ['c', 'd']
		h == c, tl == ['d']
			n == 1, l == ['d']
			h == d, tl == []
				n == 0, l == []
				returning [ [] ]
				n == 1, l == []
				returning []
			n == 2, l == ['d']
			h == d, tl == []
				n == 1, l == []
				returning []
				n == 2, l == []
				returning []
[['a', 'b'], ['a', 'c'], ['a', 'd'], ['b', 'c'], ['b', 'd'], ['c', 'd']]
"""