Permutations in Python

permutations.py

# coding=utf-8

import copy
import datetime

term = 'abcdefghij'
o = 0


def permutations(tokens, p, n):
    global o
    o += 1
    if 1 == n:
        p.append([tokens[0]])
    else:
        new_permutations = []

        for i in range(len(p)):
            o += 1
            permutation = p[i]
            new_permutations.append(permutation)
            for j in range(1, n):
                o += 1
                new_permutations.append(copy.copy(permutation))

        p = new_permutations

        token = tokens[n-1]
        index = -1
        for permutation in p:
            o += 1
            index += 1
            permutation.insert(index % n, token)

    if len(tokens) <= n:
        return p
    else:
        return permutations(tokens, p, n+1)

t_start = datetime.datetime.now()
p = permutations([token for token in term], [], 1)
t_end = datetime.datetime.now()
t = t_end - t_start

print("O(%d) = %d") % (len(term), o)
print("t = %.2fms") % (t.microseconds / 1000.0)
#for permutation in p:
#    print(''.join(permutation))