Compute the Inverse of a Permutation in F_2^n

Inv.py

import math

def isPerm(x):
	if math.log(len(x), 2)% 1 != 0:
		return False

	for i in range(len(x)):
		try:
			x.index(i)
		except ValueError:
			return False
	return True
	

def inv(x):
	finv = [ 0 for i in range(len(x)) ]	
	for i in range(len(x)):
		finv[f[i]] = i;
	return finv
	
	
if __name__ == '__main__':

	f = [1,3,2,0]
	if isPerm(f):
		print inv(f)
	else:
		print 'Not a Permutation!'