list comprehension - Name error disappears on print in python -

i trying write code in python generate permutations of input string.

inp = raw_input()  out = [inp[0]] in range(1,len(inp)):    #print [range(len(j)+1) j in out]    out = [j[:k]+inp[i]+j[k:] k in range(len(j)+1) j in out]  print out 

for input 'abc', outputs

traceback (most recent call last): file "perm.py", line 6, in

out = [j[:k]+inp[i]+j[k:] k in range(len(j)+1) j in out]  

nameerror: name 'j' not defined

shell returned 1

if uncomment line 5, , code looks like

inp = raw_input()  out = [inp[0]] in range(1,len(inp)):    print [range(len(j)+1) j in out]    out = [j[:k]+inp[i]+j[k:] k in range(len(j)+1) j in out]  print out 

for input 'abc', outputs

[[0, 1]]

[[0, 1, 2], [0, 1, 2]]

['cba', 'cab', 'bca', 'acb', 'bac','abc']

what sorcery this?

you have list comprehension loops front; need list them in nesting order left right, for j in out needs come first

out = [j[:k]+inp[i]+j[k:] j in out k in range(len(j)+1)] 

the print statement list comprehension defined j name version loop over; in python 2, list comprehension not have own scope for loop target accessible after loop completes regular for loop. has changed in python 3, list comprehensions own scope, dict , set comprehensions , generator expressions.

if helps, write out list comprehensions regular loops first; code did this:

tmp = [] j in out:     tmp.append(range(len(j)+1)) print tmp  out = [] k in range(len(j)+1):     j in out:         out.append(j[:k]+inp[i]+j[k:]) 

where range(len(j)+1) expression only works because have used j for loop target in preceding expression building tmp print.

you may treating coding exercise, standard library includes function produces permutations: itertools.permutations():

from itertools import permutations  inp = raw_input() print list(permutations(inp)) 

demo:

>>> itertools import permutations >>> list(permutations('abc')) [('a', 'b', 'c'), ('a', 'c', 'b'), ('b', 'a', 'c'), ('b', 'c', 'a'), ('c', 'a', 'b'), ('c', 'b', 'a')]