Python mysterious error

Question

So I am working on a program to create portmanteaus. I have the code and functions I need, and I have put them together.

Here is the code:

def portmanteauscore(start, mid, end):
 totallen = len(start) + len(mid) + len(end)
 return totallen - abs((len(start)/totallen) - len(start)) - abs((len(mid)/totallen) - len(mid)) - abs((len(end)/totallen) - len(end))
def portmanteaugenerator(word1, word2, words):
 mid = longest_common_substring(word1, word2)
 start = word1[:word1.index(mid)]
 end = word2[len(mid):]
 if start + mid in words and mid + end in words:
 return start, mid, end
def natalie(words):
 "Find the best Portmanteau word formed from any two of the list of words."
 wordpermutations = list(itertools.permutations(words))
 maxscore, bestnatalie = 0, ''
 for perm in wordpermutations:
 start, mid, end = portmanteaugenerator(perm[0], perm[1], words)
 if portmanteauscore(start, mid, end) > maxscore:
 bestnatalie, maxscore = start + mid + end, portmanteauscore(start, mid, end)
 print bestnatalie
 return bestnatalie
def longest_common_substring(s1, s2):
 m = [[0] * (1 + len(s2)) for i in xrange(1 + len(s1))]
 longest, x_longest = 0, 0
 for x in xrange(1, 1 + len(s1)):
 for y in xrange(1, 1 + len(s2)):
 if s1[x - 1] == s2[y - 1]:
 m[x][y] = m[x - 1][y - 1] + 1
 if m[x][y] > longest:
 longest = m[x][y]
 x_longest = x
 else:
 m[x][y] = 0
 return s1[x_longest - longest: x_longest]

But when I run the code, I keep getting this error message,

Traceback (most recent call last):
 File "vm_main.py", line 33, in <module>
 import main
 File "/tmp/vmuser_ijxrjleuxj/main.py", line 107, in <module>
 print test_natalie()
 File "/tmp/vmuser_ijxrjleuxj/main.py", line 87, in test_natalie
assert natalie(['adolescent', 'scented', 'centennial', 'always', 'ado']) in ('adolescented','adolescentennial')
 File "/tmp/vmuser_ijxrjleuxj/main.py", line 67, in natalie
 start,mid,end=portmanteaugenerator(perm[0],perm[1],words)
 TypeError: 'NoneType' object is not iterable

This occurs when I return the start,mid,and end variables for the portmanteau generator. When given a list of words, it should return a portmanteau from two words that is the best according to portmanteau score.

But I keep getting this type error for some reason. I have tried making start,mid,end a list and it still fails to run. Can you please help me?

• user2357112: More spaces! Spaces after commas and around binary operators would make this a lot more readable.
• icedwater: Ironic when talking about a portmanteaugenerator ;)

Answer 1

Most likely, start+mid in words and mid+end in words returns False and so the function, instead of passing through the if-statement, returns None (because if a function does not return something, it defaults to None).

Then you're trying to do something like:

start,mid,end = None

What python is trying to do is split up None in those three variables. It's like doing this:

one, two, three = (1, 2, 3)

But you can't, because None is not an iterable.