TypeError: argument of type 'NoneType' is not iterable

Question

I am making a Hangman game in Python. In the game, one python file has a function that selects a random string from an array and stores it in a variable. That variable is then passed to a function in another file. That function stores a users guess as a string in a variable, then checks to see if that guess is in the word. However, whenever I type a letter and press enter, I get the error in the title of this question. Just so you know, I'm using Python 2.7. Here's the code for the function that takes a word:

import random

easyWords = ["car", "dog", "apple", "door", "drum"]

mediumWords = ["airplane", "monkey", "bananana", "window", "guitar"]

hardWords = ["motorcycle", "chuckwalla", "strawberry", "insulation", "didgeridoo"]

wordCount = []

#is called if the player chooses an easy game. 
#The words in the array it chooses are the shortest.
#the following three functions are the ones that
#choose the word randomly from their respective arrays.
def pickEasy():
    word = random.choice(easyWords)
    word = str(word)
    for i in range(1, len(word) + 1):
        wordCount.append("_")

#is called when the player chooses a medium game.
def pickMedium():
    word = random.choice(mediumWords)
    for i in range(1, len(word) + 1):
        wordCount.append("_")

#is called when the player chooses a hard game. 
def pickHard():
    word = random.choice(hardWords)
    for i in range(1, len(word) + 1):
        wordCount.append("_")

Now here is the code that takes the users guess and determines whether or not it is in the word chosen for the game (Pay no attention to the wordCount variable. Also, "words" is the name of the file with the code above.)):

from words import *
from art import *

def gamePlay(difficulty):
    if difficulty == 1:
        word = pickEasy()
        print start
        print wordCount
        getInput(word)

    elif difficulty == 2:
        word = pickMedium()
        print start
        print wordCount

    elif difficulty == 3:
        word = pickHard()
        print start
        print wordCount

def getInput(wordInput):
    wrong = 0
    guess = raw_input("Type a letter to see if it is in the word: \n").lower()

    if guess in wordInput:
        print "letter is in word"

    else:
        print "letter is not in word"

So far I have tried converting the "guess" variable in the gamePlay function to a string with str(), I've tried making it lowercase with .lower(), and I've done similar things in the words file. Here is the full error I get when I run this:

File "main.py", line 42, in <module>
    main()
  File "main.py", line 32, in main
    diff()
  File "main.py", line 17, in diff
    gamePlay(difficulty)
  File "/Users/Nathan/Desktop/Hangman/gameplay.py", line 9, in gamePlay
    getInput(word)
  File "/Users/Nathan/Desktop/Hangman/gameplay.py", line 25, in getInput
    if guess in wordInput:

The "main.py" you see is another python file I wrote. If you would like to see the others let me know. However, I feel the ones I've shown are the only important ones. Thank you for your time! Let me know if I left out any important details.

Answer 1

If a function does not return anything, e.g.:

def test():
    pass

it has an implicit return value of None.

Thus, as your pick* methods do not return anything, e.g.:

def pickEasy():
    word = random.choice(easyWords)
    word = str(word)
    for i in range(1, len(word) + 1):
        wordCount.append("_")

the lines that call them, e.g.:

word = pickEasy()

set word to None, so wordInput in getInput is None. This means that:

if guess in wordInput:

is the equivalent of:

if guess in None:

and None is an instance of NoneType which does not provide iterator/iteration functionality, so you get that type error.

The fix is to add the return type:

def pickEasy():
    word = random.choice(easyWords)
    word = str(word)
    for i in range(1, len(word) + 1):
        wordCount.append("_")
    return word