why will I get a "TypeError: object of type 'NoneType' has no len()"?

Question

words = [ 'look', 'into', 'my', 'eyes', 'look', 'into', 'my', 'eyes', 'the', 'eyes', 'the', 'eyes', 'the', 'eyes', 'not', 'around', 'the', 'eyes',"don't", 'look', 'around', 'the', 'eyes', 'look', 'into', 'my', 'eyes', "you're", 'under']

def requirement(word):
    onelist = []
    if word in words:
        return(len(onelist.append(word)))


print(map(requirement('look'), words))

Error

TypeError: object of type 'NoneType' has no len()

I want to practise the function "map". But it seems that I made a mistake when I use len().

You're calling `len` on the function `list.append`, not on `onelist`.You ned to separate the `list.append` call from the `len` call. — Daniel, Oct 24 '17 at 15:49
@Coal_ Just out of curiosity, how did you have an encoded apostrophe end up in the comment? — Carcigenicate, Oct 24 '17 at 15:51

score 2 · Answer 1 · answered Oct 24 '17 at 15:50

The function list.append() modifies a list in place and returns None. So the line

return(len(onelist.append(word)))

is trying to return the length of None, which should obviously throw a TypeError. Try something like

onelist.append(word)
return(len(onelist))

why will I get a "TypeError: object of type 'NoneType' has no len()"?

1 Answers1