“当代码适用于其他人时，'NoneType'对象不可迭代”。 我怎么弄清楚什么是错的？

Question

I'm following a guided project in Python and there's code I wrote that seems to align with the solution, however, I'm getting an error while they did not.

I saw online that a return statement might be needed but the solution doesn't use one and no matter where I place the return, I get an error anyway.

"displayfreq" is a code I defined above in the code; it produces a sorted frequency table.

genres_ios = displayfreq(ios_free, -5)

for genre in genres_ios:
    total = 0
    len_genre = 0

    for app in ios_free:
        genre_app = app[-5]
        if genre_app == genre:
            tot_ratings = float(app[5])
            total += tot_ratings
            len_genre += 1
    avg_tot_rating = total / len_genre
    print(genre, 'with average total rating of', avg_tot_ratings)

I expected to see the average number of ratings per genre, but instead, I'm getting,

"TypeError: 'NoneType' object is not iterable"

for the line "for genre in genres_ios"

Answer 1

A return statement is needed in displayfreq() , or it will return None . Because genres_ios is None , you cannot iterate over it and you get the error.

If it works on other machines, displayfreq() might not work for your machine.

Answer 2

As you specified that you are getting "TypeError: 'NoneType' object is not iterable" for the line " for genre in genres_ios: ...", it means that the variable genres_ios is having value None and thus you are getting such an error.

For this, you need to return the variable or expression of your sorted frequency table.

Also note that in the function displayfreq, you are not manipulating the ios_free variable or you would have the value of ios_free changed. If you want a copy of ios_free use ios_free.copy() .