Python for循环未遍历所有项目

Question

I am writing a function that removes all vowels from a word. It looks like this:

def remove_vowels(word):

    vowels = ['a', 'e', 'i', 'o', 'u']

    word = list(word)

    for letter in word:
        print('Looking for letter {}'.format(letter))

        if letter.lower() in vowels:
            try: 
                word.remove(letter)
            except ValueError:
                pass

    return ''.join(word)

I expect it to go through all the letters in the word, check each letter if it is in the vowels array and, if so, remove it.

However, it does not seem that it checks for all letters. For example, for the following call:

print(remove_vowels('perception'))

I am getting the following output:

Looking for letter p
Looking for letter e
Looking for letter c
Looking for letter e
Looking for letter t
Looking for letter i
Looking for letter n
prcpton

For some reason, it skips the r , the second p and the o . I am getting a similar result with other words. Why is this happening?

Answer 1

The reason why it didn't work before is during your for loop you are mutating word which means that it will skip over an iteration whenever you delete something because that deletion resulted in each letter moving up a position. That means that if there was a deletion at position 2 then the next item is now at position 2 and the item after it is in position 3 which is where the next iteration is.

def remove_vowels(word):

    vowels = ['a', 'e', 'i', 'o', 'u']

    word = list(word)
    print(word)
    new_word = []

    for letter in word:
        print('Looking for letter {}'.format(letter))

        if letter.lower() not in vowels:
            try: 
                new_word.append(letter)
            except ValueError:
                pass

    return ''.join(new_word)

print(remove_vowels('perception'))

Answer 2

As mentioned in comments, working on the element you are iterating on, is often troublesome. How about this:

Code:

def remove_vowels(word):
    vowels = set('aeiou')
    return ''.join(l for l in word if l not in vowels)

Test Code:

print(remove_vowels('perception'))

Results:

prcptn

Answer 3

def remove_vowels(word):

    vowels = ['a', 'e', 'i', 'o', 'u']

    word = list(word)
    result = list()
    for letter in word:
        print('Looking for letter {}'.format(letter))

        if letter.lower() not in vowels:
            try: 
                result.append(letter)
            except ValueError:
                pass

    return ''.join(result)


print(remove_vowels('perception')) 

Answer 4

def remove_vowels(word):

vowels = ['a', 'e', 'i', 'o', 'u']

word = list(word)
word_new = []
for letter in word:
    print('Looking for letter {}'.format(letter))
    if letter.lower() in vowels:
        continue
    else:
        word_new.append(letter)

return ''.join(word_new)
print(remove_vowels('perception'))