CODEWITHSUNDEEP
pythonloopsfor-loop
Igor Skoldin
Igor Skoldin

Reputation: 750

Python for loop is not looping through all items

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?

Upvotes: 3

Views: 12320

Answers (4)

Devendra Lattu
Devendra Lattu

Reputation: 2812

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'))

Upvotes: 0

R.A.Munna
R.A.Munna

Reputation: 1709

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'))

Upvotes: 0

Mike Tung
Mike Tung

Reputation: 4821

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'))

Upvotes: 7

Stephen Rauch
Stephen Rauch

Reputation: 49812

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

Upvotes: 1

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