Anti_vowel function does not remove a vowel

Question

def anti_vowel(text):
    upper_vowels = ['A', 'E', 'I', 'O', 'U']
    lower_vowels = ['a', 'e', 'i', 'o', 'u']
    char_list = list(text)
    for char in char_list:
        if char in upper_vowels or char in lower_vowels:
            char_list.remove(char)
    new_word = ''
    for char in char_list:
        new_word += char
    return new_word

If I pass anti_vowel("Hey look Words!"), I get the result 'Hy lk Words!'. The 'o' in 'Words!' is not removed.

You might take a look on a [similar question](http://stackoverflow.com/questions/3939361/remove-specific-characters-from-a-string-in-python). — albert, Jun 26 '15 at 06:21
As you iterate through, you skip over the second o on the next iteration after you remove the first. Then on your next call to `char_list.remove(char)` you're actually removing the second `o` and not the 3rd. — Paul Rooney, Jun 26 '15 at 06:25
`return ''.join(c for c in text if c.lower() not in {'a', 'e', 'i', 'o', 'u'})` — Peter Wood, Jun 26 '15 at 06:35
@InvizTJ - You can accomplish this task in a much simpler way with a regular expression. Replace the entire body of your `anti_vowel(text)` function with this one line: `return re.sub( r'[aeiou]', '', text, 0, re.IGNORECASE )` — Michael Geary, Jun 26 '15 at 06:39
Yes, that approach is present [here](http://stackoverflow.com/questions/21581824/correct-code-to-remove-the-vowels-from-a-string-in-python) and [here](http://stackoverflow.com/questions/7301292/string-replace-vowels-in-python). — TigerhawkT3, Jun 26 '15 at 06:40
@TigerhawkT3 - Ah, thanks. In fact, the function name and test string are identical in one of those too. I should have known it's a homework question! — Michael Geary, Jun 26 '15 at 06:44

nneonneo · Answer 1 · 2015-06-26T06:30:34.810

3

As others have noted, you're modifying the list while you iterate over it. That's not going to work: the list changes size while you iterate, causing you to skip over some characters. You could use a list copy to avoid this, but maybe consider just using a better approach.

You can build the string up character-by-character, instead:

def anti_vowel(text):
    vowels = 'AEIOUaeiou'
    result = []
    for c in text:
        if c not in vowels:
            result.append(c)
    return ''.join(result)

This is faster, safer, shorter and easier to read than the original approach.

Alternately, you can use Python's powerful built-in string functions to do this very simply:

def anti_vowel(text):
    return text.translate(dict.fromkeys(map(ord, 'aeiouAEIOU')))

This pushes the text through a translation table that deletes all the vowels. Easy!

edited Jun 26 '15 at 06:30

answered Jun 26 '15 at 06:26

nneonneo

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Not as efficient, but for fun, another one liner option using list comprehension `word ="".join([x for x in text.lower() if x not in 'aeiou'])` – user3636636 Jun 26 '15 at 06:30
1

@user3636636: nice, though you probably want `in text if x.lower() not in 'aeiou'` to avoid accidentally lower-casing all the input. – nneonneo Jun 26 '15 at 06:31
good point, thanks will update! – user3636636 Jun 26 '15 at 06:36

score 0 · Answer 2 · 2015-06-26T06:27:54.793

Few things going on here.

Never modify lists while iterating through them. Your could create a simple copy by calling list[:] instead if you'd to continue using your technique.
Use list comprehension to simplify your code further.

Simplifying the code a bit:

def anti_vowel(text):
    upper_vowels = ['A', 'E', 'I', 'O', 'U']
    lower_vowels = [s.lower() for s in upper_vowels]
    char_list = list(text)
    for char in char_list[:]:
        if char in upper_vowels or char in lower_vowels:
            char_list.remove(char)
    return ''.join(char_list)

If you want to simplify everything under a single lambda then use the following:

anti_vowel = lambda text: ''.join([s for s in text if s.upper() not in ['A', 'E', 'I', 'O', 'U']])

You can call it like regular function anti_vowel(). The idea behind it as follows:

Iterate through every character, taking the upper case
Use list comprehension to create a new list out of those characters, only if they do not exist in the vowels. ([x for x in list])
Finally put the characters together (''.join([])

Anti_vowel function does not remove a vowel

2 Answers2