Filtering objects from lists in python

Question

I'm trying to program something that will filter all the vowels out of a string of text and I'm not sure why my function doesn't work. Here's my code

def anti_vowel(text):
 letters = text.split() #make a list of all the letters in the string
 index = 0 #for del
 for x in letters:
     if x == "a" or x == "A" or x == "u" or x == "U" or x == "i" or x == "I" or x == "o" or x == "O" or x == "e" or x == "E":
         del letters[index]
     index += 1 #to make the if-clause work
 return "".join(letters) #turn the edited list into a string

While iterating over letters the if-clause should be activated when the object in letters is a vowel right? so it should delete that object. But what am I doing wrong?

You are using del letters[index]. The list is getting smaller and smaller, and when you do index += 1 you are actually skipping over an element(which was moved because of the delete). — Kamehameha
– Kamehameha, Commented Jul 14, 2015 at 17:17

Avinash Raj · Accepted Answer · 2015-07-14 17:26:27Z

5

I would use re.sub

re.sub(r'(?i)[AEIOU]', '', st)

Explanation:

(?i) case-insensitive modifier helps to do case insensitive match.
[AEIOU] matches any one charcater from the given list. Since we already added the case-insensitive modifier, this would match both upper and lowercase vowels.

edited Jul 14, 2015 at 17:26

answered Jul 14, 2015 at 17:15

Avinash Raj

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1 Comment

Bhargav Rao Over a year ago

Mind adding a link to re.sub there?

TigerhawkT3 · Accepted Answer · 2015-07-14 17:18:47Z

4

Your code isn't iterating through letters, it's iterating through words. This is because text.split() splits your text into a list of whitespace-separated "word" strings.

The next problem is that you're iterating through a list and deleting entries. Mutating an iterable while iterating through it is a common cause of strange results.

Instead, do something like this:

def anti_vowel(text):
    return ''.join(filter(lambda x: x.lower() not in 'aeioe', text))

Result:

>>> anti_vowel('hi my name is joe')
'h my nm s j'

answered Jul 14, 2015 at 17:18

TigerhawkT3

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Comments

Nir Alfasi · Accepted Answer · 2015-07-14 17:49:54Z

2

I rather Avinash's approach, but if you want to fix your impl. here's how to do it:

def anti_vowel(text):
    letters = list(text)
    i = 0
    while i < len(letters):
        x = letters[i]
        if x in "aAeEiIoOuU":
            del letters[i]
        else:
            i += 1
    return "".join(letters)

edited Jul 14, 2015 at 17:49

answered Jul 14, 2015 at 17:19

Nir Alfasi

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3 Comments

martineau Over a year ago

This doesn't work because the letters = text.split() splits the text into words that were separated by whitespace, not letters. Also, modifying what you're iterating over is generally a bad idea.

TigerhawkT3 Over a year ago

Keeping text.split(), this will only work if the string contains whitespace between each character.

martineau Over a year ago

if x in "aAeEiIoOuU": would be more succinct.

iobender · Accepted Answer · 2015-07-14 17:18:35Z

1

''.join(c for c in text if c.lower() not in 'aeiou')

This uses a generator expression to look at each letter in the string, and only keep it if it is not a vowel (its lowercase is not in 'aeiou'), then joins these valid characters.

answered Jul 14, 2015 at 17:18

iobender

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Comments

DJanssens · Accepted Answer · 2015-07-14 18:28:15Z

1

You could use list comprehension and create something like this

def anti_vowel2(text):
    return "".join([x for x in text if x.lower() not in 'aeiou'])

print(anti_vowel2("test"))

which outputs the string tst

edited Jul 14, 2015 at 18:28

answered Jul 14, 2015 at 17:22

DJanssens

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1 Comment

TigerhawkT3 Over a year ago

You can refactor that long predicate into simply if x.lower() not in 'aeiou'.

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