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Python Python Collections (2016, retired 2019) Lists Disemvowel

akoniti
akoniti
1,410 Points
Posted by akoniti
akoniti
1,410 Points

Disemvowel - So close!

I'll be honest, and admit that I initially gave up on this challenge during the Lists block of Python Basic, and moved on to Slices. Now that I've finished that (and gained additional skills and knowledge), I'm back to my old nemesis :)

I've very close to solving it. My code works great in every instance except when two vowels in a row are present in the input. In that case, it faithfully deletes the first vowel, but keeps the second vowel in the list.

I've tried and tested so many different approaches, and gone through the logic on a whiteboard multiple times, and am at a loss. There must be some aspect of iterating through (and simultaneously modifying) a list that I'm overlooking which is the cause. My thought is that it has something to do with the 'index' variable, and how I'm increasing it as my for loop iterates, but I can't crack it.

Any input would be much appreciated!

disemvowel.py 
def disemvowel(word):
    index = 0
    vowels = ["a","e","i","o","u"]
    mod_list = list(word)
    for step in mod_list:
        if step.lower() in vowels: 
            del mod_list[index]
        index += 1 
    return ''.join(mod_list)
akoniti
akoniti
1,410 Points
akoniti
akoniti
1,410 Points

Yes! Thank you 🍹 Dave 🌴 StSomeWhere!

Your advice to 'Remember that word is a string, still iterable just immutable' was exactly what I needed. Simply iterating through word, and only moving the indexes that were not vowels into mod_list did the trick. The only hitch was that I was left with trailing indexes not overwritten, but a final del mod_list[index:] before the return clears that up. 

def disemvowel(word):
    index = 0
    vowels = ["a","e","i","o","u"]
    mod_list = list(word)
    for step in word:
        if step.lower() not in vowels: 
            mod_list[index] = step
            index += 1
    del mod_list[index:]
    return ''.join(mod_list)

EDIT

Thinking about it more, mod_list doesn't actually need to be created from word with this approach. I can just make it an empty list, and use .append to add index values to it, which means I can eliminate the del mod_list[index:] step:

def disemvowel(word):
    index = 0
    vowels = ["a","e","i","o","u"]
    mod_list = []
    for step in word:
        if step.lower() not in vowels: 
            mod_list.append(step)
            index += 1
    return ''.join(mod_list)
Dave StSomeWhere
Dave StSomeWhere
19,870 Points
Dave StSomeWhere
Dave StSomeWhere
19,870 Points

Glad you got it figured out. Just to point out that it can be simpler, you don't need the index stuff and could just use list.remove() like:

def disemvowel(word):
    vowels = ["a","e","i","o","u"]
    mod_list = list(word)
    for step in word:
        if step.lower() in vowels: 
            mod_list.remove(step)
    return ''.join(mod_list)
akoniti
akoniti
1,410 Points
akoniti
akoniti
1,410 Points

Ah! Yes, that approach is simpler. I think I've just been so fixated on fiddling with specific indexes on this one, for so long, that I'm blind to other approaches :) Thanks again for your quick help, your guidance was expert.

1 Answer

Dave StSomeWhere
Dave StSomeWhere
19,870 Points
Dave StSomeWhere
Dave StSomeWhere
19,870 Points

First, kudos for knowing what is wrong, that's the most important thing.

So, why do you want to iterate and simultaneously modify a list? In order to do that would involve some pain in the noodle index control.

Now, what other options do we have?

  1. You could always do a deep copy on the list and then iterate over the 1st list and modify the deep copy.
  2. You could also iterate over the original string which you called word and modify mod_list - this seems to me to be the easiest approach. Remember that word is a string, still iterable just immutable.