Change an element of an array using a for loop in Python

Question

I'm trying to teach myself Python and am doing some menial tasks with it. At the minute I'm working with lists and strings. I know that strings are immutable so I'm converting a string to a list and want to loop over the list to change any vowels to $ signs. The problem is that the $ sign isn't being attributed to the vowels. Here is my code:

aString = raw_input("Please enter a sentence: ")

aString = list(aString)

for i in xrange(len(aString)):
    if i=='a' or \
       i=='e' or \
       i=='i' or \
       i=='o' or \
       i=='u':
        i.newattribute = '$'

print aString

@MaksymPolshcha Thanks for that. Have to do a bit more research into loops etc in Python. There's a lot to them — adohertyd
– adohertyd, Commented May 11, 2012 at 16:20

Elias Dorneles · Accepted Answer · 2012-05-11 16:24:04Z

4

I know you are doing it to learn the language, but you should know you could simply use the method sub to substitute with a regular expression:

import re
re.sub('[aeiou]', '$', aString)

answered May 11, 2012 at 16:24

Elias Dorneles

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Comments

Niek de Klein · Accepted Answer · 2012-05-11 16:20:09Z

2

You want to do the following:

for i in xrange(len(aString)):
    if aString[i]=='a' or \
       aString[i]=='e' or \
       aString[i]=='i' or \
       aString[i]=='o' or \
       aString[i]=='u':
          aString[i] = '$'

But it would probably be easier to use the replace method.

replaceList = ['a', 'e', 'i', 'o', 'u']
aString = raw_input("Please enter a sentence: ")
for letter in replaceList:
    aString.replace(letter)
print aString

edited May 11, 2012 at 16:20

answered May 11, 2012 at 16:14

Niek de Klein

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1 Comment

adohertyd Over a year ago

The replace function is something that I haven't seen before. Thanks for that Niek. Python is full of these new functions that I haven't seen before. I'm only familiar with C and C++

Ashwini Chaudhary · Accepted Answer · 2012-05-11 16:32:27Z

2

strs="abcduitryd"
print("".join(('$' if x in 'aeiou' else x for x in strs)))

$bcd$$tryd

or:

strs="abcduitryd"
lis=list(strs)
for i,x in enumerate(lis):
    if x in 'aeiou':
        lis[i]='$'
strs="".join(lis)
print(strs)

$bcd$$tryd

or :

strs="abcduitryd"
for i,x in enumerate(strs):
    if x in 'aeiou':
        strs=strs.replace(strs[i],'$')
print(strs)

$bcd$$tryd

edited May 11, 2012 at 16:32

answered May 11, 2012 at 16:20

Ashwini Chaudhary

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2 Comments

ch3ka Over a year ago

you don't have to list() the string. a string is an iterable.

Ashwini Chaudhary Over a year ago

oh! i forgot to remove that line, when I copied this from the IDE.

asafm · Accepted Answer · 2012-05-11 16:42:29Z

1

The "Pythonic" way is to use the translate method for string.
example:

import string
mystr="hello world"
vowels="aeiou"
token="$"*len(vowels)
tab=string.maketrans(vowels,token)
mystr.translate(tab)
'h$ll$ w$rld'

answered May 11, 2012 at 16:42

asafm

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Comments

user1342784 · Accepted Answer · 2012-05-11 16:43:24Z

1

If you are learning python, one cool feature that can be used is a list comprehension. You can do this:

>>> str = "hello world"
>>> l = ["$" if ch in "aeiou" else ch for ch in str]
>>> str = "".join(l)
>>> str
'h$ll$ w$rld'

The second line builds a list, walking through each character and applying `"$" if ch in "aeiou" else ch1 to it. You then just join the list to get a new string. It's doing exactly what you are trying to do, converting the string to a list and in the process, coverting vowels to '$'.

This is not the most efficient way to do it of course. The best way to do it is to use a library meant for this sort of thing as others have mentioned.

answered May 11, 2012 at 16:43

user1342784

1 Comment

kindall Over a year ago

You don't really need to make a separate list, you can just change that to a generator expression and put it right inside "".join().

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