Replacing single character in string

Question

I have to create a code which will replace one character/letter from a string.

The example that I got was this:

string_substituting_char('abcdeeaa', 'c') 

Should return:

'ab$deeaa'

And I know which code to use so I used this code, but I only know the code to replace all the letter in string:

def string_substituting_char (st, ch):
    for ch in st:
        st = st.replace(ch, '$')
    return st

Code that I have and used (it replaces all the characters)

I want to know what should be added into the code so that it only changes one specific character from the string.

Answer 1

Simply return the result of the call to str.replace :

def string_substituting_char(st, ch):
    return st.replace(ch, '$')

Demo:

>>> def string_substituting_char(st, ch):
...     return st.replace(ch, '$')
...
>>> string_substituting_char('abcdeeaa', 'c')
'ab$deeaa'
>>>

Or, if you want to only replace the first occurrence of a character, you can pass 1 to the count parameter:

def string_substituting_char(st, ch):
    return st.replace(ch, '$', 1)

Demo:

>>> def string_substituting_char(st, ch):
...     return st.replace(ch, '$', 1)
...
>>> string_substituting_char('abcabc', 'c')
'ab$abc'
>>>

Answer 2

If you want to replace every instance of the given character use this:

>>> def string_substituting_char (st, ch):
...     return st.replace(ch, '$')
... 
>>> string_substituting_char('abccdefccsfdds', 'c')
'ab$$def$$sfdds'

Answer 3

Using regex

import re

def string_sub (str, ch):
    return "$".join(re.findall("[^" + ch + "]+", str))

---

Demo:

>>> string_sub("ello this is aea sa s as", "e")
'$llo this is a$a sa s as'