Python string.replace() not replacing certain characters

Question

def replace_at_index(string, index):
    print (string.replace(string[index], "-", 1))

That's my current code for replacing a character with a given index.

string "House" with Index 4 produces "Hous-"
string "Housee" with Index 5 produces "Hous-e"
string "Houseed" with Index 6 produces "Housee-"
string "Houseed" with Index 5 produces "Hous-ed"

Not sure why it's doing this. The result I'm wanting is for it to replace the given Index, which in the case of "Housee" Index 5 would be "House-"

It's replacing the first occurrence of the character you asked it to replace. If there are duplicate characters, it won't necessarily be at the same index that you got the character from. — Barmar, Mar 11 '21 at 19:49

score 3 · Answer 1 · edited Mar 11 '21 at 19:57

3

This is a hack but works:

def replace_at_index(string, index):
   ls = list(string)
   ls[index] = "-"
   s = "".join(ls)
   print(s)

edited Mar 11 '21 at 19:57

wjandrea

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answered Mar 11 '21 at 19:53

ESDAIRIM

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1

That's not a hack at all, that's a perfectly fine implementation. – wjandrea Mar 11 '21 at 19:57

score 2 · Accepted Answer · answered Mar 11 '21 at 19:54

Look at the function doc-string: string.replace(old, new, count) so it replaces count as many occurences that it can find.

You cannot change a string. Each string is newly created, it is immutable. What you want is:

def replace_at_index(string, index):
    string = string[:index] + "-" + string[index+1:]
    return string

Hiram · Answer 3 · 2021-03-11T20:11:49.833

1

The replace method replaces a given substring in a string.

What the code is doing, it's replacing the first occurrence of the character in the string.

What you should do instead is:

def replace_at_index(string, index):
    new_string = string[:index]
    new_string += "-"
    new_string += string[index+1:]
    return new_string

In a pythonic fashion ;)

edited Mar 11 '21 at 20:11

answered Mar 11 '21 at 19:50

Hiram

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Strings are immutable. – Barmar Mar 11 '21 at 19:50
Yep. Long time programming in C led to this – Hiram Mar 11 '21 at 19:53
1

Using `+=` on strings is actually [not super Pythonic](https://stackoverflow.com/a/39680089/4518341), but either way, it's simpler to join all at once: `new_string = string[:index] + '-' + string[index+1:]` – wjandrea Mar 11 '21 at 20:05
By pythonic i meant by using string slices. Thanks for the observation, though :) – Hiram Mar 11 '21 at 20:12

trozzel · Answer 4 · 2021-03-11T19:57:27.320

1

str.replace is not replacing the index, but the first occurrence of a value. Since "Housee"[5] == 'e', it will replace the first 'e'

def replace_at_index(string, index):
    newstr = string[:index] + '-' + string[index+1:]
    return newstr

edited Mar 11 '21 at 19:57

answered Mar 11 '21 at 19:50

trozzel

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wjandrea · Answer 5 · 2021-03-11T20:11:05.077

It's replacing the first occurrence of the character you asked it to replace. If there are duplicate characters, it won't necessarily be at the same index that you got the character from.

-- comment by Barmar

What you could do instead is slice the string at the index, then join it on the replacement.

def replace_at_index(string, index):
    parts = string[:index], string[index+1:]
    return "-".join(parts)


for s, i in ("House", 4), ("Housee", 5), ("Houseed", 6), ("Housee", 5):
    print(replace_at_index(s, i))

Output:

Hous-
House-
Housee-
House-

Although you might want to add a check to make sure that index is in range.

score 0 · Answer 6 · edited Jul 05 '22 at 17:36

0

its replacing you just have to be a little smart about it:

b = '?<\>:/"|'
line='?sqfsq?QSqdqdf/qsdfqsdf\qsdfqs"'
s=""
for char in b:
    print(char)
    # if char in b:
    s=(line.replace(char,''))
    line=s
print(line)
print(s)

edited Jul 05 '22 at 17:36

kilojoules

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answered Jul 04 '22 at 15:20

Pedro oumari

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Python string.replace() not replacing certain characters

6 Answers6