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Python Program to Replace a Character in a String

Beginner · Strings

This program replaces every copy of one character in a string with another, so "banana" with a replaced by o becomes "bonono". Strings cannot be changed in place, so the result is a new string.

Program

replace_character.py
text = "banana" # or: text = input("Enter a string: ")
old = "a" # or: old = input("Character to replace: ")
new = "o" # or: new = input("Replace it with: ")
result = text.replace(old, new)
print("Original string:", text)
print(f"After replacing '{old}' with '{new}':", result)
Output
Original string: banana
After replacing 'a' with 'o': bonono

How it works

  1. text.replace(old, new) returns a new string in which every old is changed to new.
  2. The original text is not modified, because strings in Python are immutable.
  3. replace() is case-sensitive, so replacing "a" leaves any "A" alone.
  4. replace() also works on longer pieces of text, like replace("cat", "dog").

Other ways to write it

Without replace()

Without replace()
text = "banana"
old, new = "a", "o"
result = ""
for ch in text:
if ch == old:
result += new
else:
result += ch
print(text, "->", result)
Output
banana -> bonono

The loop copies the string one character at a time and puts in new whenever it meets old.

Replace only the first one, or one position

Replace only the first one, or one position
text = "banana"
print("First 'a' only:", text.replace("a", "o", 1))
# Strings cannot be changed by index, so rebuild the string around position 2
pos = 2
print("Position 2 changed:", text[:pos] + "N" + text[pos + 1:])
Output
First 'a' only: bonana
Position 2 changed: baNana

The third argument of replace() limits how many replacements are made. text[2] = "N" would raise a TypeError, so slicing builds the new string instead.

Try it yourself

Replace every space in "I love Python" with an underscore.

Edit the program above and press Run, or open it in the full editor to save it and share it. To watch it run line by line, open it in the visualizer.

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