How to Fix: TypeError: ‘str’ object does not support item assignment

This error means you tried to change a single character inside a string. If you see a TypeError str item assignment in Python, it’s an easy mistake to make, but it fails because strings are Immutable in Python.

The Cause

You can access characters by index, but you can’t assign a new character to an index.

Problem Code:

message = "Hello"
message[0] = "J" # Try to change 'H' to 'J'
# CRASH! TypeError: 'str' object does not support item assignment

The Fix: Create a New String

You cannot change the original string. You must build a new string that includes your change.

Fix 1: Using Slicing + Concatenation

message = "Hello"
new_message = "J" + message[1:] # 'J' + 'ello'

print(new_message) # Output: Jello

Fix 2: Using .replace()

If you want to replace all instances of a character, .replace() is easier.

message = "Hello"
new_message = message.replace("H", "J")

print(new_message) # Output: Jello

Just remember: message.replace() doesn’t change message; it returns a new string with the replacement made.