TypeError 'str' object does not support item assignment

The Problem

When you run the code below, Python will throw the runtime exception TypeError: 'str' object does not support item assignment.

text = "hello world"
if text[0].islower():
    text[0] = text[0].upper()

This happens because in Python strings are immutable, and can’t be changed in place.

The Solution

The solution is to use one of Python’s built in functions for string manipulation. In this particular case, capitalize() is what you’ll need.

text = "hello world"
text = text.capitalize()

Note that capitalize creates a new string and returns that new string. That’s why we have to assign that new string to the text variable. In the example below, text would remain unchanged, and capital would have the result of capitalizing the text variable.

text = "hello world"
capital = text.capitalize()

Further Reading

If you’re looking to get a deeper understanding of how Python application monitoring works, take a look at the following articles:


Evan Hicks

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