Python string.replace() – How to Replace a Character in a String

Python has numerous string modifying methods, and one of them is the replace method.

In this article, I'll show you how this method can be used to replace a character in a string.

How the replace Method Works in Python

The replace string method returns a new string with some characters from the original string replaced with new ones. The original string is not affected or modified.

The syntax of the replace method is:

string.replace(old_char, new_char, count)

The old_char argument is the set of characters to be replaced.

The new_char argument is the set of characters that replaces the old_char.

The count argument, which is optional, specifies how many occurrences will be replaced. If this is not specified, all occurrences of the old_char will be replaced with the new_char.

Let's see some examples.

string.replace() Examples

Here's an example that replaces "JavaScript" with "PHP" in a string:

str = "I love JavaScript. I prefer JavaScript to Python because JavaScript looks more beautiful"

new_str = str.replace("JavaScript", "PHP")

print(new_str)
# I love PHP. I prefer PHP to Python because PHP looks more beautiful

You can see how the replace method replaces the "JavaScript" occurences with "PHP".

In this example, the three occurrences of "JavaScript" are replaced with "PHP". What if you wanted only one occurrence to be replaced? Then you can use the count argument like this:

str = "I love JavaScript. I prefer JavaScript to Python because JavaScript looks more beautiful"

new_str = str.replace("JavaScript", "PHP", 1)

print(new_str)
# I love PHP. I prefer JavaScript to Python because JavaScript looks more beautiful

By applying a count argument of 1, you can see that only the first "JavaScript" (the first occurrence) is replaced with "PHP". The remaining "JavaScript"s stays untouched.

When to Use the replace Method in Python

A good use case of this method is to replace characters in a user's input to fit some standard.

Let's say, for example, you want users to enter their usernames but you don't want the whitespace character in the username input. You can use the replace method to replace the whitespaces in the submitted strings with a hyphen. Here's how to do that:

user_input = "python my favorite"

updated_username = user_input.replace(" ", "-")

print(updated_username)
# python-my-favorite

From the result of the replace method, you can see that the whitespaces have been replaced with hyphens which meets your standard.

Wrapping Up

The replace method replaces an existing substring in a string with a new substring. You specify how many occurrences of the existing substring are to be replaced with the count argument of the method.