Python - String replace Example

Replace. A string cannot be changed in-place. We cannot assign characters. Instead we use the replace method to create a new string.

With this method, we specify a substring that we want to replace, and another we want to replace it with. We can use an optional second argument.

First example. Let us begin with this simple example. Replace accepts two substring arguments: the "before" and "after" parts that are replaced.

And The third argument is optional. It is a count. It indicates the maximum number of instances to replace.

Tip Replace only handles substrings, not characters. If you need to replace many single characters, please consider the translate method.

String translate

value = "aabc" # Replace a substring with another. result = value.replace("bc", "yz") print(result) # Replace the first occurrence with a substring. result = value.replace("a", "x", 1) print(result)

aayz xabc

Replace count. The third argument to replace() is optional. If we specify it, the replace method replaces that number of occurrences—this is a count argument.

Here We have a string that says "cat cat cat" and we replace all occurrences, 0 occurrences, and 1 and 2 occurrences.

before = "cat cat cat" print(before) # Replace all occurrences. after = before.replace("cat", "bird") print(after) # Replace zero occurrences. # ... This makes no sense. after = before.replace("cat", "bird", 0) print(after) # Replace 1 occurrence. after = before.replace("cat", "bird", 1) print(after) # Replace first 2 occurrences. after = before.replace("cat", "bird", 2) print(after)

cat cat cat bird bird bird cat cat cat bird cat cat bird bird cat

Regular expressions. Occasionally we need complex string replacement logic—for example, replacing substrings starting with certain letters. The re.sub method, part of the "re" module, works here.

re.sub

Here We replace all substrings in a string starting with the 3-letter sequence "car" and replacing the entire match with the word "bird."

import re # Replace all words starting with "car" with the string "bird". s = "carrots trees cars" v = re.sub(r"car\w*", "bird", s) print(v)

bird trees bird

A note. Replace() is needed to change a part of string to a new string. If the index of the match is known, we could use two slices and then construct a new string with concatenation.

Substring

Summary. With replace() we copy a string. The original is not changed. The copied string has the specified number of substrings replaced with a new substring (if found).

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This page was last updated on Sep 20, 2024 (new example).

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