Python String replace() Method

The replace() method in Python is used to replace parts of a string with another string. It’s a very useful and beginner-friendly tool for text processing.

Syntax

string.replace(old, new, count)

Parameters:

• old – The substring you want to replace.
• new – The substring you want to replace it with.
• count (optional) – The number of times you want to replace old with new. If omitted, all occurrences are replaced.

Returns:

• A new string with replacements applied. The original string is not modified.

Example 1: Basic Replacement

text = "I love apples"
new_text = text.replace("apples", "bananas")
print(new_text)

I love bananas

Example 2: Replace All Occurrences

quote = "ha ha ha!"
print(quote.replace("ha", "ho"))

ho ho ho!

Example 3: Replace Only First Occurrence

data = "one one one"
print(data.replace("one", "two", 1))

two one one

Use Cases of replace()

• Correcting typos in strings
• Formatting text
• Removing unwanted characters (e.g., replace(",", "") to remove commas)
• Replacing sensitive or restricted words

Common Mistakes

• Strings are immutable: replace() returns a new string – it does not change the original.
• Trying to replace a substring that doesn't exist has no effect (no error).
• Remember that it's case-sensitive: "hello".replace("H", "J") does nothing.

Interview Tip

Use replace() when cleaning strings or doing simple data transformations. It’s often seen in string manipulation questions or during preprocessing.

Summary

• replace() is used to replace parts of a string with a new value.
• You can specify how many times to replace with the optional count parameter.
• Returns a new string; the original remains unchanged.

Practice Problem

Write a program to replace all spaces in a sentence with dashes -.

sentence = input("Enter a sentence: ")
print(sentence.replace(" ", "-"))