Python - replace first n characters in string

In this article, we would like to show you how to replace first n characters in string in Python.

Quick solution:

text = "ABCD ABCD ABCD"
n = 3
replacement = "XYZ"
result = text.replace(text[0:n], replacement, 1)

print(result)  # XYZD ABCD ABCD

Practical example using replace() method

In this example, we use replace() method to replace first n characters in the text string.

We use the following syntax:

replace(old, new, count)

Where:

• old - is a substring to replace,
• new - is the replacement,
• count (optional argument) - is the number of times we want to replace the specified substring. You need to set it to 1, so you won't replace anything but the first occurrence of the substring.

Practical example:

text = "ABCD ABCD ABCD"
n = 3
replacement = "XYZ"
result = text.replace(text[0:n], replacement, 1)

print("Before: ", text)    # ABCD ABCD ABCD
print("After:  ", result)  # XYZD ABCD ABCD

Output:

Before:  ABCD ABCD ABCD
After:   XYZD ABCD ABCD

Note:

If you don't set the count argument, by default the replace() method will replace all occurrences of the ABC substring.

Output:

Before:  ABCD ABCD ABCD
After:   XYZD XYZD XYZD

References

• Python 3.x documentation - String replace() method