replace string in existing file python code example

Example 1: python replace text in file

filename = "sample1.txt"
# SAMPLE1.TXT
# Hello World!
# I am a human.

with open(filename, 'r+') as f:
    text = f.read()
    text = re.sub('human', 'cat', text)
    f.seek(0)
    f.write(text)
    f.truncate()

# SAMPLE1.TXT
# Hello World!
# I am a cat.

Example 2: change part of a text file python

#!/usr/bin/env python3
import fileinput

with fileinput.FileInput(filename, inplace=True, backup='.bak') as file:
    for line in file:
        print(line.replace(text_to_search, replacement_text), end='')