find a substring in a file python code example

Example 1: how to check if a string is in a file python

def search_string_in_file(file_name, string_to_search):
    """Search for the given string in file and return lines containing that string,
    along with line numbers"""
    line_number = 0
    list_of_results = []
    # Open the file in read only mode
    with open(file_name, 'r') as read_obj:
        # Read all lines in the file one by one
        for line in read_obj:
            # For each line, check if line contains the string
            line_number += 1
            if string_to_search in line:
                # If yes, then add the line number & line as a tuple in the list
                list_of_results.append((line_number, line.rstrip()))
 
    # Return list of tuples containing line numbers and lines where string is found
    return list_of_results

Example 2: python read text file look for string

f = open(filename,  "r")
   whattoReturn = "None"
   if strToFind in f.read():
      whattoReturn = strToFind