Adding line numbers to the output in Python

Question

For example, if the input file is:

def main():
    for i in range(10):
        print("I love Python")
    print("Good bye!")

Answer 1

Use a with statement to close the file buffer and just concatenate strings:

with open('file.txt', 'r') as program:
    data = program.readlines()

with open('file.txt', 'w') as program:
    for (number, line) in enumerate(data):
        program.write('%d  %s' % (number + 1, line))