Question

Programming Exercise 4.9

Write a script named numberlines.py. This script creates a program listing from a source program.

This script should:

Prompt the user for the names of two files.

The input filename could be the name of the script itself, but be careful to use a different output filename!

The script copies the lines of text from the input file to the output file, numbering each line as it goes.

The line numbers should be right-justified in 4 columns, so that the format of a line in the output file looks like this example:

   1> This is the first line of text. 

Programming Exercise 4.9 Instructions Write a script named numberlines.py. This script creates a program listing from a source program This script should: 1. Prompt the user for the names of two files. o The input filename could be the name of the script itself, but be careful to use a different output filename! 2. The script copies the lines of text from the input file to the output file, numbering each line as it goes. 3. The line numbers should be right-justified in 4 columns, so that the format of a line in the output file looks like this example: 1> This is the first line of text.

Answer 1

input_filename = input('Enter input file name: ')
output_filename = input('Enter output file name: ')

with open(input_filename, 'r') as f, open(output_filename, 'w') as w:
    number = 0
    for line in f:
        number += 1
        w.write('{:>4}> {}'.format(number, line))