Python script to sorts the `names.txt` file containing lines like `Name Surname` alphabetically by Surname and write the result to the `names_sorted.txt` file.

nsort.py

#!/usr/bin/env python
# _*_ coding: utf-8 _*_

"""
This script sorts the `names.txt` file containing lines like `Name Surname` alphabetically by Surname
and writes result to the `names_sorted.txt` file.
"""
import sys


def main():
    """
    (Optional) arguments: input and output file name.
    """
    file_in = sys.argv[1] if len(sys.argv) > 1 else 'names.txt'
    file_out = sys.argv[2] if len(sys.argv) > 2 else 'names_sorted.txt'

    input_text = ""
    try:
        f = open(file_in, "r")
        input_text = f.read()
        f.close()
    except Exception as e:
        print(e)
        exit(0)

    print("UNSORTED: \n")
    print(input_text + "\n")

    unsorted_lines = input_text.splitlines()

    # Let's swap `Name Surname` to `Surname Name` order
    swapped = []
    for line in unsorted_lines:
        words = line.split()
        swap(words)
        swapped.append(" ".join(words))

    # sort by Surname
    sorted_lines = sorted(swapped)

    # Swap `Surname Name` back to `Name Surname`
    unswapped = []
    for line in sorted_lines:
        words = line.split()
        swap(words)
        unswapped.append(" ".join(words))

    print("SORTED: \n")
    output = '\n'.join(unswapped)
    print(output)

    f = open(file_out, "w")
    f.write(output)
    f.close()


def swap(m_list):
    tmp = m_list[0]
    m_list[0] = m_list[1]
    m_list[1] = tmp


if __name__ == "__main__":
    main()