Programming Python, Second Edition

Packing and Unpacking Files

Many moons ago (about five years), I used machines that had no tools for bundling files into a single package for easy transport. The situation is this: you have a large set of text files lying around that you need to transfer to another computer. These days, tools like tar are widely available for packaging many files into a single file that can be copied, uploaded, mailed, or otherwise transferred in a single step. Even Python itself has grown to support zip archives in the 2.0 standard library (see module zipfile).

Before I managed to install such tools on my PC, though, portable Python scripts served just as well. Example 4-6 copies all the files listed on the command line to the standard output stream, separated by marker lines.

Example 4-6. PP2E\System\App\Clients\textpack.py

#!/usr/local/bin/python
import sys                           # load the system module
marker = ':'*10 + 'textpak=>'     # hopefully unique separator

def pack(  ):
    for name in sys.argv[1:]:        # for all command-line arguments
        input = open(name, 'r')      # open the next input file
        print marker + name          # write a separator line
        print input.read(  ),        # and write the file's contents

if __name__ == '__main__': pack(  )  # pack files listed on cmdline

The first line in this file is a Python comment (#...), but it also gives the path to the Python interpreter using the Unix executable-script trick discussed in Chapter 2. If we give textpack.py executable permission with a Unix chmod command, we can pack files by running this ...