Programming Python, 3rd Edition

Packing and Unpacking Files

Many moons ago (about 10 years), I used machines that had no tools for bundling files into a single package for easy transport. Here is the situation: you have a large set of text files laying 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. As mentioned in an earlier footnote, even Python itself has grown to support zip and tar archives in the standard library (see the zipfile and tarfile modules in the library reference).

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

Example 6-6. PP3E\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 3. If we give textpack.py ...