decompressing various archive types (See related posts)

#!/usr/bin/env python
#
# simple python script for extracting mostly used types of archives
# this script extracts .tar, .tar.gz, .tar.bz2, .gz and .zip archives 
#

import sys	# required for fetching command line arguments 
import os	# required for calling commands for archive extracting

def unpack(s):									# this is definition of depack
	if (s.find('.tar.gz') != -1):				#	function. It takes string
		os.system("tar -xvvzf " + filename)		#   filename as argument.
	elif (s.find('.tar.bz2') != -1):			#	functon than calls 
		os.system("tar -xvvjf " + filename)		#   appropriate command according
	elif (s.find('.tar') != -1):				# 	to file extension
		os.system("tar -xvvf " + filename)
	elif (s.find('.gz') != -1):
		os.system("gunzip" + filename)			
	elif (s.find('.zip') != -1):		
		os.system("unzip " + filename)
	else: print "Wrong archive or filename"		# other types not supported

try:											# this is main program
	filename = sys.argv[1]						# first argument right after
	unpack(filename)							#	'unpack' command goes in the
except IndexError:								#	filename string
	print "Filename is invalid!"				#	than the depack function is called

# try-except block is used for handling IndexError exception if no argument is passed