Concise Python Tutorials

Brief introduction

The Python standard library is installed with Python and contains a large number of extremely useful modules. It is important to familiarize yourself with the Python standard library, because if you are familiar with the modules in these libraries, most of your problems can be solved using them quickly and easily.

We have studied some of the common modules in this library. You can learn the full content of all the modules in the Python standard library in the "Library references" section of the documentation that is included with the Python installation.

SYS module

The SYS module contains the functions that the system corresponds to. We've learned the SYS.ARGV list, which contains command-line arguments.

Command line arguments

Example 14.1 using SYS.ARGV

#!/usr/bin/python
# Filename: cat.py
import sys
def readfile(filename):
'''Print a file to the standard output.'''
f = file(filename)
while True:
line = f.readline()
if len(line) == 0:
break
print line, # notice comma
f.close()
# Script starts from here
if len(sys.argv) < 2:
print 'No action specified.'
sys.exit()
if sys.argv[1].startswith('--'):
option = sys.argv[1][2:]
# fetch sys.argv[1] but without the first two characters
if option == 'version':
print 'Version 1.2'
elif option == 'help':
print '''\
This program prints files to the standard output.
Any number of files can be specified.
Options include:
--version : Prints the version number
--help　　: Display this help'''
else:
print 'Unknown option.'
sys.exit()
else:
for filename in sys.argv[1:]:
readfile(filename)