SiaProgrammingPython

Interaction with the operating system

The modules sys and os provide the basic interface to the operating system. The module os creates a portable abstraction layer which is used by high-level modules like glob, socket, thred, time, fcntl.

Module sys

The module sys provides access to system-specific parameters by the interpreter.

Example argv

   1 #system1.py
   2 import sys
   3 print sys.argv

run system1.py parameter1 parameter2
['system1.py', 'parameter1', 'parameter2']

The script prints the command line arguments that are passed to the script. argv[0] is the script name

A more sophisticated way of evaluating command line arguments is provided by the module optparse

Module os

The module os is a portable operating system interface.

Some examples:

• os.system() Executes the command (a string) in a subshell

• os.mkdir() Creates a directory

• os.remove() Deletes a file

• os.path.isdir() Test if directory

• os.path.isfile() Test if file

• os.path.exists() Test if file or directory exists

• os.path.getsize() Size of a file

• os.path.basename() Base name of pathname

Module glob

The module glob finds all the pathnames matching a specified pattern according to the rules used by the Unix shell.

The following example looks for all pdf files in the current working directory and converts them into postscript files.

   1 #!/usr/bin/env python
   2 import os,glob
   3 
   4 filelist=glob.glob('*.pdf')
   5 for f in filelist:
   6     psfilename=f.split('.')[0]+'.ps'
   7     cmd='pdftops '+f+' '+psfilename
   8     print cmd
   9     os.system(cmd)

Unix Specific Services

Features that are unique to the Unix operating system are for example shell pipelines that pipe the output of one program to another. The pipeline symbol is |. For example, the command ls -s | sort -rg pipes the output of ls whit the option s (size) to the sort program. The result is a list of filenames sorted by its size