The following sections provide some examples that demonstrate several of the features of the os module.

import os

def get_directory_info(dir):
    os.chdir(dir)
    current_dir = os.getcwd()
    dir_contents = os.listdir(dir)
    print ""
    print "Current directory = ", current_dir
    print "Directory contents = ", dir_contents
    print""

get_directory_info('C:\python25')
get_directory_info('C:')

Current directory =  C:python25
Directory contents =  ['DLLs', 'Doc', 'include', 'Lib', 'libs', 'python.exe',
'python25.exe', 'pythonw.exe', 'pythonw25.exe', 'tcl', 'Tools', 'w9xpopen.exe']


Current directory =  C:
Directory contents =  ['$Recycle.Bin', 'autoexec.bat', 'Boot', 'bootmgr',
'BOOTSECT.BAK', 'config.sys', 'Documents and Settings', 'EasyEclipse-for-Python-
1.2.2.2', 'hiberfil.sys', 'jim', 'MSOCache', 'pagefile.sys', 'Program Files',
'ProgramData', 'Python25', 'ruby', 'sqmdata00.sqm', 'sqmnoopt00.sqm', 'System
Volume Information', 'Users', 'Windows']

import os

x = os.urandom(25)
y = x
z = os.urandom(25)

print "Does x = y? ", x==y
print "Does x == z? ", x==z
print "x = ", x

Does x = y?  True
Does x == z?  False
x = 12

The following examples show the time module in action.

import time

raw_input("Press the [Enter] key: ")
time1 = time.time()
raw_input("Wait a few seconds, then press the [Enter] key again: ")
time2 = time.time()
difference = int(time2 - time1)

print "There were ",  difference, "seconds bettween the two choices"

Press the [Enter] key:
Wait a few seconds, then press the [Enter] key again:
There were  5 seconds bettween the two choices

import time

print "GMT Time as tuple: ", time.gmtime()
print "GMT Time as string: ", time.asctime(time.gmtime())
print "Local Time as tuple: ", time.localtime()
print "Local time as string: ", time.asctime(time.localtime())
print "Formatted local time in <month day, year> format: ", 
      time.strftime("%B %d, %Y")

GMT Time as tuple:   (2008, 2, 11, 1, 10, 36, 0, 42, 0)
GMT Time as string:  Mon Feb 11 01:10:36 2008
Local Time as tuple:   (2008, 2, 10, 17, 10, 36, 6, 41, 0)
Local time as string:   Sun Feb 10 17:10:36 2008
Formatted local time in <month day, year> format:  February 10, 2008

The following example shows how the optparse module can create options for the user:

from optparse import OptionParser

parser = OptionParser()
parser.add_option("-n", "--name", dest="name",
                  help="print name")

(options, args) = parser.parse_args()

print "your name is ", options.name

If the user runs the program with the preceding command-line option, the following output results:

I:Applied_PythonChapter_9>python optparse-example1.py --name "Jim Knowlton"
your name is  Jim Knowlton

If the program is run with a --h option, then this is the output:

I:Applied_PythonChapter_9>python optparse-example1.py --h
Usage: optparse-example1.py [options]

Options:
  -h, --help            show this help message and exit
  -n NAME, --name=NAME  print name

The following example demonstrates how to query for a particular operating system and then branch the code based on the operating system in which the script is running:

import platform

if platform.system() == 'Windows':
    print "The platform is Windows"
    #put Windows-specific code here
elif platform.system() == 'Linux":
    print "The platform is Linux"
    #put Linux-specific code here

If the script is run on a Windows box, then it will return the following message:

The platform is Windows

If the script is run on a Linux box, then it will return this message:

The platform is Linux

The following example prompts for a password and if the correct password is entered, displays the login of the currently logged-in user:

import getpass

password = getpass.getpass()

if password == "letmein":
    print("Logged in username is " + getpass.getuser())

The following example queries a particular key in the Registry and outputs all the subkeys for that key:

import _winreg

explorer = _winreg.OpenKey(
    _winreg.HKEY_CURRENT_USER,
    "Software\Microsoft\Windows\CurrentVersion\Explorer")

# list values owned by this registry key
i = 0
try:
    while 1:
        name, value, type = _winreg.EnumValue(explorer, i)
        print repr(name),
        i += 1
except:
    print

The following is the output for this program:

I:Applied_PythonChapter_9>python winreg-example1.py
'ShellState' 'CleanShutdown' 'Browse For Folder Width' 'Browse For Folder Height
' 'link' 'Logon User Name'

The following example shows how to play various sounds with the winsound module:

import winsound

print "Play Windows exit sound."
winsound.PlaySound("SystemExit", winsound.SND_ALIAS)

print "Probably play Windows default sound"
winsound.PlaySound("*", winsound.SND_ALIAS)

print "Play a message beep"
winsound.MessageBeep()

print "Play an evil laugh"
winsound.PlaySound('evil_laugh.wav',winsound.SND_FILENAME)

As shown in the preceding example, the PlaySound() function has two parameters. The first parameter contains either audio data formatted as a string, a WAV file, or nothing. Its second parameter is a constant that tells the function what to do. The following table describes the available constants.

The MessageBeep() function takes an optional parameter of audio data formatted as a string. If no parameter is given (as in the preceding example), the MB_OK sound is played.

The following example shows how to start a service, stop a service, restart a service, or get service status through Python:

import win32serviceutil, time

def service_info(action, machine, service):
    if action == 'stop':
        win32serviceutil.StopService(service, machine)
        print '%s stopped successfully' % service
        time.sleep(3)
    elif action == 'start':
        win32serviceutil.StartService(service, machine)
        print '%s started successfully' % service
        time.sleep(3)
    elif action == 'restart':
        win32serviceutil.RestartService(service, machine)
        print '%s restarted successfully' % service
        time.sleep(3)
    elif action == 'status':
        if win32serviceutil.QueryServiceStatus(service, machine)[1] == 4:
            print "%s is running normally" % service
        else:
            print "%s is *not* running" % service

machine = 'localhost'
service = 'RemoteRegistry'

service_info('start', machine, service)
service_info('stop', machine, service)
service_info('start', machine, service)
service_info('restart', machine, service)
service_info('status', machine, service)

Because this example is a little longer than the others, let's examine it section by section.

The service_info function takes an action, a machine, and a service name as parameters:

def service_info(action, machine, service):

The rest of the function is simply an if structure that performs actions on the service based on the action parameter passed in:

if action == 'stop':
        win32serviceutil.StopService(service, machine)
        print '%s stopped successfully' % service
        time.sleep(3)
    elif action == 'start':
        win32serviceutil.StartService(service, machine)
        print '%s started successfully' % service
        time.sleep(3)
    elif action == 'restart':
        win32serviceutil.RestartService(service, machine)
        print '%s restarted successfully' % service
        time.sleep(3)
    elif action == 'status':
        if win32serviceutil.QueryServiceStatus(service, machine)[1] == 4:
            print "%s is running normally" % service
        else:
            print "%s is *not* running" % service

This function could be accessed by another program by importing the module, but in this case we want to be able to run the program, so some code is added at the bottom of the program to run the function multiple times, with different parameters:

machine = 'localhost'
service = 'RemoteRegistry'

service_info('start', machine, service)
service_info('stop', machine, service)
service_info('start', machine, service)
service_info('restart', machine, service)
service_info('status', machine, service)

When the program is run, it generates the following output:

RemoteRegistry started successfully
RemoteRegistry stopped successfully
RemoteRegistry started successfully
RemoteRegistry restarted successfully
RemoteRegistry is running normally

The following example enumerates the users, groups, shares, and servers found on a computer. In this example, it simply searches the local machine, but it could easily be modified to enable selecting and authenticating to a remote computer:

import win32net

#print users
users = win32net.NetUserEnum('localhost', 0)
print "USERS"
print "=========="
for user in users[0]:
    print user['name'] + "
"

#print groups
groups = win32net.NetGroupEnum('localhost', 0)
print "GROUPS"
print "=========="
for group in groups[0]:
    print group['name'] + "
"

#print shares
shares = win32net.NetShareEnum('localhost', 0)
print "SHARES"
print "=========="
for share in shares[0]:
    print share['netname'] + "
"

#print servers
servers = win32net.NetServerEnum(None, 100)
print "SERVERS"
print "=========="
for server in servers[0]:
    print server['name'] + "
"

As you can see, the win32net module provides functions that enable you to enumerate different network objects. It also enables you to perform other operations, such as the following:

The results returned depend entirely on the particular information found, but here is the output that resulted from running the script on my system:

I:Applied_PythonChapter_9>python win32net-example1.py
USERS
==========
Administrator
Guest
jim
jim user
__vmware_user__

GROUPS
==========
None

SHARES
==========
ADMIN$
C$
IPC$
share of jim

SERVERS
==========
JIM-PC

The following example shows the termios module being used to accept a password without echoing the password to the screen, and returning the password to the caller:

def getpass(prompt = "Password: "):
    import termios, sys
    fd = sys.stdin.fileno()
    old = termios.tcgetattr(fd)
    new = termios.tcgetattr(fd)
    new[3] = new[3] & ~termios.ECHO          # lflags
    try:
        termios.tcsetattr(fd, termios.TCSADRAIN, new)
        passwd = raw_input(prompt)
    finally:
        termios.tcsetattr(fd, termios.TCSADRAIN, old)
    return passwd

password = getpass()
if password == "zanzibar":
       print "Let you in"
else:
       print "Access denied"

The example makes use of the getrusage() function. It returns a tuple that contains 16 different data items related to system resource usage. The following table shows all the data items returned.

Here is the entire example:

import resource

resourcelist = ['time in user mode',
'time in system mode',
'maximum resident set size',
'shared memory size',
'unshared memory size',
'unshared stack size',
'page faults not requiring I/O',
'page faults requiring I/O',

'number of swap outs',
'block input operations',
'block output operations',
'messages sent',
'messages received',
'signals received',
'voluntary context switches',
'involuntary context switches']

getresource = resource.getrusage(resource.RUSAGE_SELF)

for i, item in enumerate(resourcelist):
       print item, ": ", getresource[i]

Now let's go through the example. First, a list is created with the text for all the items:

resourcelist = ['time in user mode',
'time in system mode',
'maximum resident set size',
'shared memory size',
'unshared memory size',
'unshared stack size',
'page faults not requiring I/O',
'page faults requiring I/O',
'number of swap outs',
'block input operations',
'block output operations',
'messages sent',
'messages received',
'signals received',
'voluntary context switches',
'involuntary context switches']

Then the getrusage() function is run, and its output is assigned to the list getresource:

getresource = resource.getrusage(resource.RUSAGE_SELF)

Finally, a for loop is used to output the information to the screen in a readable way:

for i, item in enumerate(resourcelist):
       print item, ": ", getresource[i]

When the program is run, the output looks like this:

time in user mode :   0.016001
time in system mode :   0.008
maximum resident set size :  0
shared memory size :   0
unshared memory size :   0
unshared stack size :   0
page faults not requiring I/O :  733
page faults requiring I/O :   0
number of swap outs :   0
block input operations :   0
block output operations :   0
messages sent :   0
messages received :   0
signals received :   0
voluntary context switches :   1
involuntary context switches :   4

The following example enables users to choose a log priority and enter a message. It then reports the status of the attempt to write to the syslog:

import syslog

print """
Enter a number and press [Enter]:
1 - Emergency
2 - Alert
3 - Critical
4 - Error
5 - Warning
6 - Notics
7 - Info
8 - Debug
"""
choice = raw_input("")

message = raw_input("Type the log message and press [Enter]: ")

if choice == '1':
       log_priority = syslog.LOG_EMERG

elif choice == '2':
       log_priority = syslog.LOG_ALERT
elif choice == '3':
       log_priority = syslog.LOG_CRIT
elif choice == '4':
       log_priority = syslog.LOG_ERR
elif choice == '5':
       log_priority = syslog.LOG_WARNING
elif choice == '6':
       log_priority = syslog.LOG_NOTICE
elif choice == '7':
       log_priority = syslog.LOG_INFO
elif choice == '8':
       log_priority = syslog.LOG_DEBUG

try:
       syslog.syslog(log_priority, message)
       print "log entry recorded"
except:
       print "problem writing to syslog"
       raise

The first section of the program simply presents a menu so that the user can choose a log priority:

print """
Enter a number and press [Enter]:
1 - Emergency
2 - Alert
3 - Critical
4 - Error
5 - Warning
6 - Notics
7 - Info
8 - Debug
"""
choice = raw_input("")

Then the user is prompted for the message to be written to the log:

message = raw_input("Type the log message and press [Enter]: ")

Based on the user's selection, the program then assigns the log priority:

if choice == '1':
       log_priority = syslog.LOG_EMERG
elif choice == '2':
       log_priority = syslog.LOG_ALERT
elif choice == '3':
       log_priority = syslog.LOG_CRIT
elif choice == '4':
       log_priority = syslog.LOG_ERR
elif choice == '5':
       log_priority = syslog.LOG_WARNING
elif choice == '6':
       log_priority = syslog.LOG_NOTICE
elif choice == '7':
       log_priority = syslog.LOG_INFO
elif choice == '8':
       log_priority = syslog.LOG_DEBUG

Finally, the syslog is written to, and the status is returned:

try:
        syslog.syslog(log_priority, message)
        print "log entry recorded"
except:
        print "problem writing to syslog"
        raise

Following is an example showing each of the functions in action:

import commands

print r"output of commands.getstatusoutput('ls /usr/local')"
output1 = commands.getstatusoutput('ls /usr/local')
print output1
print ""

print r"output of commands.getstatusoutput('cat /bin/junk')"
output2 = commands.getstatusoutput('cat /bin/junk')
print output2
print ""

print r"output of commands.getoutput('ls /usr/local')"
output3 = commands.getoutput('ls /usr/local')
print output3
print ""

print r"output of commands.getstatus('/usr/local')"
output4 = commands.getstatus('/usr/local')
print output4
print ""

Here is what the screen output looks like for this example:

output of commands.getstatusoutput('ls /usr/local')
(0, 'bin
etc
games
include
lib
man
sbin
share
src')

output of commands.getstatusoutput('cat /bin/junk')
(256, 'cat: /bin/junk: No such file or directory')

output of commands.getoutput('ls /usr/local')
bin
etc
games
include
lib
man
sbin
share
src

output of commands.getstatus('/usr/local')
drwxr-xr-x 10 root root 4096 2007-10-16 01:17 /usr/local