Home > Articles > Open Source > Python

Python Libraries

Generic Operational System

This group of services provides interfaces to operating system features that you can use in almost every platform. Most of Python's operating system modules are based on the Posix interface.

os

The os module is a portable OS API that searches for Operating-System–dependent built-in modules (mac, posix, nt), and exports their functionality using the same interface. Certain tools are available only on platforms that support them. However, it is highly recommended that you use this module instead of the platform-specific modules, which are really an implementation detail of os. By using the os module, you make your program more portable.

os.environ

This is a dictionary that contains all the environment variables.

You can search for a specific variable:

>>> import os
>>> path = os.environ["PATH"] #USER, EDITOR, etc...

or list all of them:

>>> for key in os.environ.keys():
...  print key, " = " , os.environ[key]
...

os.name

It returns the name of the current system.

>>> name = os.name  # "posix","dos","mac","nt"
nt

os.getcwd()

This function returns the current working directory.

>>> os.getcwd()
'C:\\Program Files\\Python'

os.curdir

This is a simple constant that returns the OS-specific string used to identify the current directory.

>>> os.curdir
'.'

os.listdir()

If directory is omitted, it lists the filenames of the current directory. Otherwise, it lists the filenames of directory.

basic syntax: os.listdir([directory])

>>> files = os.listdir(os.curdir)

os.rename()

It renames a file.

basic syntax: os.rename(oldfile, newfile)

os.chmod()

It changes the file mode. This is a UNIX command.

basic syntax: os.chmod(file, mode)

os.system()

It opens an Operating System subshell and executes the command.

basic syntax: os.system(command)

>>> os.system("rm -rf " + filename)

os.popen()

This is a UNIX function that returns a file-like object. It allows you to execute a shell command and read the standard output of external pipes (by setting mode to r) or write to their standard input (by setting mode to w). The default mode is r. Note that even though popen is a UNIX function, it is also implemented on the other Python ports.

basic syntax: os.popen(shell command, mode)

>>> file = os.popen('sed \'s/yes/no/g' > output','w')
>>> file.write("yes\n")
>>>
>>> file = os.popen('cat manual.txt', 'r')
>>> f = file.read()

os.remove()

It deletes a file.

basic syntax: os.remove(file)

os.mkdir()

It creates a new directory.

basic syntax: os.mkdir(directory)

os.rmdir()

It removes an existing directory.

basic syntax: os.rmdir(directory)

os.removedirs()

It is a wrapper for rmdir that deletes everything under the directory.

basic syntax: os.removedirs(directory)

os.path

The os.path is a module imported by the os module that exposes useful common functions to manipulate pathnames. Remember that you don't have to explicitly import os.path. You get it for free when you import os.

os.path.exists()

It returns true if path really exists.

basic syntax: os.path.exists(path)

os.path.isfile()

It returns true if the specified path is a file.

basic syntax: os.path.isfile(path)

os.path.isdir()

It returns true if the specified path is a directory.

basic syntax: os.path.isdir(path)

os.path.split()

It splits filename, returning a tuple that contains the directory structure and filename, which together combine the original filename argument.

basic syntax: os.path.split(filename)

dircache

The dircache module reads directory listings using a cache. Note that this module will be replaced by the new module filecmp in Python 1.6.

stat

The stat module works along with the os module by interpreting information about existing files that is extracted by the os.stat() function and stored on a tuple structure. This tuple contains the file size, the file owner group, the file owner name, the last accessed and last modified dates, and its mode.

statcache

The statcache module is a simple optimization of the os.stat() function.

statvfs

The statvfs module stores constants that are used to interpret the results of a call to the os.statvfs() function. By the way, the os.statvfs provides information about your file system.

>>> import statvfs, os
>>> stat = os.statvfs(".")
>>> maxfnl = stat[statvfs.F_NAMEMAX]
>>> print "%d is the maximum file name length" % maxfnl
>>> print "that is allowed on your file system."
255

cmp

The cmp module is used to compare files. Note that this module will be replaced by the new module filecmp in Python 1.6.

cmpcache

The cmpcache module is a more efficient version of the cmp module for file comparisons. Note that this module will be replaced by the new module filecmp in Python 1.6.

time

The time module exposes functions for time access and conversion. It is important to remember that there are no Year 2000 issues in the Python language.

time.time()

It returns the current timestamp in seconds since the UNIX epoch began (start of 1970, UTC - Universal Time Coordinated).

basic syntax: time.time()

time.localtime()

It converts a time expressed in seconds into a time tuple. This tuple has the following format: (4digitsyear, month, day, hour, minute, second, day of week, day of year, daylight savings flag).

basic syntax: time.locatime(seconds)

time.asctime()

It converts a time tuple into a 24-character string.

basic syntax: time.asctime(tuple)

>>> import time
>>> time.time()
957044415.14
>>> time.localtime(time.time())
(2000, 4, 29, 17, 42, 14, 5, 120, 1)
>>> time.asctime(time.localtime(time.time()))
'Sat Apr 29 17:42:59 2000'

time.sleep()

It suspends the execution of a program for a specific number of seconds.

basic syntax: time.sleep(seconds)

>>> import time
>>> time.sleep(10)  # waits for 10 seconds

sched

The sched module implements a general-purpose event scheduler.

getpass

The getpass module implements a portable function that enables the user to type a password without echoing the entry in the screen.

basic syntax: getpass.getpass([prompt])

This module also provides a function to collect information about the user's login.

basic syntax: getpass.getuser()

import getpass
defaultpwd = "Ahhhhh"
user = getpass.getuser()
print "Hello %s," % user
pass = getpass.getpass("Please, type the password. ")
if pass == defaultpwd:
  print "Welcome back to the system!!
else:
  print r"You've just activated the detonation process.Sorry"

curses

The curses module is a terminal independent I/O interface to the curses UNIX library.

For more details, check out the curses HOWTO at http://py-howto.sourceforge.net/curses/curses.html.

getopt

The getopt module is a parser for command-line options and arguments (sys.argv). This module provides the standard C getopt functionality.

1: >>> import getopt
2: >>> args = ['-h','-r','origin.txt','—file','work.txt','755','777']
3: >>> opts, pargs = getopt.getopt(args, 'hr:', ['file='])
4: >>> opts
5: [('-h', ''), ('-r','origin.txt') , ('—file','work.txt')]
6: >>> pargs
7: ['755','777']

Before transporting arguments to this function, line 2 shows you that single options must be preceded by a single hyphen and long options must be preceded by double hyphens.

In line 3, note that single options that require an argument must end with a colon. On the other hand, long options that require an argument must end with an equal sign.

The getopt.getopt() returns two values: A tuple that contains pairs of (option, argument) values (line 5), and a list of standalone arguments that aren't associated with any options (line 7).

tempfile

The tempfile module generates unique temporary filenames based on templates defined by the variables tempfile.tempdir and tempfile.template.

tempfile.mktemp()

This function returns a temporary filename. It doesn't physically create or remove files.

basic syntax: filename = tempfile.mktemp()

>>> import tempfile, os
>>> temp = tempfile.mktemp()
>>> open(temp, 'w')
>>> os.close(file)
>>> os.remove(file)

tempfile.TemporaryFile()

This function returns a file object that is saved in your temporary local folder (/tmp or c:/temp, for example). The system removes this file after it gets closed.

basic syntax: fileobject = tempfile.TemporaryFile()

errno

The errno module makes available the standard errno system symbols, such as EACCES, EADDRINUSE, and EDEADLOCK.

Each symbol is associated to a constant error code value.

>>> import errno
>>> errno.ELOOP
10062

More information about this module and its symbols is provided in Chapter 4.

glob

The glob module finds and returns pathnames matching a specific pattern, just like the UNIX shell does.

basic syntax: glob.glob(pattern)

>>> import glob
>>> lst = glob.glob("c:\\*.txt")
>>> print lst
['c:\\FRUNLOG.TXT', 'c:\\DETLOG.TXT', 'c:\\BOOTLOG.TXT', 'c:\\SETUPLOG.TXT',
 'c:\\NETLOG.TXT', 'c:\\RESETLOG.TXT']

fnmatch

The fnmatch module uses wildcards to provide support for UNIX shell-style filename pattern matching. These wildcards are different from those normally used by the re module.

fnmatch.fnmatch()

This function returns 1 (true) if the provided filename matches the pattern defined.

basic syntax: fnmatch.fnmatch(filename, pattern)

>>> import fnmatch
>>> fnmatch.fnmatch("foo.gif", "*.gif")
1

fnmatch.translate()

This function converts a fnmatch-style pattern into a regular expression.

basic syntax: variable = fnmatch.translate(pattern)

>>> import fnmatch
>>> regexpr = fnmatch.translate("*.txt")
>>> print regexpr
.*\.txt$

shutil

The shutil module provides high-level file operations. Essentially, it offers many file-copying functions and one directory removal function.

shutil.copyfile()

It makes a straight binary copy of the source file, calling it newcopy.

basic syntax: shutil.copyfile(source, newcopy)

shutil.rmtree()

It deletes the path directory, including all of its subdirectories, recursively. If ignore_errors is set to 0, errors are ignored. Otherwise, the onerror function argument is called to handle the error. If the clause onerror is set to None, an exception is raised when an error occurs.

basic syntax: shutil.rmtree(path, ignore_errors=0, onerror=None)

locale

The locale module provides access to the POSIX locale mechanism, enabling internationalization services. This module defines a set of parameters that describe the representation of strings, time, numbers, and currency.

The good thing about using this module is that programmers don't have to worry about the specifics of each country where their applications are executed.

mutex

The mutex module defines a mutex class that allows mutual-exclusion support via acquiring and releasing locks.

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020