Common utility scripts often need to process command line arguments. These
arguments are stored in the
sys module's argv attribute as a list.
For instance the following output results from running "python
demo.py one two three" at the command line:
random module provides tools for making random
>>> import random
>>> random.choice(['apple', 'pear', 'banana'])
>>> random.sample(xrange(100), 10) # sampling without replacement
[30, 83, 16, 4, 8, 81, 41, 50, 18, 33]
>>> random.random() # random float
>>> random.randrange(6) # random integer chosen from range(6)
There are a number of modules for accessing the internet and processing
internet protocols. Two of the simplest are
urllib2 for retrieving data from urls and
smtplib for sending mail:
>>> import urllib2
>>> for line in urllib2.urlopen('http://tycho.usno.navy.mil/cgi-bin/timer.pl'):
... if 'EST' in line or 'EDT' in line: # look for Eastern Time
... print line
<BR>Nov. 25, 09:43:32 PM EST
>>> import smtplib
>>> server = smtplib.SMTP('localhost')
>>> server.sendmail('email@example.com', 'firstname.lastname@example.org',
Beware the Ides of March.
Dates and Times
The datetime module supplies classes for manipulating
dates and times in both simple and complex ways. While date and time arithmetic
is supported, the focus of the implementation is on efficient member extraction
for output formatting and manipulation. The module also supports objects that
are timezone aware.
# dates are easily constructed and formatted
>>> from datetime import date
>>> now = date.today()
datetime.date(2003, 12, 2)
>>> now.strftime("%m-%d-%y. %d %b %Y is a %A on the %d day of %B.")
'12-02-03. 02 Dec 2003 is a Tuesday on the 02 day of December.'
# dates support calendar arithmetic
>>> birthday = date(1964, 7, 31)
>>> age = now - birthday
Common data archiving and compression formats are directly supported by
>>> import zlib
>>> s = 'witch which has which witches wrist watch'
>>> t = zlib.compress(s)
'witch which has which witches wrist watch'
Some Python users develop a deep interest in knowing the relative performance
of different approaches to the same problem. Python provides a measurement tool
that answers those questions immediately.
For example, it may be tempting to use the tuple packing and unpacking
feature instead of the traditional approach to swapping arguments. The
timeit module quickly demonstrates a modest
In contrast to timeit's fine level of granularity,
profile and pstats modules
provide tools for identifying time critical sections in larger blocks of code.
One approach for developing high quality software is to write tests for each
function as it is developed and to run those tests frequently during the
doctest module provides a tool for scanning a module
and validating tests embedded in a program's docstrings. Test construction is as
simple as cutting-and-pasting a typical call along with its results into the
docstring. This improves the documentation by providing the user with an example
and it allows the doctest module to make sure the code remains true to the
"""Computes the arithmetic mean of a list of numbers.
>>> print average([20, 30, 70])
return sum(values, 0.0) / len(values)
doctest.testmod() # automatically validate the embedded tests
unittest module is not as effortless as the
doctest module, but it allows a more comprehensive set
of tests to be maintained in a separate file:
self.assertEqual(average([20, 30, 70]), 40.0)
self.assertEqual(round(average([1, 5, 7]), 1), 4.3)
self.assertRaises(ZeroDivisionError, average, )
self.assertRaises(TypeError, average, 20, 30, 70)
unittest.main() # Calling from the command line invokes all tests
Python has a ``batteries included'' philosophy. This is best seen through the
sophisticated and robust capabilities of its larger packages. For example:
SimpleXMLRPCServer modules make implementing
remote procedure calls into an almost trivial task. Despite the modules
names, no direct knowledge or handling of XML is needed.
email package is a library for managing email
messages, including MIME and other RFC 2822-based message documents. Unlike
smtplib and poplib which
actually send and receive messages, the email package has a complete toolset
for building or decoding complex message structures (including attachments)
and for implementing internet encoding and header protocols.
xml.sax packages provide robust support for
parsing this popular data interchange format. Likewise, the
csv module supports direct reads and writes in a
common database format. Together, these modules and packages greatly
simplify data interchange between python applications and other tools.
Internationalization is supported by a number of modules including
locale, and the