An introduction to python given at the Computer Science departmental seminar at Otago University, NZ on the 27th March 2009.

1. Introduction
to
Python

2. Aim of this talk
Show you that Python is not a noddy language

Get you interested in learning Python

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3. Before we start
Who am I?
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4. Tim Penhey
Otago University Comp Sci 1991­1994

Intermittent contractor for 12 years
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Started working for Canonical over 2 years ago
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First started with Python 8 years ago after

reading “The Cathedral & the Bazaar”
Python has been my primary development

language for around three years now
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5. 5

6. Quick Question
What languages are you tought as an

undergraduate now?
When I was here we did: Pascal; Modula­2;

LISP; Prolog; Assembly; C; Haskell; ML; Ada;
and Objective C (kinda)
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7. Python
Not named after this...
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8. 8

9. Python
... but this ...
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10. 10

11. Python
... by this man ...
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12. 12

13. Guido van Rossum
Python's BDFL

http://www.python.org/~guido/
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Blog http://neopythonic.blogspot.com/
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Now works for Google

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14. Python History
Implementation started Dec 1989
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Feb 1991 released to alt.sources
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Jan 1994 1.0.0 released
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Oct 2000 2.0 released
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Oct 2008 2.6 released
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Dec 2008 3.0 released
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2.7 and 3.1 in development
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15. Python has...
very clear, readable syntax
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strong introspection capabilities
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intuitive object orientation
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natural expression of procedural code
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full modularity, supporting hierarchical
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packages
exception­based error handling
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16. Python has...
very high level dynamic data types
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an extensive standard libraries and third party
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modules for virtually every task
extensions and modules easily written in C,

C++ (or Java for Jython, or .NET languages for
IronPython)
the ability to be embedded within applications

as a scripting interface
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17. Python plays well with others
Python can integrate with COM, .NET, and

CORBA objects
Jython is Python for the JVM and can interact
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fully with Java classes
IronPython is Python for .NET
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Well supported in the Internet Communication

Engine (ICE ­ http://zeroc.com)
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18. Python runs everywhere
All major operating systems
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Windows
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Linux/Unix
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Mac
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And some lesser ones
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OS/2
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Amiga
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Nokia Series 60 cell phones
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19. Python is Open
Implemented under an open source license
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Freely usable and distributable, even for

commercial use.
Python Enhancement Proposals – PEP
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propose new features
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collecting community input
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documenting decisions
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20. My Python Favourites #1
The Zen of Python
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PEP 20
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Long time Pythoneer Tim Peters succinctly
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channels the BDFL's guiding principles for Python's
design into 20 aphorisms, only 19 of which have
been written down.
aphorism – A tersely phrased statement of a

truth or opinion
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21. The Zen of Python
Beautiful is better than ugly.
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22. The Zen of Python
Explicit is better than implicit.
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23. The Zen of Python
Simple is better than complex.
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24. The Zen of Python
Complex is better than
complicated.
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25. The Zen of Python
Flat is better than nested.
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26. The Zen of Python
Sparse is better than dense.
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27. The Zen of Python
Readability counts.
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28. The Zen of Python
Special cases aren't special
enough to break the rules.
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29. The Zen of Python
Although practicality beats
purity.
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30. The Zen of Python
Errors should never pass
silently.
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31. The Zen of Python
Unless explicitly silenced.
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32. The Zen of Python
In the face of ambiguity, refuse
the temptation to guess.
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33. The Zen of Python
There should be one — and
preferably only one — obvious
way to do it.
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34. The Zen of Python
Although that way may not be
obvious at first unless you're
Dutch.
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35. The Zen of Python
Now is better than never.
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36. The Zen of Python
Although never is often better
than right now.
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37. The Zen of Python
If the implementation is hard to
explain, it's a bad idea.
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38. The Zen of Python
If the implementation is easy to
explain, it may be a good idea.
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39. The Zen of Python
Namespaces are one honking
great idea — let's do more of
those!
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40. Hello World
Python 2.6
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print “Hello World”
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Pyton 3.0
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print(“Hello World”)
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41. My Python Favourites #2
The interactive interpreter
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42. Datatypes
All the usual suspects
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Strings (Unicode)
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int
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bool
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float (only one real type)
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complex
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files
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43. Unusual Suspects
long — automatic promotion from int if needed
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>>> x = 1024
>>> x ** 50
327339060789614187001318969682759915221
664204604306478948329136809613379640467
455488327009232590415715088668412756007
1009217256545885393053328527589376L
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44. Built­in datastructures
Tuples – Fixed Length
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(1, 2, 3, “Hello”, False)
Lists
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[1, 2, 4, “Hello”, False]
Dictionaries
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{42: “The answer”, “key”: “value”}
Sets
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set([“list”, “of”, “values”])
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45. Functions
Python uses whitespace to determine blocks of

code (please don't use tabs)
def greet(person):
if person == “Tim”:
print “Hello Master”
else:
print “Hello %s” % person
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46. Parameter Passing
Order is important unless using the name
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def foo(name, age, address)
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foo('Tim', address='Home', age=36)
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Default arguments are supported
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def greet(name='World')
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Variable length args acceptable as a list or dict
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def foo(*args, **kwargs)
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47. Classes
class MyClass:
quot;quot;quot;This is a docstring.quot;quot;quot;
name = quot;Ericquot;
def say(self):
return quot;My name is %squot; % self.name
instance = MyClass()
print instance.say()
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48. Modules
Any python file is considered a module
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Modules are loaded from the PYTHONPATH
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Nested modules are supported by using
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directories.
~/src/lazr/enum/__init__.py
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If PYTHONPATH includes ~/src
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import lazr.enum
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49. Exceptions
Also used for flow control – StopIteration
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Exceptions are classes, and custom exceptions
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are easy to write to store extra state information
raise SomeException(params)
try:
# Do stuff
except Exception, e:
# Do something else
finally:
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# Occurs after try and except block

50. Duck Typing
If it walks like a duck and quacks like a duck, I
would call it a duck – James Whitcomb Riley
There is no function or method overriding
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Methods can be checked using getattr
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Consider zope.interface
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51. Batteries Included
The Python standard library is very extensive
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regular expressions, codecs
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date and time, collections, theads and mutexs
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OS and shell level functions (mv, rm, ls)
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Support for SQLite and Berkley databases
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zlib, gzip, bz2, tarfile, csv, xml, md5, sha
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logging, subprocess, email, json
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httplib, imaplib, nntplib, smtplib
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and much, much more
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52. Metaprogramming
Descriptors
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Decorators
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Meta­classes
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53. My Python Favourites #3
The Python debugger
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import pdb;
pdb.set_trace()
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54. Other Domains
Asynchronous Network Programming
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Twisted framework ­ http://twistedmatrix.com
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Scientific and Numeric
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Bioinformatics ­ biopython
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Linear algebra, signal processing – SciPy
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Fast compact multidimensional arrays – NumPy
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Desktop GUIs
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wxWidgets, GTK+, Qt
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55. What is Python bad at?
Anything that requires a lot of mathmatical

computations
Anything that wants to use threads across
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cores or CPUs
Real­time systems
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56. Work arounds
Write extension libraries in C or C++
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Use multiple processes instead of multiple

threads
Use a different language
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57. NZ Python Users Group
http://nzpug.org
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Regional meetings, DunPUG
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Mailing list using google groups
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Planning KiwiPyCon
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2 day event over a weekend in Christchurch
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7­8 November 2009 (that's this year!)
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58. Questions?
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