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An introduction to python given at the Computer Science departmental seminar at Otago University, NZ on the 27th March 2009.
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Introductionto
Python
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Aim of this talk
Show you that Python is not a noddy language
Get you interested in learning Python
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Before we start
Who am I?
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Tim Penhey
Otago University Comp Sci 19911994 Intermittent contractor for 12 years Started working for Canonical over 2 years ago 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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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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Python
Not named after this...
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Python
... but this ...
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Python
... by this man ...
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Guido van Rossum
Python's BDFL http://www.python.org/~guido/ Blog http://neopythonic.blogspot.com/ Now works for Google
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Python History
Implementation started Dec 1989 Feb 1991 released to alt.sources Jan 1994 1.0.0 released Oct 2000 2.0 released Oct 2008 2.6 released Dec 2008 3.0 released
2.7 and 3.1 in development
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Python has...
very clear, readable syntax strong introspection capabilities intuitive object orientation natural expression of procedural code full modularity, supporting hierarchical
packages exceptionbased error handling
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Python has...
very high level dynamic data types an extensive standard libraries and third party
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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Python plays well with others
Python can integrate with COM, .NET, and CORBA objects
Jython is Python for the JVM and can interact fully with Java classes
IronPython is Python for .NET Well supported in the Internet Communication
Engine (ICE http://zeroc.com)
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Python runs everywhere
All major operating systems Windows Linux/Unix Mac
And some lesser ones OS/2 Amiga Nokia Series 60 cell phones
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Python is Open
Implemented under an open source license Freely usable and distributable, even for
commercial use.
Python Enhancement Proposals – PEP propose new features collecting community input documenting decisions
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My Python Favourites #1
The Zen of Python PEP 20 Long time Pythoneer Tim Peters succinctly
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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The Zen of Python
Beautiful is better than ugly.
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The Zen of Python
Explicit is better than implicit.
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The Zen of Python
Simple is better than complex.
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The Zen of Python
Complex is better than complicated.
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The Zen of Python
Flat is better than nested.
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The Zen of Python
Sparse is better than dense.
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The Zen of Python
Readability counts.
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The Zen of Python
Special cases aren't special enough to break the rules.
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The Zen of Python
Although practicality beats purity.
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The Zen of Python
Errors should never pass silently.
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The Zen of Python
Unless explicitly silenced.
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The Zen of Python
In the face of ambiguity, refuse the temptation to guess.
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The Zen of Python
There should be one — and preferably only one — obvious
way to do it.
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The Zen of Python
Although that way may not be obvious at first unless you're
Dutch.
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The Zen of Python
Now is better than never.
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The Zen of Python
Although never is often better than right now.
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The Zen of Python
If the implementation is hard to explain, it's a bad idea.
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The Zen of Python
If the implementation is easy to explain, it may be a good idea.
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The Zen of Python
Namespaces are one honking great idea — let's do more of
those!
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Hello World
Python 2.6 print “Hello World”
Pyton 3.0 print(“Hello World”)
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My Python Favourites #2
The interactive interpreter
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Datatypes
All the usual suspects Strings (Unicode) int bool float (only one real type) complex files
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Unusual Suspects
long — automatic promotion from int if needed
>>> x = 1024
>>> x ** 50
3273390607896141870013189696827599152216642046043064789483291368096133796404674554883270092325904157150886684127560071009217256545885393053328527589376L
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Builtin datastructures
Tuples – Fixed Length
(1, 2, 3, “Hello”, False) Lists
[1, 2, 4, “Hello”, False] Dictionaries
{42: “The answer”, “key”: “value”} Sets
set([“list”, “of”, “values”])
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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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Parameter Passing
Order is important unless using the name def foo(name, age, address) foo('Tim', address='Home', age=36)
Default arguments are supported def greet(name='World')
Variable length args acceptable as a list or dict def foo(*args, **kwargs)
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Classes
class MyClass:
"""This is a docstring."""
name = "Eric"
def say(self):
return "My name is %s" % self.name
instance = MyClass()
print instance.say()
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Modules
Any python file is considered a module Modules are loaded from the PYTHONPATH Nested modules are supported by using
directories. ~/src/lazr/enum/__init__.py
If PYTHONPATH includes ~/src import lazr.enum
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Exceptions
Also used for flow control – StopIteration Exceptions are classes, and custom exceptions
are easy to write to store extra state informationraise SomeException(params)
try:
# Do stuff
except Exception, e:
# Do something else
finally:
# Occurs after try and except block
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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 Methods can be checked using getattr Consider zope.interface
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Batteries Included
The Python standard library is very extensive regular expressions, codecs date and time, collections, theads and mutexs OS and shell level functions (mv, rm, ls) Support for SQLite and Berkley databases zlib, gzip, bz2, tarfile, csv, xml, md5, sha logging, subprocess, email, json httplib, imaplib, nntplib, smtplib and much, much more
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Metaprogramming
Descriptors
Decorators
Metaclasses
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My Python Favourites #3
The Python debugger
import pdb;
pdb.set_trace()
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Other Domains
Asynchronous Network Programming Twisted framework http://twistedmatrix.com
Scientific and Numeric Bioinformatics biopython Linear algebra, signal processing – SciPy Fast compact multidimensional arrays – NumPy
Desktop GUIs wxWidgets, GTK+, Qt
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What is Python bad at?
Anything that requires a lot of mathmatical computations
Anything that wants to use threads across cores or CPUs
Realtime systems
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Work arounds
Write extension libraries in C or C++
Use multiple processes instead of multiple threads
Use a different language
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NZ Python Users Group
http://nzpug.org Regional meetings, DunPUG Mailing list using google groups Planning KiwiPyCon
2 day event over a weekend in Christchurch 78 November 2009 (that's this year!)
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Questions?
