Python Intro

Introduction to Python

Aim of this talk Show you that Python is not a noddy language  Get you interested in learning Python  2

Before we start Who am I? 3

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 4

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) 6

Python Not named after this... 7

Python ... but this ... 9

Python ... by this man ... 11

Guido van Rossum Python's BDFL  http://www.python.org/~guido/  Blog http://neopythonic.blogspot.com/  Now works for Google  13

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  14

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  15

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 16

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) 17

Python runs everywhere All major operating systems  Windows  Linux/Unix  Mac  And some lesser ones  OS/2  Amiga  Nokia Series 60 cell phones  18

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  19

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 20

The Zen of Python Beautiful is better than ugly. 21

The Zen of Python Explicit is better than implicit. 22

The Zen of Python Simple is better than complex. 23

The Zen of Python Complex is better than complicated. 24

The Zen of Python Flat is better than nested. 25

The Zen of Python Sparse is better than dense. 26

The Zen of Python Readability counts. 27

The Zen of Python Special cases aren't special enough to break the rules. 28

The Zen of Python Although practicality beats purity. 29

The Zen of Python Errors should never pass silently. 30

The Zen of Python Unless explicitly silenced. 31

The Zen of Python In the face of ambiguity, refuse the temptation to guess. 32

The Zen of Python There should be one — and preferably only one — obvious way to do it. 33

The Zen of Python Although that way may not be obvious at first unless you're Dutch. 34

The Zen of Python Now is better than never. 35

The Zen of Python Although never is often better than right now. 36

The Zen of Python If the implementation is hard to explain, it's a bad idea. 37

The Zen of Python If the implementation is easy to explain, it may be a good idea. 38

The Zen of Python Namespaces are one honking great idea — let's do more of those! 39

Hello World Python 2.6  print “Hello World”  Pyton 3.0  print(“Hello World”)  40

My Python Favourites #2 The interactive interpreter  41

Datatypes All the usual suspects  Strings (Unicode)  int  bool  float (only one real type)  complex  files  42

Unusual Suspects long — automatic promotion from int if needed  >>> x = 1024 >>> x ** 50 327339060789614187001318969682759915221 664204604306478948329136809613379640467 455488327009232590415715088668412756007 1009217256545885393053328527589376L 43

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”]) 44

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 45

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)  46

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() 47

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  48

Exceptions Also used for flow control – StopIteration  Exceptions are classes, and custom exceptions  are easy to write to store extra state information raise SomeException(params) try: # Do stuff except Exception, e: # Do something else finally: 49 # Occurs after try and except block

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  50

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  51

Metaprogramming Descriptors  Decorators  Metaclasses  52

My Python Favourites #3 The Python debugger  import pdb; pdb.set_trace() 53

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  54

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  55

Work arounds Write extension libraries in C or C++  Use multiple processes instead of multiple  threads Use a different language  56

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!)  57

Questions? 58

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Python Intro

by Tim Penhey

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