Programming Under Linux In Python

Programming Under Linux In Python Marwan Osman [email_address]

Agenda
What is Python ???
Why Python ???
Syntax Walkthroughs
Linux and Python

What is Python ???
What is Python ???
Why Python ???
Syntax Walkthroughs
Linux and Python

History
Created by Guido von Rossum in 1990 (BDFL)
named after Monty Python's Flying Circus
http://www.python.org/~guido/
Blog http://neopythonic.blogspot.com/
Now works for Google

What is Python ???
general-purpose high-level programming language, often used as a scripting language.
interpreted, interactive, object-oriented.
incorporates modules, exceptions, dynamic typing, very high level dynamic data types, and classes, automatic memory management.
remarkable power with very clear syntax.
has interfaces to many system calls and libraries, as well as to various window systems, and is extensible in C or C++.
usable as an extension language for applications that need a programmable interface.

What is Python ???
supports multiple programming paradigms (primarily object oriented, imperative, and functional)
portable: runs on many Unix variants, on the Mac, and on PCs under MS-DOS, Windows, Windows NT, OS/2, FreeBSD Solaris, OS/2, Amiga,AROS, AS/400, BeOS, OS/390, z/OS, Palm OS, QNX, VMS, Psion, Acorn RISC OS, VxWorks, PlayStation, Sharp Zaurus, Windows CE and even PocketPC !

What is Python ???
Developed and supported by a large team of volunteers - Python Software Foundation
Major implementations: CPython, Jython, Iron Python, PyPy
CPython - implemented in C, the primary implementation
Jython - implemented for the JVM
Pypy - implemented in Python
IronPython - implemented in C#, allows python to use the .NET libraries

Why Python ???
What is Python ???
Why Python ???
Syntax Walkthroughs
Linux and Python

Why Python ???
Readability, maintainability, very clear readable syntax
Fast development and all just works the first time...
very high level dynamic data types
Dynamic typing and automatic memory management
Paradigm of your choice
Free and open source
Implemented under an open source license. Freely usable and distributable, even for commercial use.
Simplicity , Great first language
Availability (cross-platform)
Interactivity (interpreted language)

Why Python ???
GUI support – GUIs typically developed with Tk
Strong introspection capabilities
Intuitive object orientation
Natural expression of procedural code
Full modularity, supporting hierarchical packages
Exceptionbased error handling
The ability to be embedded within applications as a scripting interface
Scalable – can play nicely with other languages

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 ...

Python Libraries
Biopython - Bioinformatics
SciPy - Linear algebra, signal processing
NumPy - Fast compact multidimensional arrays
PyGame - Game Development
Visual Python - real-time 3D output
Django - High-level python Web framework
and much more ...

E.g. Projects with Python
Websites: Google, YouTube, Yahoo Groups & Maps, CIA.gov
Appengine: http://code.google.com/appengine/
” Google: Python has been an important part of Google since the beginning.”, Peter Norvig.
Python application servers and Python scripting to create the web UI for BigTable (their database project)
Systems: NASA, LALN, CERN, Rackspace
Nasa Nebula http://nebula.nasa.gov/about
Games: Civilization 4, Quark (Quake Army Knife)
Mobile phones: Nokia S60 (Symbian), PythonCE
P2P: BitTorrent

Python Problems
Scripting-like language and compiled and runtime - hence slower than C/C+ + and slightly slower than Java
Memory economy hard to achieve (high level data-structures)
Relies on a locking mechanism called the Global Interpreter Lock (GIL) in multi-threading

Turn Arounds
Write extension libraries in C or C++
Use multiple processes instead of multiple threads
Use a different language
Use Stackless Python

Syntax Walkthroughs
What is Python ???
Why Python ???
Syntax Walkthroughs
Linux and Python

Hello World
Python 2.6
Python 3.0
print (“Hello World”) print “Hello World”

Basics
Numbers:
Integers: 4 , 8 , 15, 16 , 23 , 42 ,108
Floating point: 4.23 , 42.8E-4
Complex Numbers: -5+4j , 2.3 – 4.6j
Strings
Immutable , Unicode by default
Single quotes, double quotes ,triple quotes (multiline)
'Hello Word' , ”Hello World” , '''Hello World''' , ”””Hello World”””
Concatenation : 'What's ' 'your name?'
automatically converted in to "What's your name?”

Strings: format() >>>age = 25 >>>name = 'Swaroop' >>> print ( '{0} is {1} years old' .format(name, age)) Swaroop is 25 years old >>> '{0:.3}' .format( 1 / 3 ) '0.333' >>> '{0:_^11}' .format( 'hello' ) '___hello___' >>> '{name} wrote {book}' .format(name= 'Swaroop' , book= 'A Byte of Python' ) 'Swaroop wrote A Byte of Python'

Variables
Naming identifiers:
The first character be a letter of the alphabet (uppercase ASCII or lowercase ASCII or Unicode character) or an underscore ('_').
The rest of the identifier name can consist of letters (uppercase ASCII or lowercase ASCII or Unicode character), underscores ('_') or digits (0-9).
Identifier names are case-sensitive. For example, myname and myName are not the same.
Valid identifier e.g.: i, __my_name, name_23, a1b2_c3,
resumÃƒÆ’Ã†â€TMÃƒâ€ ¢â‚¬â„¢ÃƒÆ’¢â‚¬Å¡Ãƒâ€šÃ‚Â©_count.
invalid identifier e.g.: 2things, my-name

Indentation
Python uses whitespace to determine blocks of code
def greet (person): if person == “Tim”: print (“Hello Master”) else : print (“Hello {name}”.format(name=person))

Control Flow if guess == number: #do something elif guess < number: #do something else else : #do something else while True : #do something #break when done break else : #do something when the loop ends for i in range( 1 , 5 ): print (i) else : print ( 'The for loop is over' ) #1,2,3,4 for i in range( 1 , 5 , 2 ): print (i) else : print ( 'The for loop is over' ) #1,3

Data Structures
List
Mutable data type, array-like
[1, 2, 4, “Hello”, False]
list.sort() ,list.append() ,len(list), list[i]
Tuple
Immutable data type, faster than lists
(1, 2, 3, “Hello”, False)
Dictionary
{42: “The answer”, “key”: “value”}
Set
([“list”, “of”, “values”])

Functions
Order is important unless using the name
Default arguments are supported
def sayHello (): print ( 'Hello World!' ) def foo (name, age, address) : pass foo( 'Tim' , address= 'Home' , age= 36 ) def greet (name= 'World' )

Functions
Variable length args acceptable as a list or dict
def total (initial= 5 , *numbers, **keywords): count = initial for number in numbers: count += number for key in keywords: count += keywords[key] return count print (total( 10 , 1 , 2 , 3 , vegetables= 50 , fruits= 100 ))

Functions def printMax (x, y): '''Prints the maximum of two numbers. The two values must be integers.''' x = int(x) # convert to integers, if possible y = int(y) if x > y: r eturn x else : r eturn y printMax( 3 , 5 )

Modules
Any python file is considered a module
Modules can be imported or run by themselves
if __name__ == '__main__' : print ( 'This program is being run by itself' ) else : print ( 'I am being imported from another module' )

Modules #!/usr/bin/python # Filename: mymodule_demo.py import mymodule mymodule.sayhi() print ( 'Version' , mymodule.__version__) #!/usr/bin/python # Filename: mymodule.py def sayhi (): print ( 'Hi, this is mymodule speaking.' ) __version__ = '0.1' # End of mymodule.py

OOP class MyClass : """This is a docstring.""" name = "Eric" def say (self): return ( 'My name is {0}' .format(name)) instance = MyClass() print instance.say()

OOP class Person : def __init__ (self, name): self.name = name def __del__ (self): print ( 'deleting this person' ,self.name) def sayHi (self): print ( 'Hello, my name is' , self.name) p = Person( 'Swaroop' ) p.sayHi() del p

OOP
All class members (including the data members) are public and all the methods are virtual in Python.
Double undersocre prefix turns them private
e.g.: __privatevar,
Inheritance
MetaClasses
class SchoolMember (metaclass=ABCMeta): @abstractmethod def tell (self): pass
class Teacher (SchoolMember):

Input & Output #input something = input( 'Enter text: ' ) #output print (something)

Files myString = ”This is a test string” f = open( 'test.txt' , 'w' ) # open for 'w'riting f.write(myString) # write text to file f.close() # close the file f = open( 'test.txt' ) #read mode while True : line = f.readline() if len(line) == 0 : # Zero length indicates EOF break print (line, end= '' ) f.close() # close the file

Pickle import pickle shoplistfile = 'shoplist.data' shoplist = [ 'apple' , 'mango' , 'carrot' ] f = open(shoplistfile, 'wb' ) pickle.dump(shoplist, f) # dump the object to a file f.close() del shoplist # destroy the shoplist variable f = open(shoplistfile, 'rb' ) storedlist = pickle.load(f) # load the object from the file print (storedlist)

More …
Exception Handling
Standard Library
Passing Tuples
Logging Module

Linux and Python
What is Python ???
Why Python ???
Syntax Walkthroughs
Linux and Python

Linux and Python
Installed by default in most distros
Various editors
Text editors, IDLE , plugins for eclipse & Netbeans
Embeddable in many applications as scripting interface
Rhythmbox, Blender, OpenOffice, BitTorrent, ...

Linux and Python ” Talk is cheap. Show me the code.” Linus Torvalds

Demos
Backup Script
Simple XML Processing
Simple Spell Checker
Python Virus
Open Office Script
Rhythmbox python console
Basic Twitter client

Open Office macro script for python syntax Highlighing Demo #!usr/bin/python #Send a new Tweet from getpass import getpass import tweepy username = raw_input( 'Twitter username: ' ) password = getpass( 'Twitter password: ' ) basic_auth = tweepy.BasicAuthHandler(username, password) api = tweepy.API(basic_auth) api.update_status( "Hello Twitter !!! I'm a Pythoneer" )

More Resources
http://wiki.python.org/moin/BeginnersGuide
http://www.python.org/doc/faq/
Learn Python in 10 minutes: http://www.poromenos.org/tutorials/python
Byte of Python: http://www.swaroopch.com/notes/Python
Dive Into Python: http://diveintopython.org/
Google

Any Questions ???

Thank You

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Programming Under Linux In Python

by Marwan Osman

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