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Python An Introduction

Arulalan.T

arulalant@gmail.com

Centre for Atmospheric Sciences

Indian Institute of Technology Delhi

mailto:arulalant@gmail.commailto:arulalant@gmail.com

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Python is a Programming Language

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There areso many

Programming Languages.

Why Python?

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Python is simple and beautiful

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Python is Easy to Learn

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Python is Free Open Source Software

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Can Do

Text Handling

System Administration

GUI programming Web Applications

Database Apps

Scientific Applications

Games

NLP

...

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H i s t o r y

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Guido van Rossum

Father of Python1991

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Perl Java Python Ruby PHP1987 1991 1993 1995

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What is

Python?

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Python is...

A dynamic,open source

programming language with a focus on

simplicity and productivity. It has an

elegant syntax that is natural to

read and easy to write.

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Quick and Easy

Intrepreted Scripting Language

Variable declarations are unnecessary

Variables are not typed

Syntax is simple and consistent

Memory management is automatic

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Object Oriented Programming

Classes

Methods

Inheritance

Modules

etc.,

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Examples!

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print Hello World

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No Semicolons !

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Indentation

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You have to follow

the Indentation

Correctly.

Otherwise,

Python will beat

you !

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Discipline

Makes

Good

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Variables

colored_index_cards

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No Need to Declare Variable Types !

Python Knows Everything !

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value = 10

print value

value = 100.50

print value

value = This is String

print value * 3

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Input

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name = raw_input(What is Your name?)

print "Hello" , name , "Welcome"

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Flow

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if score >= 5000 :print You win!

elif score

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Loop

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for i in range(1, 5):

print i

else:print 'The for loop is over'

b

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number = 23

while True :

guess = int(raw_input('Enter an integer : '))

if guess == number :

print 'Congratulations, you guessed it.'

running = Falseelif guess < number :

print 'No, it is a little higher than that.'

else:

print 'No, it is a little lower than that.'

print 'Done'

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Array

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List = Array

numbers = [ "zero", "one", "two", "three",

"FOUR" ]

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List = Array

numbers = [ "zero", "one", "two", "three","FOUR" ]

numbers[0]>>> zero

numbers[4] numbers[ 1]

>>> FOUR >>> FOUR

numbers[ 2]

>>> three

Multi Dimension List

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Multi Dimension List

numbers = [ ["zero", "one"],["two", "three","FOUR" ]]

numbers[0]>>> ["zero", "one"]

numbers[0][0] numbers[ 1][ 1]

>>> zero >>> FOUR

len(numbers)

>>> 2

S Li

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Sort List

primes = [ 11, 5, 7, 2, 13, 3 ]

S t Li t

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Sort List

primes = [ 11, 5, 7, 2, 13, 3 ]

primes.sort()

S t Li t

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Sort List

primes = [ 11, 5, 7, 2, 13, 3 ]

primes.sort()

>>> [2, 3, 5, 7, 11, 13]

S t Li t

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Sort List

names = [ "Shrini", "Bala", "Suresh","Arul"]

names.sort()

>>> ["Arul", "Bala","Shrini","Suresh"]

names.reverse()

>>> ["Suresh","Shrini","Bala","Arul"]

Mi d Li t

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Mixed List

names = [ "Shrini", 10, "Arul", 75.54]

names[1]+10

>>> 20

names[2].upper()

>>> ARUL

Mixed List

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Mixed List

names = [ "Shrini", 10, "Arul", 75.54]

names[1]+10

>>> 20

names[2].upper()

>>> ARUL

Append on List

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Append on List

numbers = [ 1,3,5,7]

numbers.append(9)

>>> [1,3,5,7,9]

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Tuplesimmutable

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names = ('Arul','Dhastha','Raj')

name.append('Selva')

Error : Can not modify the tuple

Tuple is immutable type

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String

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name = 'Arul'

name[0]

>>>'A'

myname = 'Arul' + 'alan'>>> 'Arulalan'

split

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name = 'This is python string'

name.split(' ')

>>>['This','is','python','string']

comma = 'Shrini,Arul,Suresh'

comma.split(',')

>>> ['Shrini','Arul','Suresh']

join

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li = ['a','b','c','d']

s = ' '

new = s.join(li)

>>> a b c d

new.split(' ')>>>['a','b','c','d']

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'small'.upper()

>>>'SMALL'

'BIG'.lower()

>>> 'big'

'mIxEd'.swapcase()>>>'MiXwD'

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{

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menu = {idly : 2.50,

dosai : 10.00,coffee : 5.00,ice_cream : 5.00,

100 : Hundred}

menu[idly]

2.50

menu[100]Hundred

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Function

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def sayHello():

print 'Hello World!' # block belonging of fn

# End of function

sayHello() # call the function

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def printMax(a, b):if a > b:

print a, 'is maximum'

else: print b, 'is maximum'

printMax(3, 4)

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Using in built Modules

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#!/usr/bin/python

# Filename: using_sys.py

import time

print 'The sleep started'

time.sleep(3)

print 'The sleep finished'

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#!/usr/bin/python

import os

os.listdir('/home/arulalan')

os.walk('/home/arulalan')

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Making Our Own Modules

#!/usr/bin/python

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#!/usr/bin/python

# Filename: mymodule.py

def sayhi():

print Hi, this is mymodule speaking.

version = '0.1'

# End of mymodule.py

#!/ /bi / th

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#!/usr/bin/python

# Filename: mymodule_demo.py

import mymodule

mymodule.sayhi()

print 'Version', mymodule.version

#!/usr/bin/python

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# Filename: mymodule_demo2.py

from mymodule import sayhi, version# Alternative:

# from mymodule import *

sayhi()

print 'Version', version

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Class

Classes

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class Person:

pass # An empty block

p = Person()

print p

Classes

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class Person:

def sayHi(self):

print 'Hello, how are you?'

p = Person()

p.sayHi()

Classes

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class Person:

def __init__(self, name):

#like contstructor

self.name = name

def sayHi(self):print 'Hello, my name is', self.name

p = Person('Arulalan.T')

p.sayHi()

Classes

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Inheritance

Classes

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class A:

def hello(self):

print ' I am super class '

class B(A):

def bye(self):print ' I am sub class '

p = B()

p.hello()

p.bye()

Classes

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class A:

Var = 10def __init__(self):

self.public = 100

self._protected_ = 'protected'self.__private__ = 'private'

Class B(A):

pass

p = B()

p.__protected__

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File Handling

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File Writing

poem = ''' Programming is fun

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When the work is done

if you wanna make your work also fun:use Python!

'''

f = file('poem.txt', 'w') # open for 'w'riting

f.write(poem) # write text to file

f.close()

File Reading

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f= file('poem.txt','r')for line in f.readlines():

print line

f.close()

Database Intergration

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import psycopg2

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conn = psycopg2.connect(" dbname='pg_database'user='dbuser'host='localhost'password='dbpass' ")

cur = conn.cursor()

cur.execute("""SELECT * from pg_table""")rows = cur.fetchall()

print rows

cur.close()

conn.close()

import psycopg2

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conn = psycopg2.connect(" dbname='pg_database'user='dbuser'host='localhost'password='dbpass' ")

cur = conn.cursor()

cur.execute("'insert into pg_table values(1,'python')"')conn.commit()

cur.close()

conn.close()

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THE END of code : )

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How to learn ?

Python Shell

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Interactive Python

Instance Responce

Learn as you type

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bpython

ipython

}

teach you very easily

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Python can communicate

With

OtherLanguages

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C+

Python

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Java+

Python

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GUI

With

Python

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Glade

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Glade

+

Python

+GTK

=

GUI APP

GLADE

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Using Glade + Python

Web

Web

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Web Frame Work in Python

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