Lesson1 python an introduction

Python – An Introduction
Arulalan.T
arulalant@gmail.com
Centre for Atmospheric Sciences
Indian Institute of Technology Delhi

Python is a Programming Language

There are so many
Programming Languages.

Why Python ?

Python is simple and beautiful

Python is Free Open Source Software

Can Do
● Text Handling ● Games
● System Administration ● NLP
● GUI programming
● Web Applications ● ...
● Database Apps
● Scientific Applications

Guido van Rossum
Father of Python
1991

Perl Java Python Ruby PHP
1987 1991 1993 1995

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.

Quick and Easy

Intrepreted Scripting Language

Variable declarations are unnecessary

Variables are not typed

Syntax is simple and consistent

Memory management is automatic

Object Oriented Programming

      Classes
         Methods

         Inheritance

         Modules

         etc.,

print “Hello World”

You have to follow
the Indentation
Correctly.

Otherwise,

Python will beat
you !

Discipline

Makes

Good

Variables

colored_index_cards

No Need to Declare Variable Types !

Python Knows Everything !

value = 10

print value

value = 100.50

print value

value = “This is String”

print value * 3

name = raw_input(“What is Your name?”)

print "Hello" , name , "Welcome"

if score >= 5000 :
print “You win!”
elif score <= 0 :
print “Game over.”
else:
print “Current score:”,score

print “Donen”

for  i   in   range(1, 5):
        print    i
else:
        print    'The for loop is over'

number = 23

while True :
        guess = int(raw_input('Enter an integer : '))
        if  guess == number :
                print 'Congratulations, you guessed it.'
                running = False
        elif  guess < number :
                print 'No, it is a little higher than that.'
        else:
                print 'No, it is a little lower than that.'

print  'Done'

List = Array

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

List = Array

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

numbers[0]
>>> zero

numbers[4]                                 numbers[1]
>>> FOUR                                  >>> FOUR
                         numbers[2]
          >>> three

Multi Dimension List

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

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

numbers[0][0]                       numbers[1][1]
>>> zero                                  >>> FOUR
                         len(numbers)
          >>> 2

Sort List

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

Sort List

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

primes.sort()

Sort List

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

primes.sort()

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

Sort List

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

names.sort()

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

names.reverse()

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

Mixed List

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

names[1]+10
>>> 20

names[2].upper()

>>> ARUL

Append on List

numbers = [ 1,3,5,7]

numbers.append(9)

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

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

name.append('Selva')

Error : Can not modify the tuple

Tuple is immutable type

name = 'Arul'

name[0]
>>>'A'

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

split
name = 'This is python string'

name.split(' ')
>>>['This','is','python','string']

comma = 'Shrini,Arul,Suresh'

comma.split(',')
>>> ['Shrini','Arul','Suresh']

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

new = s.join(li)
>>> abcd

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

'small'.upper()
>>>'SMALL'

'BIG'.lower()
>>> 'big'

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

menu = {
“idly” : 2.50,
“dosai” : 10.00,
“coffee” : 5.00,
“ice_cream” : 5.00,
100 : “Hundred”
}

menu[“idly”]
2.50

menu[100]
Hundred

def sayHello():
print 'Hello World!' # block belonging of fn
# End of function

sayHello() # call the function

def printMax(a, b):
        if a > b:
                print a, 'is maximum'
        else:
                print b, 'is maximum'
printMax(3, 4)

#!/usr/bin/python
# Filename: using_sys.py
import time

print 'The sleep started'
time.sleep(3)
print 'The sleep finished'

#!/usr/bin/python
import os

os.listdir('/home/arulalan')

os.walk('/home/arulalan')

#!/usr/bin/python
# Filename: mymodule.py
def sayhi():
print “Hi, this is mymodule speaking.”
version = '0.1'

# End of mymodule.py

#!/usr/bin/python
# Filename: mymodule_demo.py

import mymodule

mymodule.sayhi()
print 'Version', mymodule.version

#!/usr/bin/python
# Filename: mymodule_demo2.py
from mymodule import sayhi, version
# Alternative:
# from mymodule import *

sayhi()
print 'Version', version

Classes

class Person:
pass # An empty block

p = Person()

print p

Classes

class Person:
def sayHi(self):
print 'Hello, how are you?'

p = Person()

p.sayHi()

Classes
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

Inheritance

Classes
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
class A:
Var = 10
def __init__(self):
self.public = 100
self._protected_ = 'protected'
self.__private__ = 'private'

Class B(A):
pass
p = B()
p.__protected__

poem = ''' Programming is fun
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()

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

import psycopg2

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

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()

Python – Shell
Interactive Python

●

● Instance Responce
●
Learn as you type

bpython
ipython }
teach you very easily

Python can communicate
                 With
                Other
            Languages

Glade
                    +
                Python
                    +
                 GTK
                    =
             GUI APP

Lesson1 python an introduction

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