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Python – An Introduction
Shrinivasan T
tshrinivasan@gmail.com
http://goinggnu.wordpress.com

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
 System Administration
 GUI programming
 Web Applications
 Database Apps
 Scientific Applications
 Games
 NLP
 ...

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.,

You have to follow the
Indentation
Correctly.
Otherwise,
Python will beat you !

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 = input(“What is Your name?”)
print("Hello" ,name , "Welcome")

score=int(input(“ type a number”))
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)
print('The for loop is over')

number = 23
running = True
while running :
guess = int(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()
>>> print(primes)
[2, 3, 5, 7, 11, 13]

Sort List
names = [ "Shrini", "Bala", "Suresh",
"Arul"]
names.sort()
print(names)
>>> ["Arul", "Bala","Shrini","Suresh"]
names.reverse()
print(names)
>>> ["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'

name = 'This is python string'
name.split(' ')
>>>['This','is','python','string']
comma = 'Shrini,Arul,Suresh'
comma.split(',')
>>> ['Shrini','Arul','Suresh']
split

li = ['a','b','c','d']
s = '-'
new = s.join(li)
>>> a-b-c-d
new.split('-')
>>>['a','b','c','d']
join

'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
print(os.listdir('/home/arulalan'))
print(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)

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

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__
Classes

poem = ''' Programming is fun
When the work is done
if you wanna make your work also fun:
use Python!
'''
f = open('poem.txt', 'w') # open for 'w'riting
f.write(poem) # write text to file
f.close()

f= open('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

https://python.swaroopch.com/
Easiest free online book for
Python

Join ChennaiPy Mailing List and Ask/Answer questions
https://mail.python.org/mailman/listinfo/chennaipy

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