python-an-introduction

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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