Introduction to Python

Python is a widely used high-level programming language created by Guido van Rossum and first released in 1991.

Identifiers

A Python identifier is a name used to identify a variable, function, class, module or other objects.

An identifier starts with a letter (A - Z or a - z) or an underscore (_) followed by zero or more letters, underscores and digits (0 to 9).

var1 = 1

var2 = 10

Keywords 

These are reserved words and you cannot use them as constant or variable or any other identifier names. All the Python keywords contain lowercase letters only.

Examples - 

print, and , exec, for, if etc.

Hello World! 

Lets use the print keyword to print "Hello World!"

print "Hello World!"

Declaring variables

Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory.

var1 = 1
var2 = 10

name = "John"

Standard Data Types 

Python has five standard data types −

• Numbers

• String : identified using quotation marks

• List : items separated by commas enclosed in brackets. Size can be changed.

• Tuple : similar to list enclosed in parentheses. Size cannot be further updated.

• Dictionary

  dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}

Decision Making

Odd or Even

Check if the number is odd or even

Loops

• While 
• For
• Do while

Print number 1 - 100

Use loops to print numbers from 1 - 100

Fahrenheit to Celsius

Convert Fahrenheit to Celsius

 ​C = (F- 32) / 1.8​

Can you convert Celsius to Fahrenheit?

Lists

In Python list can be written as a list of comma-separated values (items) between square brackets

list1 = ['physics', 'chemistry', 1997, 2000];
list2 = [1, 2, 3, 4, 5, 6, 7 ];

print "list1[0]: ", list1[0]
print "list2[1:5]: ", list2[1:5]

Tuples

A tuple is a sequence of immutable Python objects.

#!/usr/bin/python

tup1 = ('physics', 'chemistry', 1997, 2000);
tup2 = (1, 2, 3, 4, 5, 6, 7 );

print "tup1[0]: ", tup1[0]
print "tup2[1:5]: ", tup2[1:5]

Dictionary

Each key is separated from its value by a colon (:), the items are separated by commas, and the whole thing is enclosed in curly braces.

#!/usr/bin/python

dict = {'Name': 'Zara', 'Age': 7, 'Class': 'First'}

print "dict['Name']: ", dict['Name']
print "dict['Age']: ", dict['Age']

Open a file

file = open('filename', 'r')

Largest number in a file

Find the largest number from a text file

Functions

A function is a block of organized, reusable code that is used to perform a single, related action.

def printme( str ):
   "This prints a passed string into this function"
   print str
   return

def functionname( parameters ):
   "function_docstring"
   function_suite
   return [expression]

Example -