Introduction to Python

What is a Program?

• A computer program comprises instructions to perform a specific task when executed by a computer
• Computer programs get written in a programming language

What is Python?

• Python is a high-level, interpreted, interactive, object-oriented scripting language
• Python is designed for high readability
• Python is used in web applications, software development, data science, and machine learning (ML)
• Guido van Rossum created Python
• Python was released in 1991

Features of Python

• Python is open source
• Python is beginner-friendly
• Python is an interpreted language
• Python is interactive
• Python is portable
• Python is object-oriented

What Python Can Do

• When Python is installed, an IDE called IDLE also gets installed
• IDLE (GUI integrated) facilitates running Python
• IDLE is the standard, popular Python development environment
• IDLE is an acronym for Integrated Development Environment
• IDLE enables editing, running, browsing, and debugging Python Programs using one interface
• The Python shell can be used in interactive mode and script mode
• Interactive mode allows interaction with the OS
• Script mode lets users create and edit Python source files

Downloading and Installing Python for Windows

• The Windows Python interpreter is available for free download
• The website is https://www.python.org/downloads/
• After downloading the installer, run it
• After installation, Python 3.7 can be found in the start menu

Starting Python

• On Windows, open the Start menu, select All Programs, Python 3.7, and then IDLE (Python 3.7 32 bit)
• A window with the >>> prompt indicates the interactive shell
• Python statements get executed one by one in this window
• This is preferable when you want to see the output of each line of code

Print Function

• Functions print a specified message to the screen or standard output device
• The message is a string or any other object (converted to a string before printing)
• To print "Hello World" use: >>>print("Hello World!")
• You can print multiple objects: >>>print("Hello,", "How Are You?")

Try it Yourself

• Practice by finding the average of three marks using (75+85+65)/3
• Find the area of a circle with radius 5 using 22/7 * 5 * 5
• Combine strings "RAVI" and "Kant" using the + operator
• Multiply the string "###" by 3

Exiting Python

• To exit, use these commands: quit(), exit(), or Ctrl+D

Writing Python Programs

• Write instructions into the file editor to create an entire Python program
• The file editor, accessible via File -> New File in IDLE, offers features for coding

Python Operators

• Operators are symbols for computations applied to operands (values or variables)
• Operators have different behaviors based on the data type
• Applying operators to operands forms an expression
• Operators are categorized as Arithmetic, Relational, Logical, or Assignment
• Values and variables used with an operator are called operands

Arithmetic Operators

• Perform mathematical operations like addition, subtraction, multiplication, etc.
• Addition: +
• Subtraction: -
• Multiplication: *
• Division: /
• Integer Division: //
• Remainder: %
• Raised to power: **

Comparison Operators

• Comparison operators compare two values/variables and return True or False (boolean result)
• > Greater Than, < Less Than, == Equal To, != Not Equal to , >= Greater than or Equal to, <= Less than or equal to

Logical Operators

• Combine and manipulate Boolean values (True or False)
• and: Returns True if both operands are True
• or: Returns True if at least one operand is True
• not: Returns the opposite of the operand's Boolean value

Variables and Data Types

• Identifiers name entities like classes, functions, and variables, differentiating them

Datatypes

• Every value in Python has a datatype
• Everything is an object; data types are classes, and variables are instances of these classes

Python Comments

• Comments are text that doesn't affect code output; they explain the program

Single-Line Comments

• Single line comments in Python start with # (hash sign)

Multi-Line Comments

• Multi-line comments use triple single quotes (''') at the beginning and end

Input Function

• Displays a string message to prompt user input
• Program flow pauses until the user enters input and presses return

Difference Between == and = Operators

• == is a relational operator that checks if the values on both sides are equal
• = is an assignment operator that assigns the value on the right to the variable on the left

Conditional Statements / Control Statements

• Control the program flow based on conditions, executing different code blocks depending on whether a condition evaluates to True or False
• Flow control directs a program's path based on conditions; the outcome is True or False

If Statement

• The simplest decision-making statement
• If a condition is true, a statement or code block gets executed

If...Else Statements

• Executes code based on whether the condition is true (if block) or false (else block)
• Else statements consist of the keyword else, a colon, and an indented block of code

Learn about Python, a high-level, interpreted, object-oriented language created by Guido van Rossum and released in 1991. Python is open source, beginner-friendly, and used in web applications, software development, data science, and machine learning.