Expressions, Operators, and User Input in Python

Statements

• Statement: A unit of code the Python interpreter can execute.
• Types of statements:
  • Print statement
  • Assignment statement
• Interactive mode: Typing and executing statements directly in the Python interpreter.
• Script mode: Writing a sequence of statements in a file and executing the script.

Example in Interactive Mode

• Assignment Statement: x = 5
  • Stores 5 in the memory allocated for x.
  • Typing x will display 5.
• Arithmetic Operation: x + y
  • Fetches values of x and y, adds them, and prints the result in interactive mode.
  • In a script, use print(x + y) to display the result.

Writing and Executing a Python Script

• Editor: Use any editor (e.g., vi editor in Linux).
• File Extension: .py for Python scripts.
• Example Script: first.py

  print(100)
  x = 5
  y = 20
  print(x + y)
  

• Execution: python3 first.py
  • Output: 100 25

Operators and Operands

• Operator: Special symbols that represent computations (e.g., +, -, *, /, **).
• Operand: Values the operator is applied to.
• Types of operators:
  • + (Addition)
  • - (Subtraction)
  • * (Multiplication)
  • / (Division)
  • ** (Exponentiation)

Division Operator Changes

• Python 2.x: Integer division (e.g., 7 / 5 results in 1).
• Python 3.x: Floating-point division (e.g., 7 / 5 results in 1.4).

Expressions

• Expression: Combination of values, variables, and operators.
• Examples:
  • 20 + 32
  • r - 1
  • 1 + 1
• Interactive Mode: Evaluates and displays the result.
• Script Mode: Use print to display results.

Order of Operations (PEMDAS)

• P: Parentheses
• E: Exponents
• MD: Multiplication and Division (same precedence)
• AS: Addition and Subtraction (same precedence)
• Left to Right: Operators with the same precedence are evaluated from left to right.

Modulus Operator

• Modulus: %
  • Yields the remainder when the first operand is divided by the second.
  • Example: 7 % 3 results in 1.
• Floor Division: //
  • Example: 7 // 5 results in 1.
• Usage: Extracts rightmost digits from a number.

String Operations

• Concatenation: + operator joins two strings.
  • Example: `