Python-Chapter2 (1)

Chapter 2: Elementary Programming

Writing a Simple Program

• Example Task: Write a program to compute the area of a circle.

  • Steps:

    1. Get the circle’s radius from the user.

    2. Compute area using the formula: area = radius * radius * π

    3. Display the result.

• Sample Code (ComputeArea.py):

  radius = 20  # Assign a value to radius
  area = radius * radius * 3.14159  # Compute area
  print("The area for the circle of radius", radius, "is", area)  # Display results

• Tip: Always outline your program as an algorithm before starting to code.

Reading Input from the Console

• Input Method: Use input() function to read user input:

  variable = input("Enter a value:")  # Input as string

• Evaluating Input: Use eval() to convert to a numeric value.

  • Examples:

    • eval("34.5") returns 34.5.

    • eval("345") returns 345.

    • eval("3 + 4") returns 7.

• Links: eval Function | input Function

Handling Console Input for Area Calculation

• Sample Code (ComputeAreaWithConsoleInput.py):

  radius = eval(input("Enter a value for radius:"))
  area = radius * radius * 3.14159  # Compute area
  print("The area for the circle of radius", radius, "is", area)

Identifiers

• Definition: Identifiers are names for elements like variables and functions.

• Examples: radius, area, input, eval, print

• Rules:

  • Must start with a letter or underscore.

  • Cannot be a keyword (e.g., import).

  • Can be of any length.

Variables, Assignment Statements, and Expressions

• Variables: Reference values that can change.

• Assignment Operator: = is used to assign values.

• Syntax: variable = expression

  • Example assignments:

    • y = 1

    • radius = 1.0

    • x = 5 * (3 / 2) + 3 * 2

• Multiple Variable Assignment: i = j = k = 1

Scope of Variables

• Definition: The part of the program where the variable can be used.

• Caution: A variable must be created before use to avoid references to uninitialized variables.

Simultaneous Assignments

• Syntax: var1, var2, ..., varn = exp1, exp2, ..., expn

• Example:

  x, y = 1, 2
  x, y = y, x  # Swap values

Named Constants

• Definition: Identifiers representing permanent values used in a program.

• Benefits:

  1. Reduces repeated typing of the same value.

  2. Easier to update values in one place.

  3. Improves code readability.

Numeric Data Types and Operators

• Types: Integers and floating-point numbers.

• Operators: Used with numeric types: +, -, *, /, //, **, %.

• Example: 1.0 is float; 1 is integer.

Display Time Example

• Sample Code (DisplayTime.py):

  seconds = eval(input("Enter an integer for seconds:"))
  minutes = seconds // 60
  remainingSeconds = seconds % 60
  print(seconds, "seconds is", minutes, "minutes and", remainingSeconds, "seconds")

Scientific Notation

• Format: Can be represented as a x 10^b. Examples:

  • 1.23456E2 = 123.456

  • 1.23456E-2 = 0.0123456

• Caution: Use of numbers beyond memory capacity can lead to overflow errors.

Evaluating Expressions and Operator Precedence

• Order of Operations:

  1. Exponentiation (**)

  2. Multiplication, Float Division, Integer Division, Remainder

  3. Addition and Subtraction

Augmented Assignment Operators

• Overview: Combine arithmetic operators with assignment.

  • Operators: +=, -=, *=, /=, //=, %=, **=.

Type Conversions and Rounding

• Rules: If an operand is a float, the result is a float. Integers convert to float during operations.

• Conversion Example: int(value) for integer part.

• Rounding Example: round(value) to round to the nearest whole number.

Programming Exercises

1. Write a program to compute gratuity based on subtotal and gratuity rate.

   • Example: Enter subtotal (10), gratuity rate (15%).

   • Output: Gratuity (1.5), Total (11.5).

2. Write a program to sum digits of an integer.

   • Example: Input (932), Output: Sum (14).

3. Calculate Body Mass Index (BMI) based on weight and height.

   • Conversion: 1 pound = 0.45359237 kg, 1 inch = 0.0254 m.