OIM3640 - Problem Solving and Software Design

2025 Spring

Session 08 (2/13)

Today's Agenda

• Welcome/News/Announcements
• Review
  • Exercises
  • Quiz 0
• Lecture - Iterations

Welcome/News/Announcements

• Quiz Policy
  • Quiz 0 counts as one exercise.
  • There are no make-up opportunities for unexcused absences.
  • The lowest grade will be dropped automatically, including any missed quiz.

• Communications
  • Meet with me in person during office hours at least once this semester.
  • Email - specify course # in subject title, e.g., "OIM3640: GitHub settings"
  • Use Slack/GitHub when asking code-related questions
• Questions?

What we have learned so far...

• Variables, expressions, statements
• Types: int, float, string, boolean, Nonetype, other data structures
• Functions
• turtle module
• Pseudo-code
• Conditional Statements
  • if...elif...else
  • recursion (not recommended for beginners)

Quick Quiz

1. What are the two main purposes of functions in programming?
2. If score is 95, what will be printed?

    if score >= 60:
        print("Pass")
    elif score >= 90:
        print("A")
    else:
        print("Fail")
   

3. Do the two function calls below have the same effect?

   def polygon(t, n, length):
       ...
   
   polygon(leo, 7, 70)
   polygon(leo, length=70, n=7)
   

Python Tips

1. __main__ check

   if __name__ == '__main__':
   # Running as the main program ...
   # but does not execute if loaded with import ...
   

   • Why: You should put this in all your Python scripts (YouTube)
2. To swap two variables:
   1. Use a temporary variable (in other programming languages)
   2. A more Pythonic way: x, y = y, x
3. Use comparison chain:

   # if bmi >= 18.5 and bmi <= 30:
   if 18.5 <= bmi <= 30:
   

Exercises

• Please check your OIM3640/Issues on GitHub.
  • Reply if we need to continue the conversation.
  • Reply (with evidence) and Close if you think it is fixed.
  • If you have any question regarding
    • class demo code, create new issue in OIM3640/oim3640
    • class material, create new issue in OIM3640/resources
• Suggestions / Requirements:
  • File/folder names - lowercase and underscore, eg. session04/type_demo.py
  • Please add docstrings for the functions your create!
  • Please test your functions!
  • Please use separate files for different questions.

Issues #0

def check_fermat(a, b, c, n):
    """"Checks Fermat's Last Theorem and prints the result."""
    if n > 2 and a**n + b**n == c**n:
        print("Holy smokes, Fermat was wrong!")
    else:
        print("No, that doesn't work.")


def check_number():
    """Gets inputs and calls check_fermat function"""
    a = int(input("Select value of a: "))
    ...
    return check_fermat(a, b, c, n)

• No need to add return in the second function

Issues #1

def get_bmi_category(BMI):
    """"""
    if BMI < 18.5:
        print("Underweight")
    elif 18.5 <= BMI < 24.9:
        print("Normal weight")
    elif 25 <= BMI < 29.9:
        print("Overweight")
    elif BMI > 30:
        print("Obesity")

• What if BMI is 29.95?

Issues #2

def calculate_bmi(height, weight):
    """Calculate bmi through input of your height and weight."""
    height = float(input("Your height in meters: "))
    weight = float(input("Your weight in kilograms: "))
    print("Your bmi is: ", round(weight / (height * height), 2))

calculate_bmi(1.70, 70)

• When calling the calculate_bmi function, the height and weight values are provided as arguments.
• Inside the function, the parameter variables - height and weight - should be treated as given, and should not be reassigned (unless absolutely necessary.)

Issues #3

def get_bmi_catagory(bmi):
    bmi = float(bmi)
    if bmi <= 18.5:
        print('Underweight')
    elif bmi in range[18.5, 25]:
        print('Normal weight')
    elif bmi in range[25, 30]:
        print('Overweight')
    else:
        print('Obesity')

• It's incorrect to use range in this context.
  • range is a function used to generate a sequence of numbers, commonly used in for loops.
  • range is not designed for checking if a value is within a range.

Issues #4

    ...
    if bmi < 18.5:
        print("Underweight")
    else:
        if bmi >= 18.5 and bmi < 25:
            print("Normal Weight")
        else:
            if bmi >= 25 and bmi < 30:
                print("Overweight")
            else:
                print("Obesity")

• Avoid excessive nesting of if ... else statements.

Issues #5

def get_bmi_category():
    weight = float(input("Input weight"))
    height = float(input("Input height in inches"))
    if calculate_bmi(weight, height) < 18.5:
        print("Underweight")
    elif calculate_bmi(weight, height) >= 18.5 and calculate_bmi(weight, height) < 25:
        print("Normal weight")
    elif calculate_bmi(weight, height) >= 25 and calculate_bmi(weight, height) < 30:
        print("Overweight")
    elif calculate_bmi(weight, height) >= 30:
        print("Obese")

• Function calculate_bmi(weight, height) might be executed 6 times in worst case, which is not ideal if
  • the function costs a lot of time/computing,
  • or the function has some other side effects.

Issues #6

def calculate_bmi(weight, height):
    bmi = 703 * (weight/height**2)
    if bmi <= 18.5:
        return "You are underweight"
    elif bmi > 18.5 and bmi <= 25:
        return "You are normal weight"
    elif bmi > 25 and bmi <= 29.9:
        return "You are overweight"
    else:
        return "You are obese!"

def start_bmi(weight, height):
    response = calculate_bmi(weight, height)
    return response

• start_bmi has no added value.
• calculate_bmi only needs to calculate and return bmi instead of doing everything in one place.

Session 08

• Iterations