Objective

In this unit we introduce arithmetic and comparison operators in Python. You will understand how these operators work, how they can be used, and their role in creating more complex structures and logic in Python programs. By the end of this unit, you should be comfortable using these operators in various scenarios, including mathematical operations and comparison between different variables and values.

Arithmetic Operators

In Python, you can perform mathematical operations with arithmetic operators. The most common operators are:

• Addition +: Adds values on either side of the operator.
• Subtraction -: Subtracts the right-hand operand from the left-hand operand.
• Multiplication *: Multiplies values on either side of the operator.
• Division /: Divides the left-hand operand by the right-hand operand.
• Modulus %: Divides the left-hand operand by the right-hand operand and returns the remainder.
• Exponent **: Performs exponential calculation on operators.

Here's an example:

# Store some numbers in variables
a = 10
b = 2

# Use arithmetic operators
print(a + b)  # Output: 12
print(a - b)  # Output: 8
print(a * b)  # Output: 20
print(a / b)  # Output: 5.0
print(a % b)  # Output: 0
print(a ** b) # Output: 100

Comparison Operators

Comparison operators are used to compare values. The result of a comparison is a boolean value, either True or False. The most common comparison operators are:

• Equal to ==: If the values of two operands are equal, then the condition becomes true.
• Not equal to !=: If values of two operands are not equal, then condition becomes true.
• Greater than >: If the value of the left operand is greater than the value of the right operand, then the condition becomes true.
• Less than <: If the value of the left operand is less than the value of the right operand, then the condition becomes true.
• Greater than or equal to >=: If the value of the left operand is greater than or equal to the value of the right operand, then the condition becomes true.
• Less than or equal to <=: If the value of the left operand is less than or equal to the value of the right operand, then the condition becomes true.

Here's an example:

# Store some numbers in variables
x = 10
y = 20

# Use comparison operators
print(x == y)  # Output: False
print(x != y)  # Output: True
print(x > y)   # Output: False
print(x < y)   # Output: True
print(x >= y)  # Output: False
print(x <= y)  # Output: True

Project: Draw Different Shapes Based on User's Input

Now, let's apply our understanding of arithmetic and comparison operators in a project that interacts with the user. This program will draw different shapes based on the user's input.

import turtle

# Create a new turtle screen and set its background color
screen = turtle.Screen()
screen.bgcolor("white")

# Initialize a turtle object
t = turtle.Turtle()

# Ask the user for a number between 1 and 3
# Note: we're converting the result from the input() function
# to an integer using the int() function in a single step.
user_input = int(input("Enter a number between 1 and 3: "))

# Use the equality operator "==" to check if the value
# entered by the user is a 1, 2 or 3
if user_input == 1:  # Square
    for _ in range(4):
        t.forward(100)
        t.right(90)
elif user_input == 2:  # Triangle
    for _ in range(3):
        t.forward(100)
        t.right(120)
elif user_input == 3:  # Circle
    t.circle(50)

# Wait until the window is closed
turtle.done()

As we did in the previous project, we create a window and initialize a Turtle object. We then use the input() and int() functions to grab the user's input and convert it to an integer.

The user input is then evaluated in a series of if statements to determine if a 1, 2, or 3 was entered. Depending on the input value, a square, triangle or circle is drawn on the screen.

What happens if you enter a value less than 1 or greater than 3? It would be nice if the user were reminded of the options and give them another chance to enter the correct value. We'll explore how to accomplish just that in future lessons.

In the next unit, we'll dive into the if statement and how we can use it to effectively control the flow of statements that are executed in a Python program.