Operators and Expressions

Learn how to manipulate data using Python's powerful operators.

Arithmetic Operators

Perform mathematical operations:

a = 10
b = 3

# Addition
print(a + b)    # Output: 13

# Subtraction
print(a - b)    # Output: 7

# Multiplication
print(a * b)    # Output: 30

# Division (always returns float)
print(a / b)    # Output: 3.3333333333333335

# Floor Division (rounds down)
print(a // b)   # Output: 3

# Modulus (remainder)
print(a % b)    # Output: 1

# Exponentiation (power)
print(a ** b)   # Output: 1000 (10³)

Comparison Operators

Compare values and get boolean results:

x = 10
y = 5

print(x == y)   # False (equal to)
print(x != y)   # True (not equal to)
print(x > y)    # True (greater than)
print(x < y)    # False (less than)
print(x >= y)   # True (greater than or equal to)
print(x <= y)   # False (less than or equal to)

Comparing Strings

name1 = "Alice"
name2 = "Bob"

print(name1 == name2)    # False
print(name1 < name2)     # True (alphabetical order)

Logical Operators

Combine boolean expressions:

age = 25
has_license = True

# AND - both must be True
can_drive = age >= 18 and has_license
print(can_drive)  # True

# OR - at least one must be True
is_weekend = False
is_holiday = True
can_relax = is_weekend or is_holiday
print(can_relax)  # True

# NOT - inverts the boolean
is_raining = False
is_sunny = not is_raining
print(is_sunny)   # True

Practical Example

age = 16
has_license = True
has_insurance = True

# Check if person can legally drive
can_drive = age >= 18 and has_license and has_insurance
print(f"Can drive: {can_drive}")  # False (age requirement not met)

Assignment Operators

Update variable values efficiently:

# Basic assignment
x = 10

# Addition assignment
x += 5   # Same as: x = x + 5
print(x)  # 15

# Subtraction assignment
x -= 3   # Same as: x = x - 3
print(x)  # 12

# Multiplication assignment
x *= 2   # Same as: x = x * 2
print(x)  # 24

# Division assignment
x /= 4   # Same as: x = x / 4
print(x)  # 6.0

# Floor division assignment
x //= 2  # Same as: x = x // 2
print(x)  # 3.0

# Modulus assignment
x %= 2   # Same as: x = x % 2
print(x)  # 1.0

# Exponentiation assignment
x **= 3  # Same as: x = x ** 3
print(x)  # 1.0

Operator Precedence

Order in which operators are evaluated:

# Without parentheses
result = 2 + 3 * 4
print(result)  # 14 (multiplication first)

# With parentheses
result = (2 + 3) * 4
print(result)  # 20 (addition first)

# Complex expression
result = 10 + 5 * 2 ** 2 - 3
print(result)  # 10 + 5 * 4 - 3 = 10 + 20 - 3 = 27

Precedence Order (High to Low)

() - Parentheses
** - Exponentiation
*, /, //, % - Multiplication, Division, Floor Division, Modulus
+, - - Addition, Subtraction
<, <=, >, >=, ==, != - Comparisons
not - Logical NOT
and - Logical AND
or - Logical OR

Practical Examples

Example 1: Calculate Circle Area

PI = 3.14159
radius = 5

area = PI * radius ** 2
circumference = 2 * PI * radius

print(f"Area: {area:.2f}")
print(f"Circumference: {circumference:.2f}")

Example 2: Check Eligibility

age = 25
income = 50000
credit_score = 700

# Loan eligibility
eligible = (age >= 21 and age <= 65) and income >= 30000 and credit_score >= 650

print(f"Eligible for loan: {eligible}")

Example 3: Calculate Discount

price = 100
discount_percent = 20

discount_amount = price * (discount_percent / 100)
final_price = price - discount_amount

print(f"Original: ${price}")
print(f"Discount: ${discount_amount}")
print(f"Final: ${final_price}")

Common Mistakes

1. Forgetting Operator Precedence

# Wrong
result = 10 + 5 * 2  # Might expect 30, but gets 20

# Right
result = (10 + 5) * 2  # 30

2. Using = Instead of ==

# Wrong
x = 5
if x = 10:  # SyntaxError: assignment in condition
    print("x is 10")

# Right
if x == 10:
    print("x is 10")

3. Integer Division Surprise

# In Python 3
print(10 / 3)    # 3.333... (float division)
print(10 // 3)   # 3 (floor division)

Practice Exercises

Calculate the area and perimeter of various shapes
Write expressions to check multiple conditions
Use assignment operators to update a counter
Practice operator precedence with complex expressions
Build a simple calculator using operators

Next Lesson: String Operations and Formatting