Python Basics — Arithmetic Operators

Arithmetic Operators

Arithmetic operators perform mathematical calculations. Python supports all the standard math operations plus a few extras.

Operator Reference

Operator	Name	Example	Result
+	Addition	5 + 3	8
-	Subtraction	10 - 4	6
*	Multiplication	3 * 7	21
/	Division (true)	7 / 2	3.5
//	Floor division	7 // 2	3
%	Modulo (remainder)	7 % 3	1
**	Exponentiation	2 ** 10	1024

Addition and Subtraction

print(10 + 3)    # 13
print(10 - 3)    # 7
print(-5 + 3)    # -2
print(2.5 + 1.3) # 3.8

The + operator also works with strings (concatenation) and lists:

print("Hello" + " " + "World")  # Hello World
print([1, 2] + [3, 4])          # [1, 2, 3, 4]

Multiplication

print(4 * 5)     # 20
print(3 * 2.5)   # 7.5
print(-2 * 3)    # -6

The * operator also repeats strings and lists:

print("Ha" * 3)    # HaHaHa
print([0] * 5)     # [0, 0, 0, 0, 0]

Division: / vs //

Python has two division operators — understanding the difference is critical.

True Division (/)

Always returns a float, even when dividing two integers:

print(10 / 3)   # 3.3333333333333335
print(10 / 2)   # 5.0 (float, not int!)
print(7 / 2)    # 3.5

Floor Division (//)

Returns the result rounded down to the nearest integer:

print(10 // 3)   # 3
print(7 // 2)    # 3
print(10 // 2)   # 5

# With negative numbers — rounds toward negative infinity
print(-7 // 2)   # -4 (not -3!)
print(-10 // 3)  # -4

# Floor division with floats returns a float
print(7.0 // 2)   # 3.0
print(7 // 2.0)   # 3.0

Modulo Operator (%)

Returns the remainder after division:

print(10 % 3)    # 1 (10 ÷ 3 = 3 remainder 1)
print(15 % 5)    # 0 (15 ÷ 5 = 3 remainder 0)
print(7 % 2)     # 1

Common Use Cases

# Check if a number is even or odd
number = 42
if number % 2 == 0:
    print(f"{number} is even")  # 42 is even
else:
    print(f"{number} is odd")

# Check divisibility
if 15 % 3 == 0:
    print("15 is divisible by 3")  # 15 is divisible by 3

# Wrap around (clock arithmetic)
hours = 25
print(hours % 24)  # 1 (25 hours = 1 AM next day)

Exponentiation (**)

Raises a number to a power:

print(2 ** 3)     # 8 (2 × 2 × 2)
print(5 ** 2)     # 25 (5 × 5)
print(10 ** 0)    # 1 (anything to the power of 0)
print(2 ** 10)    # 1024

# Square root using **
print(25 ** 0.5)  # 5.0
print(27 ** (1/3)) # 3.0 (cube root)

Order of Operations (PEMDAS)

Python follows standard mathematical precedence:

Priority	Operator	Operation
1 (highest)	**	Exponentiation
2	+x, -x	Unary plus/minus
3	*, /, //, %	Multiplication, division, modulo
4 (lowest)	+, -	Addition, subtraction

# Without parentheses — follows PEMDAS
print(2 + 3 * 4)      # 14 (not 20)
print(2 ** 3 ** 2)     # 512 (3**2 = 9, then 2**9 = 512)
print(10 - 2 * 3 + 1)  # 5

# With parentheses — override precedence
print((2 + 3) * 4)     # 20
print((10 - 2) * (3 + 1))  # 32

Tip: When in doubt, use parentheses. They make your code clearer and prevent mistakes.

The divmod() Function

Returns both the quotient and remainder as a tuple:

quotient, remainder = divmod(17, 5)
print(f"17 ÷ 5 = {quotient} remainder {remainder}")
# 17 ÷ 5 = 3 remainder 2

# Useful for time conversions
total_minutes = 135
hours, minutes = divmod(total_minutes, 60)
print(f"{total_minutes} minutes = {hours}h {minutes}m")
# 135 minutes = 2h 15m

Common Mistakes

Mistake	Example	Fix
/ returns float	10 / 2 → 5.0	Use // for integer result
Negative floor division	-7 // 2 → -4	Rounds toward -∞, not zero
Division by zero	10 / 0 → ZeroDivisionError	Check divisor first
Operator precedence	2 + 3 * 4 → 14	Use parentheses: (2 + 3) * 4

Summary

• +, -, * work as expected for basic math
• / (true division) always returns a float
• // (floor division) rounds down to nearest integer
• % (modulo) returns the remainder — great for even/odd checks
• ** for exponentiation (powers and roots)
• Use parentheses to control order of operations
• Use divmod() when you need both quotient and remainder

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