Skip to main content

Expressions, Numbers, and Operations

This is the most fundamental page in the main Python track. The goal isn't to memorize every operator, but to build a few solid impressions first:

  • What are the common numeric types in Python
  • What + - * / // % ** actually do
  • Where it's easy to get the syntax right but the result wrong

Common Numeric Types​

a = 10       # int
b = 3.14     # float
c = 2 + 3j   # complex

In everyday development, you'll encounter int and float most often.

Basic Operators​

print(10 + 3)   # 13
print(10 - 3)   # 7
print(10 * 3)   # 30
print(10 / 3)   # 3.3333333333333335
print(10 // 3)  # 3
print(10 % 3)   # 1
print(10 ** 3)  # 1000

Three distinctions I remind myself of most often​

  • /: True division, result is usually a float
  • //: Floor division, keeps only the integer part of the quotient
  • %: Modulo (remainder)

Operator Precedence​

As in most languages, multiplication and division take priority over addition and subtraction; when in doubt, just add parentheses.

result = 2 + 3 * 4      # 14
result = (2 + 3) * 4    # 20

My own habit: whenever an expression gets even slightly long, I proactively add parentheses for clarity rather than betting on my memory of precedence rules.

Comparison and Logical Operators​

print(3 > 2)                   # True
print(3 == 2)                  # False
print(3 > 2 and 5 > 1)         # True
print(3 > 2 or 5 < 1)          # True
print(not (3 > 2))             # False

The easiest thing to mix up here:

  • = is assignment
  • == is the equality check

Common Built-in Math Functions​

print(abs(-10))          # 10
print(round(3.14159, 2)) # 3.14
print(pow(2, 5))         # 32
print(divmod(10, 3))     # (3, 1)

For basic math operations, built-in functions are more than enough; for more systematic math functions, see the math module.

Common items from the math module​

import math

print(math.sqrt(16))     # 4.0
print(math.floor(3.8))   # 3
print(math.ceil(3.2))    # 4
print(math.pi)           # 3.141592653589793

Don't idealize floating-point numbers​

It's easy for beginners to assume 0.1 + 0.2 should exactly equal 0.3, but floating-point numbers don't work that way:

print(0.1 + 0.2)         # 0.30000000000000004
print(0.1 + 0.2 == 0.3)  # False

A safer way to compare floats is to check whether the difference is small enough:

print(abs((0.1 + 0.2) - 0.3) < 1e-9)

A more practical way to think about it​

For this section, I prioritize remembering the following:

  • Distinguish /, //, % in numeric operations first
  • Add parentheses when expressions get longer
  • Don't use == for float comparisons
  • Think of abs(), round(), divmod(), and math first for common math tools