Numbers

Big idea

Python has two everyday kinds of number: int for whole numbers and float for numbers with a decimal point.

The idea

apples = 12        # int
price = 0.45       # float
temp = -3          # int — negatives are fine

type() tells you what kind of value something is:

print(type(12))
print(type(0.45))
print(type(12.0))

output
<class 'int'>
<class 'float'>
<class 'float'>

12.0 is a float even though it's a whole number — the decimal point decides.

ints never overflow

In C an int has a maximum. A Python int just grows as big as it needs to:

print(2 ** 100)

output
1267650600228229401496703205376

(** means "to the power of" — more on operators soon.)

Division always gives a float

/ always gives a float, even when it divides exactly. For a whole-number answer, use //:

print(10 / 2)
print(7 / 2)
print(7 // 2)

5.0
3.5
3

Floats are close, not exact

A float stores its digits in binary, and most decimals (like 0.1) can't be written exactly in binary — the way 1/3 can't be written exactly in decimal. Tiny errors creep in:

print(0.1 + 0.2)
print(round(0.1 + 0.2, 2))

output
0.30000000000000004
0.3

That's not a Python bug; every language does it. round(x, 2) rounds to 2 decimal places when you need to show a tidy answer. For money, programmers often count in whole cents with ints.

Watch it

Handy number tools

• abs(-7) → 7 — distance from zero.
• round(3.14159, 2) → 3.14.
• max(3, 9, 4) → 9, min(3, 9, 4) → 3.
• Underscores make big numbers readable: 1_000_000 is one million.

total = 10
count = 4
print(total // count)

output
2.5

Think of it like

ints are counting on your fingers — always exact. floats are a measuring tape — great for lengths, but the last tiny fraction is always a little fuzzy.

Key terms

• int — A whole number, any size.
• float — A number with a decimal point; stored approximately.
• type() — Tells you the kind of a value.