Numbers

Python has three built-in numeric types: int for whole numbers of any size, float for decimals, and complex for complex numbers. It also offers the decimal and fractions modules when you need exact arithmetic.

Integers

small = 42
negative = -7
big = 2 ** 100
readable = 1_000_000

print(big)
print(readable)
print(0b1010, 0o17, 0xFF)

1267650600228229401496703205376
1000000
10 15 255

Python integers have no size limit — they grow as large as memory allows. That's unusual: most languages overflow at around 9 quintillion. Binary (0b), octal (0o) and hexadecimal (0x) literals are all ints.

Floats

pi = 3.14159
tiny = 1.5e-6
huge = 2e10

print(tiny, huge)
print(10 / 4)
print(10 / 5)
print(type(10 / 5))

1.5e-06 20000000000.0
2.5
2.0
<class 'float'>

Division with / always produces a float, even when the result is whole. Use // for integer (floor) division (lesson 12).

Floating-point precision

print(0.1 + 0.2)
print(0.1 + 0.2 == 0.3)
print(round(0.1 + 0.2, 2) == 0.3)

import math
print(math.isclose(0.1 + 0.2, 0.3))

0.30000000000000004
False
True
True

Floats are stored in binary, which can't represent most decimal fractions exactly — a limitation of computers in general, not Python. Compare floats with math.isclose(), round for display, and use Decimal (below) for money.

Useful built-in functions

print(abs(-12.5))
print(round(3.14159, 2))
print(round(2.5), round(3.5))
print(max(3, 9, 2), min(3, 9, 2))
print(sum([1.5, 2.5, 3]))
print(pow(2, 10), divmod(17, 5))

12.5
3.14
2 4
9 2
7.0
1024 (3, 2)

Note round(2.5) is 2: Python uses "banker's rounding", which rounds halves to the nearest even number to avoid bias in large calculations. divmod(a, b) returns the quotient and remainder together.

Number methods

print((3.75).is_integer(), (4.0).is_integer())
print((255).bit_length())
print((0.75).as_integer_ratio())
print(int(3.99), int(-3.99))

False True
8
(3, 4)
3 -3

int() truncates towards zero; for rounding down use math.floor, for up math.ceil (lesson 48).

Special float values

import math

inf = float("inf")
nan = float("nan")

print(inf > 10 ** 100, -inf < 0)
print(nan == nan, math.isnan(nan))
print(1 / 3)

True True
False True
0.3333333333333333

Unlike JavaScript, dividing by zero in Python raises an error instead of returning infinity: 1 / 0 raises ZeroDivisionError.

Exact arithmetic: Decimal and Fraction

from decimal import Decimal
from fractions import Fraction

print(Decimal("0.1") + Decimal("0.2"))
print(Decimal("19.99") * 3)
print(Fraction(1, 3) + Fraction(1, 6))

0.3
59.97
1/2

Decimal does base-10 arithmetic exactly, which is why financial software uses it. Always create decimals from strings — Decimal(0.1) would inherit the float's tiny error. Fraction keeps exact rational numbers.

Complex numbers

z = 3 + 4j
print(z.real, z.imag, abs(z))

3.0 4.0 5.0

You'll rarely need these outside engineering and science, but they're built in.

Try it yourself