Python · Types: int, float, bool, None

Today’s topic was Python’s four basic scalar types.

• int: whole numbers. Python ints have arbitrary precision, so 2**100 just works and never overflows.
• float: double-precision floating point. Floats are binary approximations, so 0.1 + 0.2 is not exactly 0.3. Use math.isclose to compare them.
• bool: True and False. bool is a subclass of int, so True + True == 2.
• None: the single value of type NoneType. It means “no value”, and you test for it with is None.

/ always returns a float. // is floor division and % is the remainder. type() tells you what you have.

Truthiness: 0, 0.0, "", [], {} and None are all falsy. Most other values are truthy.

import math

print(2 ** 100)
print(7 / 2, 7 // 2, 7 % 2)
print(0.1 + 0.2, 0.1 + 0.2 == 0.3, math.isclose(0.1 + 0.2, 0.3))
print(True + True, isinstance(True, int))

result = None
print(result is None, type(result).__name__)
for v in [0, 1, "", "hi", [], None]:
    print(repr(v), "->", bool(v))

Output:

1267650600228229401496703205376
3.5 3 1
0.30000000000000004 False True
2 True
True NoneType
0 -> False
1 -> True
'' -> False
'hi' -> True
[] -> False
None -> False