Basic Data Types

Every value in Python has a type, even though you never declare it explicitly. Knowing the core built-in types — and their quirks — is the foundation everything else in the language builds on.

Numbers: int and float

whole = 10        # int
decimal = 3.14    # float

int handles whole numbers with no size limit (Python automatically switches to arbitrary-precision arithmetic, so you'll never hit an integer overflow). float handles decimals, using the same 64-bit floating-point representation most languages use — which means the classic floating-point rounding quirk applies here too:

print(0.1 + 0.2)  # 0.30000000000000004

This isn't a Python bug; it's how binary floating-point math works everywhere. For money or anything requiring exact decimal precision, use the decimal module instead of raw floats.

Strings

greeting = "Hello"
name = 'Ada'
multiline = """This spans
multiple lines"""

Single and double quotes work identically — pick one and be consistent, or use double quotes when the string itself contains an apostrophe. Triple quotes (""" or ''') create multi-line strings, commonly used for docstrings (documentation attached to functions and classes, covered later).

Booleans

is_ready = True
is_done = False

True and False are capitalized in Python — unlike JavaScript's true/false. Booleans are technically a subtype of integers (True == 1 and False == 0 both evaluate to True), a quirk that rarely matters but occasionally explains surprising behavior.

None

None represents the deliberate absence of a value — Python's equivalent of null:

result = None

A function with no explicit return statement returns None automatically. Always compare against it with is None, not == None:

if result is None:
    print("Nothing here yet")

is checks that two names point to the exact same object, which matters because None is a true singleton — there's only ever one None in a running Python program.

Checking a value's type

print(type(42))        # <class 'int'>
print(type("hi"))      # <class 'str'>
print(type(3.14))      # <class 'float'>

type() returns a value's exact type, useful for debugging when a variable doesn't behave the way you expect. The next lesson covers converting between these types deliberately, and the one after that covers formatting them into readable strings.