What are Python's built-in data types?

Question

Accepted Answer

Python has a rich set of built-in types covering numbers, text, collections, and more. Knowing them — and which are **mutable** vs **immutable** — is fundamental.

## Numeric types

```python
x = 42          # int  — arbitrary precision (no overflow!)
y = 3.14        # float
z = 2 + 3j      # complex
b = True        # bool (a subclass of int: True == 1)
```

Note: Python `int` has **arbitrary precision** — it never overflows (unlike fixed-size ints in C/Java); `2 ** 1000` just works.

## Text and bytes

```python
s = "hello"     # str  — Unicode text (immutable)
data = b"bytes" # bytes — raw binary (immutable)
```

## Collection types

```python
lst = [1, 2, 3]            # list  — ordered, MUTABLE, allows duplicates
tup = (1, 2, 3)            # tuple — ordered, IMMUTABLE
d = {"a": 1, "b": 2}       # dict  — key→value, mutable, insertion-ordered
s = {1, 2, 3}              # set   — unordered, unique elements, mutable
fs = frozenset({1, 2})     # frozenset — immutable set
```

## The special None type

```python
result = None   # NoneType — represents "no value" (like null)
if result is None:   # always compare to None with `is`, not ==
    ...
```

## Checking types

```python
type(x)             # <class 'int'>
isinstance(x, int)  # True — the preferred check (handles subclasses)
```

## Mutable vs immutable summary

```text
Immutable: int, float, bool, str, tuple, frozenset, bytes, None
Mutable:   list, dict, set, bytearray
```

This distinction matters a lot — immutable objects can be dict keys and are safe to share; mutable ones can change unexpectedly if aliased.

## Why it matters

The built-in types are the vocabulary of all Python code.

Knowing each one's purpose (list for ordered sequences, dict for key-value, set for uniqueness, tuple for fixed records), the arbitrary-precision integers, and especially the **mutable-vs-immutable** split (which governs dict keys, aliasing bugs, and what can be safely shared) is foundational.

Choosing the right type for the job — and understanding its mutability — is a core Python skill that affects correctness and performance throughout a program.