Built-in types

This page enumerates every type that the interpreter defines and exposes through the builtins module or the runtime. For each, the public methods, the slots they fill, and any non-obvious rules.

Source-of-record: Objects/, Lib/, the standard type hierarchy.

Truth-value testing

Every type can be tested in a boolean context. The default rule:

Returns false
None, False
Zero of any numeric type: 0, 0.0, 0j, Decimal(0)
Empty containers: '', (), [], {}, set(), range(0)
Objects whose __bool__ returns False
Objects whose __len__ returns 0 (when __bool__ absent)

NoneType

Property	Value
Single instance	None
Truthy	No
Subclassable	No
__repr__	'None'

NotImplementedType

Property	Value
Single instance	NotImplemented
Returned from	Binary operators that decline to handle.
Truthy	Raises DeprecationWarning since 3.9.

EllipsisType

Property	Value
Single instance	Ellipsis (...)
Truthy	Yes

Numeric types

int

Arbitrary-precision integers. bool is a subclass.

Constructors

Form	Result
int()	0
int(x)	Truncate x (uses __int__ or __index__).
int("42")	Parse decimal.
int("ff", 16)	Parse with explicit base 2-36.
int("0xff", 0)	Infer base from prefix.

Methods

Method	Returns
bit_length()	Number of bits to represent abs(self).
bit_count()	Number of 1 bits (popcount).
to_bytes(length, byteorder, *, signed=False)	Big/little-endian byte string.
from_bytes(bytes, byteorder, *, signed=False)	Class method.
as_integer_ratio()	(self, 1).
is_integer()	Always True.
__floor__, __ceil__, __round__	Self.
__index__	Self.
numerator, denominator	self, 1.
real, imag	self, 0.
conjugate()	Self.

bool

Subclass of int. Singletons True == 1, False == 0.

Constructor	Result
bool()	False
bool(x)	True if x is truthy, else False.

bool cannot be subclassed.

float

IEEE 754 double.

Constructors

Form	Result
float()	0.0
float(x)	Numeric coerce.
float("1.5")	Parse text.
float("inf")	Positive infinity.
float("nan")	NaN.

Methods

Method	Returns
as_integer_ratio()	Exact (numerator, denominator).
is_integer()	True if integral.
hex()	Hex string representation.
fromhex(s)	Class method; inverse of hex.
__round__(ndigits=None)	Banker's rounding.
real, imag, conjugate()	Self, 0.0, self.

complex

Pair of double. Constructors: complex(), complex(real, imag=0), complex("1+2j").

Attribute / method	Returns
.real	Real part.
.imag	Imaginary part.
.conjugate()	Reflection over the real axis.

Iterator types

A type is an iterator if it implements __iter__ (returning self is conventional) and __next__. Calling __next__ returns the next value or raises StopIteration.

Iterator	Source
iter(seq)	Built-in.
iter(callable, sentinel)	Calls callable until it returns sentinel.
Generator	yield-containing function.
map, filter, zip	Lazy iterators over their arguments.
range_iterator	iter(range(...)).
enumerate, reversed	Built-ins.

Sequence types

Common operations (immutable)

Op	Returns
x in s, x not in s	bool
s + t	Concatenation.
s * n, n * s	Repetition.
s[i]	Element.
s[i:j], s[i:j:k]	Slice.
len(s)	Length.
min(s), max(s)	Extremes.
s.index(x[, i[, j]])	Index of first occurrence.
s.count(x)	Number of occurrences.

Common operations (mutable)

Op	Effect
s[i] = x	Assign element.
s[i:j] = t	Slice replacement.
del s[i], del s[i:j]	Delete.
s.append(x)	Append.
s.extend(t) / s += t	Extend.
s.insert(i, x)	Insert at index.
s.pop([i])	Remove and return.
s.remove(x)	Remove first occurrence.
s.reverse()	In-place reverse.
s.clear()	Empty.
s.copy()	Shallow copy.
s *= n	Repeat in place.

list

Mutable sequence of references. Resized geometrically. list.sort is stable Timsort:

Method	Effect
list.sort(*, key=None, reverse=False)	In-place sort.
list.copy()	Shallow copy.

tuple

Immutable fixed-size sequence. Methods are only .count and .index. Named tuples (collections.namedtuple, typing.NamedTuple) are subclasses adding named field access.

range

Lazy arithmetic progression range(start, stop, step). Hashable (__hash__ based on the produced sequence).

Property	Description
.start	Start value.
.stop	Exclusive endpoint.
.step	Step.

str

Sequence of Unicode code points. PEP 393 kinded storage: UCS-1, UCS-2, or UCS-4 depending on the maximum code point.

Methods (selected):

Method	Returns
capitalize, casefold, lower, upper, swapcase, title	Cased copy.
count, index, rindex, find, rfind	Substring search.
startswith, endswith	Prefix/suffix test.
lstrip, rstrip, strip	Strip whitespace or given chars.
center, ljust, rjust, zfill	Padding.
split, rsplit, splitlines	Split into list.
partition, rpartition	Three-way split at separator.
replace, translate, maketrans	Replacement.
join	Join an iterable of strings.
encode(encoding='utf-8', errors='strict')	Encode to bytes.
format, format_map	str.format machinery.
isalnum, isalpha, isascii, isdecimal, isdigit, isidentifier, islower, isnumeric, isprintable, isspace, istitle, isupper	Predicates.
removeprefix, removesuffix	Prefix/suffix removal.
expandtabs(tabsize=8)	Tab expansion.

bytes

Immutable byte sequence. Constructors: bytes(), bytes(int), bytes(iterable), bytes(string, encoding), bytes.fromhex(s).

Methods mirror str (decode, hex, split, replace, etc.) but operate on bytes. Element access yields int, not a length-1 bytes.

bytearray

Mutable counterpart of bytes. Adds append, extend, insert, pop, remove, reverse, clear, copy, +=, *=.

memoryview

View over a buffer-supporting object. Has .tobytes(), .tolist(), .cast(format[, shape]), .release(), plus attributes format, itemsize, ndim, shape, strides, readonly, c_contiguous, f_contiguous, contiguous, nbytes, obj.

Set types

set / frozenset

Operation	set	frozenset	Returns
len(s)	Y	Y	int
x in s	Y	Y	bool
s.isdisjoint(other)	Y	Y	bool
s.issubset(other) / <=	Y	Y	bool
s.issuperset(other) / >=	Y	Y	bool
s.union(*others) / |	Y	Y	new set
s.intersection(*others) / &	Y	Y	new set
s.difference(*others) / -	Y	Y	new set
s.symmetric_difference(o) / ^	Y	Y	new set
s.add(x)	Y	-	-
s.remove(x)	Y	-	-
s.discard(x)	Y	-	-
s.pop()	Y	-	element
s.clear()	Y	-	-
Augmented update |=, &=, -=, ^=	Y	-	self

Mapping types

dict

Insertion-ordered. Two internal layouts: combined (key+value contiguous) and split (keys shared between instances of the same type for __slots__-free classes).

Operation	Returns
len(d)	int
d[k]	value or __missing__ or KeyError
d[k] = v	-
del d[k]	-
k in d	bool
iter(d)	key iterator
d.copy()	shallow copy
d.clear()	-
d.get(k[, default])	value or default
d.setdefault(k[, default])	value, inserting default if absent
d.pop(k[, default])	value
d.popitem()	(k, v) LIFO
d.update(other) / d |= other	merge
d | other	new merged dict
d.keys(), d.values(), d.items()	view objects
dict.fromkeys(iter[, value])	classmethod

Dict views

d.keys(), d.values(), d.items() return view objects.

View	Implements
dict_keys	Set-like operations, iteration, length.
dict_values	Iteration, length. Not set-like.
dict_items	Set-like (when values are hashable), iteration, length.

Mutating the dict during view iteration raises RuntimeError.

mappingproxy

Read-only view of a dict. Used for class __dict__.

Function and method types

Type	Description
function	User-defined Python function.
method	Bound user method.
builtin_function_or_method	Built-in or C-level callable.
method-wrapper	Bound C-level slot method.
wrapper_descriptor	Unbound C-level slot method.
staticmethod	Descriptor: bypass self.
classmethod	Descriptor: bind to class.
functools.partial	Partial application.

Function attributes

Attribute	Meaning
__name__	Short name.
__qualname__	Qualified name.
__module__	Defining module.
__doc__	Docstring.
__code__	Code object.
__globals__	Globals dict.
__defaults__	Tuple of positional defaults.
__kwdefaults__	Dict of keyword-only defaults.
__closure__	Tuple of cell objects (or None).
__dict__	Attribute storage.
__annotations__	Annotation dict (lazy).
__type_params__	PEP 695 type params.
__wrapped__	Set by functools.wraps.

type metaobject

type is the default metaclass. Attributes:

Attribute	Meaning
type.__name__	Short name.
type.__bases__	Base classes.
type.__mro__	C3 linearisation.
type.__subclasses__()	Direct subclasses.
type.__instancecheck__	isinstance hook.
type.__subclasscheck__	issubclass hook.

type(name, bases, dict) constructs a new class dynamically.

Module type

A module object has:

Attribute	Meaning
__name__	Module name.
__doc__	Module docstring.
__file__	Source file (if any).
__loader__	Loader instance.
__spec__	ModuleSpec.
__package__	Package name.
__path__	Search path (packages only).
__dict__	Namespace.
__builtins__	Builtins reference.
__annotations__	Module-level annotations.

slice

slice(stop), slice(start, stop), slice(start, stop, step). Attributes: .start, .stop, .step. Method .indices(length) returns a tuple of three ints clamped to the sequence length.

Generic alias and union types

list[int] and friends create types.GenericAlias instances. They forward __call__ and __getattr__ to their origin. int | str creates a types.UnionType instance.

types module aliases

Name	Description
types.FunctionType	Same as function.
types.MethodType	Same as method.
types.GeneratorType	Generator object type.
types.CoroutineType	Coroutine object type.
types.AsyncGeneratorType	Async generator object type.
types.MappingProxyType	Read-only dict view.
types.SimpleNamespace	Attribute-based namespace.
types.ModuleType	Module type constructor.
types.TracebackType	Traceback object type.
types.FrameType	Frame object type.
types.CodeType	Code object type.
types.CellType	Closure cell type.

Gopy status

Type	State
All numeric, sequence, mapping, set types	Complete.
bytearray, memoryview	Complete.
Function / method types	Complete.
type and metaclass machinery	Complete.
slice, generic alias, union type	Complete.
Modules	Complete.
Buffer protocol	Complete for built-in types.

Reference

• CPython 3.14: Built-in types.
• objects/. gopy's per-type source.
• Data model.
• Special methods.