optype

Building blocks for precise & flexible type hints.

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Installation

Optype is available as optype on PyPI:

pip install optype

For optional NumPy support, it is recommended to use the numpy extra. This ensures that the installed numpy version is compatible with optype, following NEP 29 and SPEC 0.

pip install "optype[numpy]"

See the optype.numpy docs for more info.

Example

Let's say you're writing a twice(x) function, that evaluates 2 * x. Implementing it is trivial, but what about the type annotations?

Because twice(2) == 4, twice(3.14) == 6.28 and twice('I') = 'II', it might seem like a good idea to type it as twice[T](x: T) -> T: .... However, that wouldn't include cases such as twice(True) == 2 or twice((42, True)) == (42, True, 42, True), where the input- and output types differ. Moreover, twice should accept any type with a custom __rmul__ method that accepts 2 as argument.

This is where optype comes in handy, which has single-method protocols for all the builtin special methods. For twice, we can use optype.CanRMul[T, R], which, as the name suggests, is a protocol with (only) the def __rmul__(self, lhs: T) -> R: ... method. With this, the twice function can written as:

Python 3.10	Python 3.12+
from typing import Literal from typing import TypeAlias, TypeVar from optype import CanRMul R = TypeVar("R") Two: TypeAlias = Literal[2] RMul2: TypeAlias = CanRMul[Two, R] def twice(x: RMul2[R]) -> R: return 2 * x	from typing import Literal from optype import CanRMul type Two = Literal[2] type RMul2[R] = CanRMul[Two, R] def twice[R](x: RMul2[R]) -> R: return 2 * x

But what about types that implement __add__ but not __radd__? In this case, we could return x * 2 as fallback (assuming commutativity). Because the optype.Can* protocols are runtime-checkable, the revised twice2 function can be compactly written as:

Python 3.10	Python 3.12+
from optype import CanMul Mul2: TypeAlias = CanMul[Two, R] CMul2: TypeAlias = Mul2[R] | RMul2[R] def twice2(x: CMul2[R]) -> R: if isinstance(x, CanRMul): return 2 * x else: return x * 2	from optype import CanMul type Mul2[R] = CanMul[Two, R] type CMul2[R] = Mul2[R] | RMul2[R] def twice2[R](x: CMul2[R]) -> R: if isinstance(x, CanRMul): return 2 * x else: return x * 2

See examples/twice.py for the full example.

Reference

The API of optype is flat; a single import optype as opt is all you need (except for optype.numpy).

• optype
  • Builtin type conversion
  • Rich relations
  • Binary operations
  • Reflected operations
  • Inplace operations
  • Unary operations
  • Rounding
  • Callables
  • Iteration
  • Awaitables
  • Async Iteration
  • Containers
  • Attributes
  • Context managers
  • Descriptors
  • Buffer types
• optype.copy
• optype.dataclasses
• optype.inspect
• optype.json
• optype.pickle
• optype.string
• optype.typing
  • Any* type aliases
  • Empty* type aliases
  • Literal types
• optype.dlpack
• optype.numpy
  • Array
  • UFunc
  • Shape type aliases
  • Scalar
  • DType
  • Any*Array and Any*DType
  • Low-level interfaces

optype

There are four flavors of things that live within optype,

• optype.Can{} types describe what can be done with it. For instance, any CanAbs[T] type can be used as argument to the abs() builtin function with return type T. Most Can{} implement a single special method, whose name directly matched that of the type. CanAbs implements __abs__, CanAdd implements __add__, etc.
• optype.Has{} is the analogue of Can{}, but for special attributes. HasName has a __name__ attribute, HasDict has a __dict__, etc.
• optype.Does{} describe the type of operators. So DoesAbs is the type of the abs({}) builtin function, and DoesPos the type of the +{} prefix operator.
• optype.do_{} are the correctly-typed implementations of Does{}. For each do_{} there is a Does{}, and vice-versa. So do_abs: DoesAbs is the typed alias of abs({}), and do_pos: DoesPos is a typed version of operator.pos. The optype.do_ operators are more complete than operators, have runtime-accessible type annotations, and have names you don't need to know by heart.

The reference docs are structured as follows:

All typing protocols here live in the root optype namespace. They are runtime-checkable so that you can do e.g. isinstance('snail', optype.CanAdd), in case you want to check whether snail implements __add__.

Unlikecollections.abc, optype's protocols aren't abstract base classes, i.e. they don't extend abc.ABC, only typing.Protocol. This allows the optype protocols to be used as building blocks for .pyi type stubs.

Builtin type conversion

The return type of these special methods is invariant. Python will raise an error if some other (sub)type is returned. This is why these optype interfaces don't accept generic type arguments.

operator			operand
expression	function	type	method	type
complex(_)	do_complex	DoesComplex	__complex__	CanComplex
float(_)	do_float	DoesFloat	__float__	CanFloat
int(_)	do_int	DoesInt	__int__	CanInt[R: int = int]
bool(_)	do_bool	DoesBool	__bool__	CanBool[R: bool = bool]
bytes(_)	do_bytes	DoesBytes	__bytes__	CanBytes[R: bytes = bytes]
str(_)	do_str	DoesStr	__str__	CanStr[R: str = str]

Note

The Can* interfaces of the types that can used as typing.Literal accept an optional type parameter R. This can be used to indicate a literal return type, for surgically precise typing, e.g. None, True, and 42 are instances of CanBool[Literal[False]], CanInt[Literal[1]], and CanStr[Literal['42']], respectively.

These formatting methods are allowed to return instances that are a subtype of the str builtin. The same holds for the __format__ argument. So if you're a 10x developer that wants to hack Python's f-strings, but only if your type hints are spot-on; optype is you friend.

operator			operand
expression	function	type	method	type
repr(_)	do_repr	DoesRepr	__repr__	CanRepr[R: str = str]
format(_, x)	do_format	DoesFormat	__format__	CanFormat[T: str = str, R: str = str]

Additionally, optype provides protocols for types with (custom) hash or index methods:

operator			operand
expression	function	type	method	type
hash(_)	do_hash	DoesHash	__hash__	CanHash
_.__index__() (docs)	do_index	DoesIndex	__index__	CanIndex[R: int = int]

Rich relations

The "rich" comparison special methods often return a bool. However, instances of any type can be returned (e.g. a numpy array). This is why the corresponding optype.Can* interfaces accept a second type argument for the return type, that defaults to bool when omitted. The first type parameter matches the passed method argument, i.e. the right-hand side operand, denoted here as x.

operator				operand
expression	reflected	function	type	method	type
_ == x	x == _	do_eq	DoesEq	__eq__	CanEq[T = object, R = bool]
_ != x	x != _	do_ne	DoesNe	__ne__	CanNe[T = object, R = bool]
_ < x	x > _	do_lt	DoesLt	__lt__	CanLt[T, R = bool]
_ <= x	x >= _	do_le	DoesLe	__le__	CanLe[T, R = bool]
_ > x	x < _	do_gt	DoesGt	__gt__	CanGt[T, R = bool]
_ >= x	x <= _	do_ge	DoesGe	__ge__	CanGe[T, R = bool]

Binary operations

In the Python docs, these are referred to as "arithmetic operations". But the operands aren't limited to numeric types, and because the operations aren't required to be commutative, might be non-deterministic, and could have side-effects. Classifying them "arithmetic" is, at the very least, a bit of a stretch.

operator			operand
expression	function	type	method	type
_ + x	do_add	DoesAdd	__add__	CanAdd[T, R]
_ - x	do_sub	DoesSub	__sub__	CanSub[T, R]
_ * x	do_mul	DoesMul	__mul__	CanMul[T, R]
_ @ x	do_matmul	DoesMatmul	__matmul__	CanMatmul[T, R]
_ / x	do_truediv	DoesTruediv	__truediv__	CanTruediv[T, R]
_ // x	do_floordiv	DoesFloordiv	__floordiv__	CanFloordiv[T, R]
_ % x	do_mod	DoesMod	__mod__	CanMod[T, R]
divmod(_, x)	do_divmod	DoesDivmod	__divmod__	CanDivmod[T, R]
_ ** x pow(_, x)	do_pow/2	DoesPow	__pow__	CanPow2[T, R] CanPow[T, None, R, Never]
pow(_, x, m)	do_pow/3	DoesPow	__pow__	CanPow3[T, M, R] CanPow[T, M, Never, R]
_ << x	do_lshift	DoesLshift	__lshift__	CanLshift[T, R]
_ >> x	do_rshift	DoesRshift	__rshift__	CanRshift[T, R]
_ & x	do_and	DoesAnd	__and__	CanAnd[T, R]
_ ^ x	do_xor	DoesXor	__xor__	CanXor[T, R]
_ | x	do_or	DoesOr	__or__	CanOr[T, R]

Note

Because pow() can take an optional third argument, optype provides separate interfaces for pow() with two and three arguments. Additionally, there is the overloaded intersection type CanPow[T, M, R, RM] =: CanPow2[T, R] & CanPow3[T, M, RM], as interface for types that can take an optional third argument.

Reflected operations

For the binary infix operators above, optype additionally provides interfaces with reflected (swapped) operands, e.g. __radd__ is a reflected __add__. They are named like the original, but prefixed with CanR prefix, i.e. __name__.replace('Can', 'CanR').

operator			operand
expression	function	type	method	type
x + _	do_radd	DoesRAdd	__radd__	CanRAdd[T, R]
x - _	do_rsub	DoesRSub	__rsub__	CanRSub[T, R]
x * _	do_rmul	DoesRMul	__rmul__	CanRMul[T, R]
x @ _	do_rmatmul	DoesRMatmul	__rmatmul__	CanRMatmul[T, R]
x / _	do_rtruediv	DoesRTruediv	__rtruediv__	CanRTruediv[T, R]
x // _	do_rfloordiv	DoesRFloordiv	__rfloordiv__	CanRFloordiv[T, R]
x % _	do_rmod	DoesRMod	__rmod__	CanRMod[T, R]
divmod(x, _)	do_rdivmod	DoesRDivmod	__rdivmod__	CanRDivmod[T, R]
x ** _ pow(x, _)	do_rpow	DoesRPow	__rpow__	CanRPow[T, R]
x << _	do_rlshift	DoesRLshift	__rlshift__	CanRLshift[T, R]
x >> _	do_rrshift	DoesRRshift	__rrshift__	CanRRshift[T, R]
x & _	do_rand	DoesRAnd	__rand__	CanRAnd[T, R]
x ^ _	do_rxor	DoesRXor	__rxor__	CanRXor[T, R]
x | _	do_ror	DoesROr	__ror__	CanROr[T, R]

Note

CanRPow corresponds to CanPow2; the 3-parameter "modulo" pow does not reflect in Python.

According to the relevant python docs:

Note that ternary pow() will not try calling __rpow__() (the coercion rules would become too complicated).

Inplace operations

Similar to the reflected ops, the inplace/augmented ops are prefixed with CanI, namely:

operator			operand
expression	function	type	method	types
_ += x	do_iadd	DoesIAdd	__iadd__	CanIAdd[T, R] CanIAddSelf[T]
_ -= x	do_isub	DoesISub	__isub__	CanISub[T, R] CanISubSelf[T]
_ *= x	do_imul	DoesIMul	__imul__	CanIMul[T, R] CanIMulSelf[T]
_ @= x	do_imatmul	DoesIMatmul	__imatmul__	CanIMatmul[T, R] CanIMatmulSelf[T]
_ /= x	do_itruediv	DoesITruediv	__itruediv__	CanITruediv[T, R] CanITruedivSelf[T]
_ //= x	do_ifloordiv	DoesIFloordiv	__ifloordiv__	CanIFloordiv[T, R] CanIFloordivSelf[T]
_ %= x	do_imod	DoesIMod	__imod__	CanIMod[T, R] CanIModSelf[T]
_ **= x	do_ipow	DoesIPow	__ipow__	CanIPow[T, R] CanIPowSelf[T]
_ <<= x	do_ilshift	DoesILshift	__ilshift__	CanILshift[T, R] CanILshiftSelf[T]
_ >>= x	do_irshift	DoesIRshift	__irshift__	CanIRshift[T, R] CanIRshiftSelf[T]
_ &= x	do_iand	DoesIAnd	__iand__	CanIAnd[T, R] CanIAndSelf[T]
_ ^= x	do_ixor	DoesIXor	__ixor__	CanIXor[T, R] CanIXorSelf[T]
_ |= x	do_ior	DoesIOr	__ior__	CanIOr[T, R] CanIOrSelf[T]

These inplace operators usually return itself (after some in-place mutation). But unfortunately, it currently isn't possible to use Self for this (i.e. something like type MyAlias[T] = optype.CanIAdd[T, Self] isn't allowed). So to help ease this unbearable pain, optype comes equipped with ready-made aliases for you to use. They bear the same name, with an additional *Self suffix, e.g. optype.CanIAddSelf[T].

Unary operations

operator			operand
expression	function	type	method	types
+_	do_pos	DoesPos	__pos__	CanPos[R] CanPosSelf
-_	do_neg	DoesNeg	__neg__	CanNeg[R] CanNegSelf
~_	do_invert	DoesInvert	__invert__	CanInvert[R] CanInvertSelf
abs(_)	do_abs	DoesAbs	__abs__	CanAbs[R] CanAbsSelf

Rounding

The round() built-in function takes an optional second argument. From a typing perspective, round() has two overloads, one with 1 parameter, and one with two. For both overloads, optype provides separate operand interfaces: CanRound1[R] and CanRound2[T, RT]. Additionally, optype also provides their (overloaded) intersection type: CanRound[T, R, RT] = CanRound1[R] & CanRound2[T, RT].

operator			operand
expression	function	type	method	type
round(_)	do_round/1	DoesRound	__round__/1	CanRound1[T = int]
round(_, n)	do_round/2	DoesRound	__round__/2	CanRound2[T = int, RT = float]
round(_, n=...)	do_round	DoesRound	__round__	CanRound[T = int, R = int, RT = float]

For example, type-checkers will mark the following code as valid (tested with pyright in strict mode):

x: float = 3.14
x1: CanRound1[int] = x
x2: CanRound2[int, float] = x
x3: CanRound[int, int, float] = x

Furthermore, there are the alternative rounding functions from the math standard library:

operator			operand
expression	function	type	method	type
math.trunc(_)	do_trunc	DoesTrunc	__trunc__	CanTrunc[R = int]
math.floor(_)	do_floor	DoesFloor	__floor__	CanFloor[R = int]
math.ceil(_)	do_ceil	DoesCeil	__ceil__	CanCeil[R = int]

Almost all implementations use int for R. In fact, if no type for R is specified, it will default in int. But technially speaking, these methods can be made to return anything.

Callables

Unlike operator, optype provides the operator for callable objects: optype.do_call(f, *args. **kwargs).

CanCall is similar to collections.abc.Callable, but is runtime-checkable, and doesn't use esoteric hacks.

operator			operand
expression	function	type	method	type
_(*args, **kwargs)	do_call	DoesCall	__call__	CanCall[**Pss, R]

Note

Pyright (and probably other typecheckers) tend to accept collections.abc.Callable in more places than optype.CanCall. This could be related to the lack of co/contra-variance specification for typing.ParamSpec (they should almost always be contravariant, but currently they can only be invariant).

In case you encounter such a situation, please open an issue about it, so we can investigate further.

Iteration

The operand x of iter(_) is within Python known as an iterable, which is what collections.abc.Iterable[V] is often used for (e.g. as base class, or for instance checking).

The optype analogue is CanIter[R], which as the name suggests, also implements __iter__. But unlike Iterable[V], its type parameter R binds to the return type of iter(_) -> R. This makes it possible to annotate the specific type of the iterable that iter(_) returns. Iterable[V] is only able to annotate the type of the iterated value. To see why that isn't possible, see python/typing#548.

The collections.abc.Iterator[V] is even more awkward; it is a subtype of Iterable[V]. For those familiar with collections.abc this might come as a surprise, but an iterator only needs to implement __next__, __iter__ isn't needed. This means that the Iterator[V] is unnecessarily restrictive. Apart from that being theoretically "ugly", it has significant performance implications, because the time-complexity of isinstance on a typing.Protocol is $O(n)$, with the $n$ referring to the amount of members. So even if the overhead of the inheritance and the abc.ABC usage is ignored, collections.abc.Iterator is twice as slow as it needs to be.

That's one of the (many) reasons that optype.CanNext[V] and optype.CanNext[V] are the better alternatives to Iterable and Iterator from the abracadabra collections. This is how they are defined:

operator			operand
expression	function	type	method	type
next(_)	do_next	DoesNext	__next__	CanNext[V]
iter(_)	do_iter	DoesIter	__iter__	CanIter[R: CanNext[object]]

For the sake of compatibility with collections.abc, there is optype.CanIterSelf[V], which is a protocol whose __iter__ returns typing.Self, as well as a __next__ method that returns T. I.e. it is equivalent to collections.abc.Iterator[V], but without the abc nonsense.

Awaitables

The optype is almost the same as collections.abc.Awaitable[R], except that optype.CanAwait[R] is a pure interface, whereas Awaitable is also an abstract base class (making it absolutely useless when writing stubs).

operator	operand
expression	method	type
await _	__await__	CanAwait[R]

Async Iteration

Yes, you guessed it right; the abracadabra collections made the exact same mistakes for the async iterablors (or was it "iteramblers"...?).

But fret not; the optype alternatives are right here:

operator			operand
expression	function	type	method	type
anext(_)	do_anext	DoesANext	__anext__	CanANext[V]
aiter(_)	do_aiter	DoesAIter	__aiter__	CanAIter[R: CanAnext[object]]

But wait, shouldn't V be a CanAwait? Well, only if you don't want to get fired... Technically speaking, __anext__ can return any type, and anext will pass it along without nagging (instance checks are slow, now stop bothering that liberal). For details, see the discussion at python/typeshed#7491. Just because something is legal, doesn't mean it's a good idea (don't eat the yellow snow).

Additionally, there is optype.CanAIterSelf[R], with both the __aiter__() -> Self and the __anext__() -> V methods.

Containers

operator			operand
expression	function	type	method	type
len(_)	do_len	DoesLen	__len__	CanLen[R: int = int]
_.__length_hint__() (docs)	do_length_hint	DoesLengthHint	__length_hint__	CanLengthHint[R: int = int]
_[k]	do_getitem	DoesGetitem	__getitem__	CanGetitem[K, V]
_.__missing__() (docs)	do_missing	DoesMissing	__missing__	CanMissing[K, D]
_[k] = v	do_setitem	DoesSetitem	__setitem__	CanSetitem[K, V]
del _[k]	do_delitem	DoesDelitem	__delitem__	CanDelitem[K]
k in _	do_contains	DoesContains	__contains__	CanContains[K = object]
reversed(_)	do_reversed	DoesReversed	__reversed__	CanReversed[R], or CanSequence[I, V, N = int]

Because CanMissing[K, D] generally doesn't show itself without CanGetitem[K, V] there to hold its hand, optype conveniently stitched them together as optype.CanGetMissing[K, V, D=V].

Similarly, there is optype.CanSequence[K: CanIndex | slice, V], which is the combination of both CanLen and CanItem[I, V], and serves as a more specific and flexible collections.abc.Sequence[V].

Attributes

operator			operand
expression	function	type	method	type
v = _.k or v = getattr(_, k)	do_getattr	DoesGetattr	__getattr__	CanGetattr[K: str = str, V = object]
_.k = v or setattr(_, k, v)	do_setattr	DoesSetattr	__setattr__	CanSetattr[K: str = str, V = object]
del _.k or delattr(_, k)	do_delattr	DoesDelattr	__delattr__	CanDelattr[K: str = str]
dir(_)	do_dir	DoesDir	__dir__	CanDir[R: CanIter[CanIterSelf[str]]]

Context managers

Support for the with statement.

operator	operand
expression	method(s)	type(s)
	__enter__	CanEnter[C], or CanEnterSelf
	__exit__	CanExit[R = None]
with _ as c:	__enter__, and __exit__	CanWith[C, R=None], or CanWithSelf[R=None]

CanEnterSelf and CanWithSelf are (runtime-checkable) aliases for CanEnter[Self] and CanWith[Self, R], respectively.

For the async with statement the interfaces look very similar:

operator	operand
expression	method(s)	type(s)
	__aenter__	CanAEnter[C], or CanAEnterSelf
	__aexit__	CanAExit[R=None]
async with _ as c:	__aenter__, and __aexit__	CanAsyncWith[C, R=None], or CanAsyncWithSelf[R=None]

Descriptors

Interfaces for descriptors.

operator	operand
expression	method	type
v: V = T().d vt: VT = T.d	__get__	CanGet[T: object, V, VT = V]
T().k = v	__set__	CanSet[T: object, V]
del T().k	__delete__	CanDelete[T: object]
class T: d = _	__set_name__	CanSetName[T: object, N: str = str]

Buffer types

Interfaces for emulating buffer types using the buffer protocol.

operator	operand
expression	method	type
v = memoryview(_)	__buffer__	CanBuffer[T: int = int]
del v	__release_buffer__	CanReleaseBuffer

optype.copy

For the copy standard library, optype.copy provides the following runtime-checkable interfaces:

copy standard library	optype.copy
function	type	method
copy.copy(_) -> R	__copy__() -> R	CanCopy[R]
copy.deepcopy(_, memo={}) -> R	__deepcopy__(memo, /) -> R	CanDeepcopy[R]
copy.replace(_, /, **changes: V) -> R [1]	__replace__(**changes: V) -> R	CanReplace[V, R]

^[1] copy.replace requires python>=3.13 (but optype.copy.CanReplace doesn't)

In practice, it makes sense that a copy of an instance is the same type as the original. But because typing.Self cannot be used as a type argument, this difficult to properly type. Instead, you can use the optype.copy.Can{}Self types, which are the runtime-checkable equivalents of the following (recursive) type aliases:

type CanCopySelf = CanCopy[CanCopySelf]
type CanDeepcopySelf = CanDeepcopy[CanDeepcopySelf]
type CanReplaceSelf[V] = CanReplace[V, CanReplaceSelf[V]]

optype.dataclasses

For the dataclasses standard library, optype.dataclasses provides the HasDataclassFields[V: Mapping[str, Field]] interface. It can conveniently be used to check whether a type or instance is a dataclass, i.e. isinstance(obj, HasDataclassFields).

optype.inspect

A collection of functions for runtime inspection of types, modules, and other objects.

Function	Description
get_args(_)	A better alternative to typing.get_args(), that unpacks typing.Annotated and Python 3.12 type _ alias types (i.e. typing.TypeAliasType), recursively flattens unions and nested typing.Literal types, and raises TypeError if not a type expression. Return a tuple[type | object, ...] of type arguments or parameters. To illustrate one of the (many) issues with typing.get_args: >>> from typing import Literal, TypeAlias, get_args >>> Falsy: TypeAlias = Literal[None] | Literal[False, 0] | Literal["", b""] >>> get_args(Falsy) (typing.Literal[None], typing.Literal[False, 0], typing.Literal['', b'']) But this is in direct contradiction with the official typing documentation: When a Literal is parameterized with more than one value, it’s treated as exactly equivalent to the union of those types. That is, Literal[v1, v2, v3] is equivalent to Literal[v1] | Literal[v2] | Literal[v3]. So this is why optype.inspect.get_args should be used >>> import optype as opt >>> opt.inspect.get_args(Falsy) (None, False, 0, '', b'') Another issue of typing.get_args is with Python 3.12 type _ = ... aliases, which are meant as a replacement for _: typing.TypeAlias = ..., and should therefore be treated equally: >>> import typing >>> import optype as opt >>> type StringLike = str | bytes >>> typing.get_args(StringLike) () >>> opt.inspect.get_args(StringLike) (<class 'str'>, <class 'bytes'>) Clearly, typing.get_args fails misarably here; it would have been better if it would have raised an error, but it instead returns an empty tuple, hiding the fact that it doesn't support the new type _ = ... aliases. But luckily, optype.inspect.get_args doesn't have this problem, and treats it just like it treats typing.Alias (and so do the other optype.inspect functions).
get_protocol_members(_)	A better alternative to typing.get_protocol_members(), that doesn't require Python 3.13 or above, supports PEP 695 type _ alias types on Python 3.12 and above, unpacks unions of typing.Literal ... ... and flattens them if nested within another typing.Literal, treats typing.Annotated[T] as T, and raises a TypeError if the passed value isn't a type expression. Returns a frozenset[str] with member names.
get_protocols(_)	Returns a frozenset[type] of the public protocols within the passed module. Pass private=True to also return the private protocols.
is_iterable(_)	Check whether the object can be iterated over, i.e. if it can be used in a for loop, without attempting to do so. If True is returned, then the object is a optype.typing.AnyIterable instance.
is_final(_)	Check if the type, method / classmethod / staticmethod / property, is decorated with @typing.final. Note that a @property won't be recognized unless the @final decorator is placed below the @property decorator. See the function docstring for more information.
is_protocol(_)	A backport of typing.is_protocol that was added in Python 3.13, a re-export of typing_extensions.is_protocol.
is_runtime_protocol(_)	Check if the type expression is a runtime-protocol, i.e. a typing.Protocol type, decorated with @typing.runtime_checkable (also supports typing_extensions).
is_union_type(_)	Check if the type is a typing.Union type, e.g. str | int. Unlike isinstance(_, types.Union), this function also returns True for unions of user-defined Generic or Protocol types (because those are different union types for some reason).
is_generic_alias(_)	Check if the type is a subscripted type, e.g. list[str] or optype.CanNext[int], but not list, CanNext. Unlike isinstance(_, typing.GenericAlias), this function also returns True for user-defined Generic or Protocol types (because those are use a different generic alias for some reason). Even though technically T1 | T2 is represented as typing.Union[T1, T2] (which is a (special) generic alias), is_generic_alias will returns False for such union types, because calling T1 | T2 a subscripted type just doesn't make much sense.

Note

All functions in optype.inspect also work for Python 3.12 type _ aliases (i.e. types.TypeAliasType) and with typing.Annotated.

optype.json

Type aliases for the json standard library:

Value	AnyValue
json.load(s) return type	json.dumps(s) input type
Array[V: Value = Value]	AnyArray[V: AnyValue = AnyValue]
Object[V: Value = Value]	AnyObject[V: AnyValue = AnyValue]

The (Any)Value can be any json input, i.e. Value | Array | Object is equivalent to Value. It's also worth noting that Value is a subtype of AnyValue, which means that AnyValue | Value is equivalent to AnyValue.

optype.pickle

For the pickle standard library, optype.pickle provides the following interfaces:

method(s)	signature (bound)	type
__reduce__	() -> R	CanReduce[R: str | tuple = ...]
__reduce_ex__	(CanIndex) -> R	CanReduceEx[R: str | tuple = ...]
__getstate__	() -> S	CanGetstate[S]
__setstate__	(S) -> None	CanSetstate[S]
__getnewargs__ __new__	() -> tuple[V, ...] (V) -> Self	CanGetnewargs[V]
__getnewargs_ex__ __new__	() -> tuple[tuple[V, ...], dict[str, KV]] (*tuple[V, ...], **dict[str, KV]) -> Self	CanGetnewargsEx[V, KV]

optype.string

The string standard library contains practical constants, but it has two issues:

• The constants contain a collection of characters, but are represented as a single string. This makes it practically impossible to type-hint the individual characters, so typeshed currently types these constants as a LiteralString.
• The names of the constants are inconsistent, and doesn't follow PEP 8.

So instead, optype.string provides an alternative interface, that is compatible with string, but with slight differences:

• For each constant, there is a corresponding Literal type alias for the individual characters. Its name matches the name of the constant, but is singular instead of plural.
• Instead of a single string, optype.string uses a tuple of characters, so that each character has its own typing.Literal annotation. Note that this is only tested with (based)pyright / pylance, so it might not work with mypy (it has more bugs than it has lines of codes).
• The names of the constant are consistent with PEP 8, and use a postfix notation for variants, e.g. DIGITS_HEX instead of hexdigits.
• Unlike string, optype.string has a constant (and type alias) for binary digits '0' and '1'; DIGITS_BIN (and DigitBin). Because besides oct and hex functions in builtins, there's also the builtins.bin function.

string._		optype.string._
constant	char type	constant	char type
missing		DIGITS_BIN	DigitBin
octdigits	LiteralString	DIGITS_OCT	DigitOct
digits		DIGITS	Digit
hexdigits		DIGITS_HEX	DigitHex
ascii_letters		LETTERS	Letter
ascii_lowercase		LETTERS_LOWER	LetterLower
ascii_uppercase		LETTERS_UPPER	LetterUpper
punctuation		PUNCTUATION	Punctuation
whitespace		WHITESPACE	Whitespace
printable		PRINTABLE	Printable

Each of the optype.string constants is exactly the same as the corresponding string constant (after concatenation / splitting), e.g.

>>> import string
>>> import optype as opt
>>> "".join(opt.string.PRINTABLE) == string.printable
True
>>> tuple(string.printable) == opt.string.PRINTABLE
True

Similarly, the values within a constant's Literal type exactly match the values of its constant:

>>> import optype as opt
>>> from optype.inspect import get_args
>>> get_args(opt.string.Printable) == opt.string.PRINTABLE
True

The optype.inspect.get_args is a non-broken variant of typing.get_args that correctly flattens nested literals, type-unions, and PEP 695 type aliases, so that it matches the official typing specs. In other words; typing.get_args is yet another fundamentally broken python-typing feature that's useless in the situations where you need it most.

optype.typing

Any* type aliases

Type aliases for anything that can always be passed to int, float, complex, iter, or typing.Literal

Python constructor	optype.typing alias
int(_)	AnyInt
float(_)	AnyFloat
complex(_)	AnyComplex
iter(_)	AnyIterable
typing.Literal[_]	AnyLiteral

Note

Even though some str and bytes can be converted to int, float, complex, most of them can't, and are therefore not included in these type aliases.

Empty* type aliases

These are builtin types or collections that are empty, i.e. have length 0 or yield no elements.

instance	optype.typing type
''	EmptyString
b''	EmptyBytes
()	EmptyTuple
[]	EmptyList
{}	EmptyDict
set()	EmptySet
(i for i in range(0))	EmptyIterable

Literal types

Literal values	optype.typing type	Notes
{False, True}	LiteralFalse	Similar to typing.LiteralString, but for bool.
{0, 1, ..., 255}	LiteralByte	Integers in the range 0-255, that make up a bytes or bytearray objects.

optype.dlpack

A collection of low-level types for working DLPack.

Protocols

type signature	bound method
CanDLPack[ +T = int, +D: int = int, ]	def __dlpack__( *, stream: int | None = ..., max_version: tuple[int, int] | None = ..., dl_device: tuple[T, D] | None = ..., copy: bool | None = ..., ) -> types.CapsuleType: ...
CanDLPackDevice[ +T = int, +D: int = int, ]	def __dlpack_device__() -> tuple[T, D]: ...

The + prefix indicates that the type parameter is covariant.

Enums

There are also two convenient IntEnums in optype.dlpack: DLDeviceType for the device types, and DLDataTypeCode for the internal type-codes of the DLPack data types.

optype.numpy

Optype supports both NumPy 1 and 2. The current minimum supported version is 1.24, following NEP 29 and SPEC 0.

When using optype.numpy, it is recommended to install optype with the numpy extra, ensuring version compatibility:

pip install "optype[numpy]"

Note

For the remainder of the optype.numpy docs, assume that the following import aliases are available.

from typing import Any, Literal
import numpy as np
import numpy.typing as npt
import optype.numpy as onp

For the sake of brevity and readability, the PEP 695 and PEP 696 type parameter syntax will be used, which is supported since Python 3.13.

Array

Optype provides the generic onp.Array type alias for np.ndarray. It is similar to npt.NDArray, but includes two (optional) type parameters: one that matches the shape type (ND: tuple[int, ...]), and one that matches the scalar type (ST: np.generic).

When put the definitions of npt.NDArray and onp.Array side-by-side, their differences become clear:

numpy.typing.NDArray	optype.numpy.Array
type NDArray[ # no shape type ST: np.generic, # no default ] = np.ndarray[Any, np.dtype[ST]]	type Array[ ND: tuple[int, ...] = tuple[int, ...], ST: np.generic = np.generic, ] = np.ndarray[ND, np.dtype[ST]]

Important

The shape type parameter (ND) of np.ndarray is currently defined as invariant. This is incorrect: it should be covariant.

This means that ND: tuple[int, ...] is also invariant in onp.Array.

The consequence is that e.g. def span(a: onp.Array[tuple[int], ST]), won't accept onp.Array[tuple[Literal[42]]] as argument, even though Literal[42] is a subtype of int.

See numpy/numpy#25729 and numpy/numpy#26081 for details.

In fact, `onp.Array` is *almost* a generalization of `npt.NDArray`.

This is because npt.NDArray can be defined purely in terms of onp.Array (but not vice-versa).

type NDArray[ST: np.generic] = onp.Array[Any, ST]

With onp.Array, it becomes possible to type the shape of arrays,

Note

A little bird told me that onp.Array might be backported to NumPy in the near future.

UFunc

A large portion of numpy's public API consists of universal functions, often denoted as ufuncs, which are (callable) instances of np.ufunc.

Tip

Custom ufuncs can be created using np.frompyfunc, but also through a user-defined class that implements the required attributes and methods (i.e., duck typing).

But np.ufunc has a big issue; it accepts no type parameters. This makes it very difficult to properly annotate its callable signature and its literal attributes (e.g. .nin and .identity).

This is where optype.numpy.UFunc comes into play: It's a runtime-checkable generic typing protocol, that has been thoroughly type- and unit-tested to ensure compatibility with all of numpy's ufunc definitions. Its generic type signature looks roughly like:

type UFunc[
    # The type of the (bound) `__call__` method.
    Fn: CanCall = CanCall,
    # The types of the `nin` and `nout` (readonly) attributes.
    # Within numpy these match either `Literal[1]` or `Literal[2]`.
    Nin: int = int,
    Nout: int = int,
    # The type of the `signature` (readonly) attribute;
    # Must be `None` unless this is a generalized ufunc (gufunc), e.g.
    # `np.matmul`.
    Sig: str | None = str | None,
    # The type of the `identity` (readonly) attribute (used in `.reduce`).
    # Unless `Nin: Literal[2]`, `Nout: Literal[1]`, and `Sig: None`,
    # this should always be `None`.
    # Note that `complex` also includes `bool | int | float`.
    Id: complex | bytes | str | None = float | None,
] = ...

Note

Unfortunately, the extra callable methods of np.ufunc (at, reduce, reduceat, accumulate, and outer), are incorrectly annotated (as None attributes, even though at runtime they're methods that raise a ValueError when called). This currently makes it impossible to properly type these in optype.numpy.UFunc; doing so would make it incompatible with numpy's ufuncs.

Shape type aliases

A shape is nothing more than a tuple of (non-negative) integers, i.e. an instance of tuple[int, ...] such as (42,), (6, 6, 6) or (). The length of a shape is often referred to as the number of dimensions or the dimensionality of the array or scalar. For arrays this is accessible through the np.ndarray.ndim, which is an alias for len(np.ndarray.shape).

Note

Before NumPy 2, the maximum number of dimensions was 32, but has since been increased to 64.

To make typing the shape of an array easier, optype provides two families of shape type aliases: AtLeast{N}D and AtMost{N}D. The {N} should be replaced by the number of dimensions, which currently is limited to 0, 1, 2, and 3.

Both of these families are generic, and their (optional) type parameters must be either int (default), or a literal (non-negative) integer, i.e. like typing.Literal[N: int].

Note

NumPy's functions with a shape parameter usually also accept a "base" int, which is shorthand for tuple[int]. But for the sake of consistency, AtLeast{N}D and AtMost{N}D are limited to integer tuples.

The names AtLeast{N}D and AtMost{N}D are pretty much as self-explanatory:

• AtLeast{N}D is a tuple[int, ...] with ndim >= N
• AtMost{N}D is a tuple[int, ...] with ndim <= N

The shape aliases are roughly defined as:

AtLeast{N}D		AtMost{N}D
type signature	alias type	type signature	type alias
type AtLeast0D[ Ds: int = int, ] = _	tuple[Ds, ...]	type AtMost0D = _	tuple[()]
type AtLeast1D[ D0: int = int, Ds: int = int, ] = _	tuple[ D0, *tuple[Ds, ...], ]	type AtMost1D[ D0: int = int, ] = _	tuple[D0] | AtMost0D
type AtLeast2D[ D0: int = int, D1: int = int, Ds: int = int, ] = _	tuple[ D0, D1, *tuple[Ds, ...], ]	type AtMost2D[ D0: int = int, D1: int = int, ] = _	( tuple[D0, D1] | AtMost1D[D0] )
type AtLeast3D[ D0: int = int, D1: int = int, D2: int = int, Ds: int = int, ] = _	tuple[ D0, D1, D2, *tuple[Ds, ...], ]	type AtMost3D[ D0: int = int, D1: int = int, D2: int = int, ] = _	( tuple[D0, D1, D2] | AtMost2D[D0, D1] )

Scalar

The optype.numpy.Scalar interface is a generic runtime-checkable protocol, that can be seen as a "more specific" np.generic, both in name, and from a typing perspective.

Its type signature looks roughly like this:

type Scalar[
    # The "Python type", so that `Scalar.item() -> PT`.
    PT: object,
    # The "N-bits" type (without having to deal with `npt.NBitBase`).
    # It matches the `itemsize: NB` property.
    NB: int = int,
] = ...

It can be used as e.g.

are_birds_real: Scalar[bool, Literal[1]] = np.bool_(True)
the_answer: Scalar[int, Literal[2]] = np.uint16(42)
alpha: Scalar[float, Literal[8]] = np.float64(1 / 137)

Note

The second type argument for itemsize can be omitted, which is equivalent to setting it to int, so Scalar[PT] and Scalar[PT, int] are equivalent.

DType

In NumPy, a dtype (data type) object, is an instance of the numpy.dtype[ST: np.generic] type. It's commonly used to convey metadata of a scalar type, e.g. within arrays.

Because the type parameter of np.dtype isn't optional, it could be more convenient to use the alias optype.numpy.DType, which is defined as:

type DType[ST: np.generic = np.generic] = np.dtype[ST]

Apart from the "CamelCase" name, the only difference with np.dtype is that the type parameter can be omitted, in which case it's equivalent to np.dtype[np.generic], but shorter.

Any*Array and Any*DType

The Any{Scalar}Array type aliases describe everything that, when passed to numpy.asarray (or any other numpy.ndarray constructor), results in a numpy.ndarray with specific dtype, i.e. numpy.dtypes.{Scalar}DType.

Note

The numpy.dtypes docs exists since NumPy 1.25, but its type annotations were incorrect before NumPy 2.1 (see numpy/numpy#27008)

See the docs for more info on the NumPy scalar type hierarchy.

Abstract types

numpy._		optype.numpy._
scalar type	base type	array-like type	dtype-like type
generic		AnyArray	AnyDType
number	generic	AnyNumberArray	AnyNumberDType
integer	number	AnyIntegerArray	AnyIntegerDType
inexact		AnyInexactArray	AnyInexactDType
unsignedinteger	integer	AnyUnsignedIntegerArray	AnyUnsignedIntegerDType
signedinteger		AnySignedIntegerArray	AnySignedIntegerDType
floating	inexact	AnyFloatingArray	AnyFloatingDType
complexfloating		AnyComplexFloatingArray	AnyComplexFloatingDType

Unsigned integers

numpy._		optype.numpy._
scalar type	base type	array-like type	dtype-like type
uint8	unsignedinteger	AnyUInt8Array	AnyUInt8DType
uint16		AnyUInt16Array	AnyUInt16DType
uint32		AnyUInt32Array	AnyUInt32DType
uint64		AnyUInt64Array	AnyUInt64DType
uintp		AnyUIntPArray	AnyUIntPDType
ubyte		AnyUByteArray	AnyUByteDType
ushort		AnyUShortArray	AnyUShortDType
uintc		AnyUIntCArray	AnyUIntCDType
ulong		AnyULongArray	AnyULongDType
ulonglong		AnyULongLongArray	AnyULongLongDType

Signed integers

numpy._		optype.numpy._
scalar type	base type	array-like type	dtype-like type
int8	signedinteger	AnyInt8Array	AnyInt8DType
int16		AnyInt16Array	AnyInt16DType
int32		AnyInt32Array	AnyInt32DType
int64		AnyInt64Array	AnyInt64DType
intp		AnyIntPArray	AnyIntPDType
byte		AnyByteArray	AnyByteDType
short		AnyShortArray	AnyShortDType
intc		AnyIntCArray	AnyIntCDType
long		AnyLongArray	AnyLongDType
longlong		AnyLongLongArray	AnyLongLongDType

Floats

numpy._		optype.numpy._
scalar type	base type	array-like type	dtype-like type
float16	floating	AnyFloat16Array	AnyFloat16DType
half
float32		AnyFloat32Array	AnyFloat32DType
single
float64		AnyFloat64Array	AnyFloat64DType
double
longdouble		AnyLongDoubleArray	AnyLongDoubleDType

Complex numbers

numpy._		optype.numpy._
scalar type	base type	array-like type	dtype-like type
complex64	complexfloating	AnyComplex64Array	AnyComplex64DType
csingle
complex128		AnyComplex128Array	AnyComplex128DType
cdouble
clongdouble		AnyCLongDoubleArray	AnyCLongDoubleDType

"Flexible"

Scalar types with "flexible" length, whose values have a (constant) length that depends on the specific np.dtype instantiation.

numpy._		optype.numpy._
scalar type	base type	array-like type	dtype-like type
str_	character	AnyStrArray	AnyStrDType
bytes_		AnyBytesArray	AnyBytesDType
void	flexible	AnyVoidArray	AnyVoidDType

Other types

numpy._		optype.numpy._
scalar type	base type	array-like type	dtype-like type
bool_	generic	AnyBoolArray	AnyBoolDType
datetime64		AnyDateTime64Array	AnyDateTime64DType
timedelta64		AnyTimeDelta64Array	AnyTimeDelta64DType
object_		AnyObjectArray	AnyObjectDType
missing		AnyStringArray	AnyStringDType

Low-level interfaces

Within optype.numpy there are several Can* (single-method) and Has* (single-attribute) protocols, related to the __array_*__ dunders of the NumPy Python API. These typing protocols are, just like the optype.Can* and optype.Has* ones, runtime-checkable and extensible (i.e. not @final).

Tip

All type parameters of these protocols can be omitted, which is equivalent to passing its upper type bound.

Protocol type signature	Implements	NumPy docs
class CanArray[ ND: tuple[int, ...] = ..., ST: np.generic = ..., ]: ...	def __array__[RT = ST]( _, dtype: DType[RT] | None = ..., ) -> Array[ND, RT]	User Guide: Interoperability with NumPy
class CanArrayUFunc[ U: UFunc = ..., R: object = ..., ]: ...	def __array_ufunc__( _, ufunc: U, method: LiteralString, *args: object, **kwargs: object, ) -> R: ...	NEP 13
class CanArrayFunction[ F: CanCall[..., object] = ..., R = object, ]: ...	def __array_function__( _, func: F, types: CanIterSelf[type[CanArrayFunction]], args: tuple[object, ...], kwargs: Mapping[str, object], ) -> R: ...	NEP 18
class CanArrayFinalize[ T: object = ..., ]: ...	def __array_finalize__(_, obj: T): ...	User Guide: Subclassing ndarray
class CanArrayWrap: ...	def __array_wrap__[ND, ST]( _, array: Array[ND, ST], context: (...) | None = ..., return_scalar: bool = ..., ) -> Self | Array[ND, ST]	API: Standard array subclasses
class HasArrayInterface[ V: Mapping[str, object] = ..., ]: ...	__array_interface__: V	API: The array interface protocol
class HasArrayPriority: ...	__array_priority__: float	API: Standard array subclasses
class HasDType[ DT: DType = ..., ]: ...	dtype: DT	API: Specifying and constructing data types