optype

One protocol, one method.

Building blocks for precise & flexible type hints.

Installation

Optype is available as optype on PyPI:

pip install optype

...

Reference

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__.

[!NOTE] It is bad practice to use a typing.Protocol as base class for your implementation. Because of @typing.runtime_checkable, you can use isinstance either way.

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.

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.

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.

"Rich comparison" operators

These special methods generally a bool. However, instances of any type can be returned.

Attribute access

Iteration

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

The optype analogue is CanIter[Ks], which as the name suggests, also implements __iter__. But unlike Iterable[K], its type parameter Ks binds to the return type of iter(_). This makes it possible to annotate the specific type of the iterable that iter(_) returns. Iterable[K] 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[K] is even more awkward; it is a subtype of Iterable[K]. 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[K] 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:

Containers

For indexing or locating container values, the following special methods are relevant:

[^4]: Although not strictly required, Y@CanReversed should be a CanNext. [LH]: https://docs.python.org/3/reference/datamodel.html#object.__length_hint__ [GM]: https://docs.python.org/3/reference/datamodel.html#object.__missing__ [IX]: https://docs.python.org/3/reference/datamodel.html#object.__index__

Descriptors

Interfaces for descriptors.

Callable objects

Like collections.abc.Callable, but without esoteric hacks.

Numeric operations

For describing things that act like numbers. See the Python docs for more info.

Additionally, there is the intersection type CanPow[X, M, Y2, Y3] =: CanPow2[X, Y2] & CanPow3[X, M, Y3], that overloads both __pow__ method signatures. Note that the 2 and 3 suffixes refer to the arity (#parameters) of the operators.

For the binary infix operators above, optype additionally provides interfaces with reflected (swapped) operands:

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

Similarly, the augmented assignment operators are described by the following optype interfaces:

Additionally, there are the unary arithmetic operators:

The round function comes in two flavors, and their overloaded intersection:

The last "double" signature denotes overloading.

To illustrate; float is a CanRound[int, int, float] and int a CanRound[int, int, int].

And finally, the remaining rounding functions:

Note that the type parameter Y is unbounded, because technically these methods can return any type.

Context managers

Support for the with statement.

In case of errors, the type alias ExcInfo will be tuple[type[E], E, types.TracebackType], where E is some BaseException. On the other hand, if no errors are raised (without being silenced), then Excinfo will be None in triplicate.

Because everyone that enters must also leave (that means you too, Barry), optype provides the intersection type CanWith[V, R] = CanEnter[V] & CanExit[R]. If you're thinking of an insect-themed sect right now, that's ok -- intersection types aren't real (yet..?). To put your mind at ease, here's how it's implemented:

class CanWith[V, R](CanEnter[V], CanExit[R]):
    # You won't find any bugs here :)
    ...

Buffer types

Interfaces for emulating buffer types.

The flags: B parameter accepts integers within the [1, 1023] interval. Note that the CanReleaseBuffer isn't always needed. See the Python docs or inspect.BufferFlags for more info.

Async objects

The optype variant of collections.abc.Awaitable[V]. The only difference is that optype.CanAwait[V] is a pure interface, whereas Awaitable is also an abstract base class.

Async Iteration

Yes, you guessed it right; the abracadabra collections repeated their mistakes with their async iterablors (or something like that).

But fret not, the optype alternatives are right here:

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). Just because something is legal, doesn't mean it's a good idea (don't eat the yellow snow).

Async context managers

Support for the async with statement.

And just like CanWith[V, R] for sync context managers, there is the CanAsyncWith[V, R] = CanAenter[V] & CanAexit[R] intersection type.

Future plans

• Support for Python versions before 3.12.
• A drop-in replacement for the operator standard library, with runtime-accessible type annotations, and more operators.
• More standard library protocols, e.g. copy, dataclasses, pickle.
• Typed mixins for DRY implementation of operator, e.g. for comparison ops GeFromLt, GtFromLe, etc as a typed alternative for functools.total_ordering. Similarly for numeric types, with e.g. __add__ and __neg__ a mixin could generate __pos__ and __sub__, or with __mod__ and __truediv__ a mixin could generate __
• Dependency-free third-party type support, e.g. protocols for numpy's array interface.