Multiple argument dispatching.
Multimethod provides a decorator for adding multiple argument dispatching to functions. The decorator creates a multimethod object as needed, and registers the function with its annotations.
There are several multiple dispatch libraries on PyPI. This one aims for simplicity and speed. With caching of argument types, it should be the fastest pure Python implementation possible.
from multimethod import multimethod @multimethod def func(x: int, y: float): ...
func is now a
multimethod which will delegate to the above function, when called with arguments of the specified types. Subsequent usage will register new types and functions to the existing multimethod of the same name.
@multimethod def func(x: float, y: int): ...
@func.register def _(x: bool, y: bool): ... @func.register(object, bool) @func.register(bool, object) def _(x, y): # stackable without annotations ...
Multimethods are implemented as mappings from signatures to functions, and can be introspected as such.
method[type, ...] # get registered function method[type, ...] = func # register function by explicit types
Multimethods support any types that satisfy the
issubclass relation, including abstract base classes in
typing. Subscripted generics are supported:
Mapping[...]- the first key-value pair is checked
tuple[...]- all args are checked
Iterable[...]- the first arg is checked
Callable[[...], ...]- parameter types are contravariant, return type is covariant
Naturally checking subscripts is slower, but the implementation is optimized, cached, and bypassed if no subscripts are in use in the parameter. Empty iterables match any subscript, but don't special-case how the types are normally resolved.
Dispatch resolution details:
- If an exact match isn't registered, the next closest method is called (and cached).
- If the
issubclassrelation is ambiguous, mro position is used as a tie-breaker.
- If there are still ambiguous methods - or none - a custom
- Default and keyword-only parameters may be annotated, but won't affect dispatching.
- A skipped annotation is equivalent to
- If no types are specified, it will inherently match all arguments.
staticmethod may be used with a multimethod, but must be applied last, i.e., wrapping the final multimethod definition. For class and instance methods,
self participate in the dispatch as usual. They may be left blank when using annotations, otherwise use
object as a placeholder.
class Foo: @multimethod def bar(cls, x: str): ... @classmethod # <- only put this @classmethod here on the final definition @bar.register def _(cls, x: int): ...
Overloads dispatch on annotated predicates. Each predicate is checked in the reverse order of registration.
The implementation is separate from
multimethod due to the different performance characteristics. If an annotation is a type instead of a predicate, it will be converted into an
from multimethod import overload @overload def func(obj: str): ... @overload def func(obj: str.isalnum): ... @overload def func(obj: str.isdigit): ...
multidispatch is a wrapper to provide compatibility with
functools.singledispatch. It requires a base implementation and use of the
register method instead of namespace lookup. It also provisionally supports dispatching on keyword arguments.
metaclass=multimeta to create a class with a special namespace which converts callables to multimethods, and registers duplicate callables with the original.
from multimethod import multimeta class Foo(metaclass=multimeta): def bar(self, x: str): ... def bar(self, x: int): ...
from multimethod import multimethod class Foo: @multimethod def bar(self, x: str): ... @bar.register def bar(self, x: int): ...
% pip install multimethod
100% branch coverage.
% pytest [--cov]
Callablechecks parameters and return type
- Support for
overloadallows types and converts them to an
- Only functions with docstrings combine signatures
- Fixes for subscripted union and literal checks
- Python >=3.7 required
- Improved checking for TypeErrors
multidispatchhas provisional support for dispatching on keyword arguments
multidispatchsupports static analysis of return type
- Fix for forward references and subscripts
- Checking type subscripts is done minimally based on each parameter
- Provisionally dispatch on
- Provisionally empty iterables match subscript
- Postponed evaluation of nested annotations
- Variable-length tuples of homogeneous type
- Ignore default and keyword-only parameters
- Resolved ambiguous
- Fixed an issue with name collision when defining a multimethod
- Resolved dispatch errors when annotating parameters with meta-types such as
- Python >=3.6 required
- Expanded support for subscripted type hints
- Python 3 required
- Support for subscripted ABCs
- Support for typing generics
- Stricter dispatching consistent with singledispatch
- Fix for Python 2 typing backport
- Metaclass for automatic multimethods
- Missing annotations default to object
- Removed deprecated dispatch stacking
- Forward references allowed in type hints
- Register method
- Overloads with predicate dispatch
- Multimethods can be defined inside a class
- Optimized dispatching
- Support for
- Dispatch on Python 3 annotations
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