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):
...
Alternatively, functions can be explicitly registered in the same style as functools.singledispatch. This syntax is also compatible with mypy, which by default checks that each name is defined once.
@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 collections.abc
and typing
. Subscripted generics are supported:
Union[...]
Mapping[...]
- the first key-value pair is checkedtuple[...]
- all args are checkedIterable[...]
- the first arg is checked
Naturally checking subscripts is slower, but the implementation is optimized, cached, and bypassed if no subscripts are in use in the multimethod.
Dispatch resolution details:
- If an exact match isn't registered, the next closest method is called (and cached).
- If the
issubclass
relation is ambiguous, mro position is used as a tie-breaker. - If there are still ambiguous methods - or none - a custom
TypeError
is raised. - Default and keyword-only parameters may be annotated, but won't affect dispatching.
- A skipped annotation is equivalent to
: object
, which implicitly supports methods by leavingself
blank. - If no types are specified, it will inherently match all arguments.
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. Instead a simple isa
predicate is provided for checking instance type.
from multimethod import isa, overload
@overload
def func(obj: isa(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.
Use 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):
...
Equivalent to:
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]
dev
- Improved checking for TypeErrors
multidispatch
has provisional support for dispatching on keyword arguments
1.5
- Postponed evaluation of nested annotations
- Variable-length tuples of homogeneous type
- Ignore default and keyword-only parameters
- Resolved ambiguous
Union
types - Fixed an issue with name collision when defining a multimethod
- Resolved dispatch errors when annotating parameters with meta-types such as
type
1.4
- Python >=3.6 required
- Expanded support for subscripted type hints
1.3
- Python 3 required
- Support for subscripted ABCs
1.2
- Support for typing generics
- Stricter dispatching consistent with singledispatch
1.1
- Fix for Python 2 typing backport
- Metaclass for automatic multimethods
1.0
- Missing annotations default to object
- Removed deprecated dispatch stacking
0.7
- Forward references allowed in type hints
- Register method
- Overloads with predicate dispatch
0.6
- Multimethods can be defined inside a class
0.5
- Optimized dispatching
- Support for
functools.singledispatch
syntax
0.4
- Dispatch on Python 3 annotations