multimethod/__init__.py
import abc
import collections
import contextlib
import functools
import inspect
import itertools
import types
import typing
import warnings
from collections.abc import Callable, Iterable, Iterator, Mapping
from typing import Any, Literal, Optional, TypeVar, Union, get_type_hints, overload as tp_overload
__version__ = '1.11.2'
class DispatchError(TypeError):
pass
def get_origin(tp):
return tp.__origin__ if isinstance(tp, subtype) else typing.get_origin(tp)
def get_args(tp) -> tuple:
if isinstance(tp, subtype) or typing.get_origin(tp) is Callable:
return getattr(tp, '__args__', ())
return typing.get_args(tp)
def get_mro(cls) -> tuple: # `inspect.getmro` doesn't handle all cases
return type.mro(cls) if isinstance(cls, type) else cls.mro()
class subtype(abc.ABCMeta):
"""A normalized generic type which checks subscripts.
Transforms a generic alias into a concrete type which supports `issubclass` and `isinstance`.
If the type ends up being equivalent to a builtin, the builtin is returned.
"""
__origin__: type
__args__: tuple
def __new__(cls, tp, *args):
if tp is Any:
return object
if hasattr(tp, '__supertype__'): # isinstance(..., NewType) only supported >=3.10
tp = tp.__supertype__
if isinstance(tp, TypeVar):
if not tp.__constraints__:
return object
tp = Union[tp.__constraints__]
origin = get_origin(tp) or tp
if hasattr(types, 'UnionType') and isinstance(tp, types.UnionType):
origin = Union # `|` syntax added in 3.10
args = tuple(map(cls, get_args(tp) or args))
if set(args) <= {object} and not (origin is tuple and args):
return origin
bases = (origin,) if type(origin) in (type, abc.ABCMeta) else ()
if origin is Literal:
bases = (subtype(Union[tuple(map(type, args))]),)
if origin is Union:
counts = collections.Counter()
for arg in args:
counts.update(cls for cls in get_mro(arg) if issubclass(abc.ABCMeta, type(cls)))
bases = tuple(cls for cls in counts if counts[cls] == len(args))[:1]
if origin is Callable and args[:1] == (...,):
args = args[1:]
namespace = {'__origin__': origin, '__args__': args}
return type.__new__(cls, str(tp), bases, namespace)
def __init__(self, tp, *args): ...
def key(self) -> tuple:
return self.__origin__, *self.__args__
def __eq__(self, other) -> bool:
return hasattr(other, '__origin__') and self.key() == subtype.key(other)
def __hash__(self) -> int:
return hash(self.key())
def __subclasscheck__(self, subclass):
origin = get_origin(subclass) or subclass
args = get_args(subclass)
if origin is Literal:
return all(isinstance(arg, self) for arg in args)
if origin is Union:
return all(issubclass(cls, self) for cls in args)
if self.__origin__ is Literal:
return False
if self.__origin__ is Union:
return issubclass(subclass, self.__args__)
if self.__origin__ is Callable:
return (
origin is Callable
and signature(self.__args__[-1:]) <= signature(args[-1:]) # covariant return
and signature(args[:-1]) <= signature(self.__args__[:-1]) # contravariant args
)
return ( # check args first to avoid recursion error: python/cpython#73407
len(args) == len(self.__args__)
and issubclass(origin, self.__origin__)
and all(pair[0] is pair[1] or issubclass(*pair) for pair in zip(args, self.__args__))
)
def __instancecheck__(self, instance):
if self.__origin__ is Literal:
return any(type(arg) == type(instance) and arg == instance for arg in self.__args__)
if self.__origin__ is Union:
return isinstance(instance, self.__args__)
if hasattr(instance, '__orig_class__'): # user-defined generic type
return issubclass(instance.__orig_class__, self)
if self.__origin__ is type: # a class argument is expected
return inspect.isclass(instance) and issubclass(instance, self.__args__)
if not isinstance(instance, self.__origin__) or isinstance(instance, Iterator):
return False
if self.__origin__ is Callable:
return issubclass(subtype(Callable, *get_type_hints(instance).values()), self)
if self.__origin__ is tuple and self.__args__[-1:] != (...,):
if len(instance) != len(self.__args__):
return False
elif issubclass(self, Mapping):
instance = next(iter(instance.items()), ())
else:
instance = itertools.islice(instance, 1)
return all(map(isinstance, instance, self.__args__))
@functools.singledispatch
def origins(self) -> Iterable[type]:
"""Return origin types which would require instance checks.
Provisional custom usage: `subtype.origins.register(<metaclass>, lambda cls: ...)
"""
origin = get_origin(self)
if origin is Literal:
yield from set(map(type, self.__args__))
elif origin is Union:
for arg in self.__args__:
yield from subtype.origins(arg)
elif origin is not None:
yield origin
class parametric(abc.ABCMeta):
"""A type which further customizes `issubclass` and `isinstance` beyond the base type.
Args:
base: base type
funcs: all predicate functions are checked against the instance
attrs: all attributes are checked for equality
"""
def __new__(cls, base: type, *funcs: Callable, **attrs):
return super().__new__(cls, base.__name__, (base,), {'funcs': funcs, 'attrs': attrs})
def __init__(self, *_, **__): ...
def __subclasscheck__(self, subclass):
missing = object()
attrs = getattr(subclass, 'attrs', {})
return (
set(subclass.__bases__).issuperset(self.__bases__) # python/cpython#73407
and set(getattr(subclass, 'funcs', ())).issuperset(self.funcs)
and all(attrs.get(name, missing) == self.attrs[name] for name in self.attrs)
)
def __instancecheck__(self, instance):
missing = object()
return (
isinstance(instance, self.__bases__)
and all(func(instance) for func in self.funcs)
and all(getattr(instance, name, missing) == self.attrs[name] for name in self.attrs)
)
def __and__(self, other):
(base,) = set(self.__bases__ + other.__bases__)
return type(self)(base, *set(self.funcs + other.funcs), **(self.attrs | other.attrs))
subtype.origins.register(parametric, lambda cls: cls.__bases__)
def distance(cls, subclass: type) -> int:
"""Return estimated distance between classes for tie-breaking."""
if get_origin(cls) is Union:
return min(distance(arg, subclass) for arg in cls.__args__)
mro = get_mro(subclass)
return mro.index(cls if cls in mro else object)
class signature(tuple):
"""A tuple of types that supports partial ordering."""
required: int
parents: set
sig: inspect.Signature
def __new__(cls, types: Iterable, required: Optional[int] = None):
return tuple.__new__(cls, map(subtype, types))
def __init__(self, types: Iterable, required: Optional[int] = None):
self.required = len(self) if required is None else required
@classmethod
def from_hints(cls, func: Callable) -> 'signature':
"""Return evaluated type hints for positional parameters in order."""
if not hasattr(func, '__annotations__'):
return cls(())
type_hints = get_type_hints(func)
positionals = {inspect.Parameter.POSITIONAL_ONLY, inspect.Parameter.POSITIONAL_OR_KEYWORD}
params: Iterable = inspect.signature(func).parameters.values()
params = [param for param in params if param.kind in positionals]
# missing annotations are padded with `object`, but trailing objects are unnecessary
indices = [index for index, param in enumerate(params) if param.name in type_hints]
params = params[: max(indices, default=-1) + 1]
hints = [type_hints.get(param.name, object) for param in params]
required = sum(param.default is param.empty for param in params)
return cls(hints, required)
def __le__(self, other: tuple) -> bool:
return self.required <= len(other) and all(map(issubclass, other, self))
def __lt__(self, other: tuple) -> bool:
return self != other and self <= other
def __sub__(self, other: tuple) -> tuple:
"""Return relative distances, assuming self >= other."""
return tuple(map(distance, other, self))
def __rsub__(self, other: tuple) -> tuple:
"""Return relative distances, assuming self <= other."""
return tuple(map(distance, self, other))
def callable(self, *types) -> bool:
"""Check positional arity of associated function signature."""
try:
return not hasattr(self, 'sig') or bool(self.sig.bind_partial(*types))
except TypeError:
return False
def instances(self, *args) -> bool:
"""Return whether all arguments are instances."""
return self.required <= len(args) and all(map(isinstance, args, self))
REGISTERED = TypeVar("REGISTERED", bound=Callable[..., Any])
class multimethod(dict):
"""A callable directed acyclic graph of methods."""
__name__: str
pending: set
generics: list[tuple] # positional bases which require instance checks
def __new__(cls, func):
homonym = inspect.currentframe().f_back.f_locals.get(func.__name__)
if isinstance(homonym, multimethod):
return homonym
self = functools.update_wrapper(dict.__new__(cls), func)
self.pending = set()
self.generics = []
return self
def __init__(self, func: Callable):
try:
self[signature.from_hints(func)] = func
except (NameError, AttributeError):
self.pending.add(func)
@tp_overload
def register(self, __func: REGISTERED) -> REGISTERED: ... # pragma: no cover
@tp_overload
def register(self, *args: type) -> Callable[[REGISTERED], REGISTERED]: ... # pragma: no cover
def register(self, *args) -> Callable:
"""Decorator for registering a function.
Optionally call with types to return a decorator for unannotated functions.
"""
if len(args) == 1 and hasattr(args[0], '__annotations__'):
multimethod.__init__(self, *args)
return self if self.__name__ == args[0].__name__ else args[0]
return lambda func: self.__setitem__(args, func) or func
def __get__(self, instance, owner):
return self if instance is None else types.MethodType(self, instance)
def parents(self, types: tuple) -> set:
"""Find immediate parents of potential key."""
parents = {key for key in list(self) if isinstance(key, signature) and key < types}
return parents - {ancestor for parent in parents for ancestor in parent.parents}
def clean(self):
"""Empty the cache."""
for key in list(self):
if not isinstance(key, signature):
super().__delitem__(key)
def copy(self):
"""Return a new multimethod with the same methods."""
return dict.__new__(type(self)).__ior__(self)
def __setitem__(self, types: tuple, func: Callable):
self.clean()
if not isinstance(types, signature):
types = signature(types)
parents = types.parents = self.parents(types)
with contextlib.suppress(ValueError):
types.sig = inspect.signature(func)
self.pop(types, None) # ensure key is overwritten
for key in self:
if types < key and (not parents or parents & key.parents):
key.parents -= parents
key.parents.add(types)
for index, cls in enumerate(types):
if origins := set(subtype.origins(cls)):
self.generics += [()] * (index + 1 - len(self.generics))
self.generics[index] = tuple(origins.union(self.generics[index]))
super().__setitem__(types, func)
self.__doc__ = self.docstring
def __delitem__(self, types: tuple):
self.clean()
super().__delitem__(types)
for key in self:
if types in key.parents:
key.parents = self.parents(key)
self.__doc__ = self.docstring
def select(self, types: tuple, keys: set[signature]) -> Callable:
keys = {key for key in keys if key.callable(*types)}
funcs = {self[key] for key in keys}
if len(funcs) > 1:
groups = collections.defaultdict(set)
for key in keys:
groups[types - key].add(key)
keys = groups[min(groups)]
funcs = {self[key] for key in keys}
if len(funcs) == 1:
warnings.warn("positional distance tie-breaking is deprecated", DeprecationWarning)
if len(funcs) == 1:
return funcs.pop()
raise DispatchError(f"{self.__name__}: {len(keys)} methods found", types, keys)
def __missing__(self, types: tuple) -> Callable:
"""Find and cache the next applicable method of given types."""
self.evaluate()
types = tuple(map(subtype, types))
if types in self:
return self[types]
return self.setdefault(types, self.select(types, self.parents(types)))
def dispatch(self, *args) -> Callable:
types = tuple(map(type, args))
if not any(map(issubclass, types, self.generics)):
return self[types]
matches = {key for key in list(self) if isinstance(key, signature) and key.instances(*args)}
matches -= {ancestor for match in matches for ancestor in match.parents}
return self.select(types, matches)
def __call__(self, *args, **kwargs):
"""Resolve and dispatch to best method."""
self.evaluate()
func = self.dispatch(*args)
try:
return func(*args, **kwargs)
except TypeError as ex:
raise DispatchError(f"Function {func.__code__}") from ex
def evaluate(self):
"""Evaluate any pending forward references."""
while self.pending:
func = self.pending.pop()
self[signature.from_hints(func)] = func
@property
def docstring(self):
"""a descriptive docstring of all registered functions"""
docs = []
for key, func in self.items():
sig = getattr(key, 'sig', '')
if func.__doc__:
docs.append(f'{func.__name__}{sig}\n {func.__doc__}')
return '\n\n'.join(docs)
RETURN = TypeVar("RETURN")
class multidispatch(multimethod, dict[tuple[type, ...], Callable[..., RETURN]]):
"""Wrapper for compatibility with `functools.singledispatch`.
Only uses the [register][multimethod.multimethod.register] method instead of namespace lookup.
Allows dispatching on keyword arguments based on the first function signature.
"""
signatures: dict[tuple, inspect.Signature]
def __new__(cls, func: Callable[..., RETURN]) -> "multidispatch[RETURN]":
return functools.update_wrapper(dict.__new__(cls), func) # type: ignore
def __init__(self, func: Callable[..., RETURN]) -> None:
self.pending = set()
self.generics = []
self.signatures = {}
self[()] = func
def __get__(self, instance, owner) -> Callable[..., RETURN]:
return self if instance is None else types.MethodType(self, instance) # type: ignore
def __setitem__(self, types: tuple, func: Callable):
super().__setitem__(types, func)
with contextlib.suppress(ValueError):
signature = inspect.signature(func)
self.signatures.setdefault(tuple(signature.parameters), signature)
def __call__(self, *args: Any, **kwargs: Any) -> RETURN:
"""Resolve and dispatch to best method."""
params = args
if kwargs:
for signature in self.signatures.values(): # pragma: no branch
with contextlib.suppress(TypeError):
params = signature.bind(*args, **kwargs).args
break
func = self.dispatch(*params)
return func(*args, **kwargs)
def isa(*types: type) -> Callable:
"""Partially bound `isinstance`."""
types = tuple(map(subtype, types))
return lambda arg: isinstance(arg, types)
class overload(dict):
"""Ordered functions which dispatch based on their annotated predicates."""
pending: set
__get__ = multimethod.__get__
def __new__(cls, func):
namespace = inspect.currentframe().f_back.f_locals
if func.__name__ not in namespace:
warnings.warn("use `parametric(<base>, <func>)` as a type instead", DeprecationWarning)
self = functools.update_wrapper(super().__new__(cls), func)
self.pending = set()
return namespace.get(func.__name__, self)
def __init__(self, func: Callable):
try:
sig = self.signature(func)
except (NameError, AttributeError):
self.pending.add(func)
else:
self[sig] = func
@classmethod
def signature(cls, func: Callable) -> inspect.Signature:
for name, value in get_type_hints(func).items():
if not callable(value) or isinstance(value, type) or hasattr(value, '__origin__'):
func.__annotations__[name] = isa(value)
return inspect.signature(func)
def __call__(self, *args, **kwargs):
"""Dispatch to first matching function."""
while self.pending:
func = self.pending.pop()
self[self.signature(func)] = func
for sig in reversed(self):
try:
arguments = sig.bind(*args, **kwargs).arguments
except TypeError:
continue
if all(
param.annotation is param.empty or param.annotation(arguments[name])
for name, param in sig.parameters.items()
if name in arguments
):
return self[sig](*args, **kwargs)
raise DispatchError("No matching functions found")
def register(self, func: Callable) -> Callable:
"""Decorator for registering a function."""
self.__init__(func) # type: ignore
return self if self.__name__ == func.__name__ else func # type: ignore
class multimeta(type):
"""Convert all callables in namespace to multimethods."""
class __prepare__(dict):
def __init__(*args):
pass
def __setitem__(self, key, value):
if callable(value):
value = getattr(self.get(key), 'register', multimethod)(value)
super().__setitem__(key, value)