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singledispatchann.py
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77 lines (63 loc) · 2.44 KB
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from weakref import WeakKeyDictionary
from abc import get_cache_token
from types import MappingProxyType
import inspect
#hack
from functools import _find_impl, update_wrapper
def singledispatchann(func):
"""Single-dispatch generic function decorator.
Transforms a function into a generic function, which can have different
behaviours depending upon the type of its first argument. The decorated
function acts as the default implementation, and additional
implementations can be registered using the register() attribute of the
generic function.
"""
registry = {}
dispatch_cache = WeakKeyDictionary()
cache_token = None
disp_param = 1 if list(inspect.signature(func).parameters.keys())[0] == 'self' else 0
def dispatch(cls):
"""generic_func.dispatch(cls) -> <function implementation>
Runs the dispatch algorithm to return the best available implementation
for the given *cls* registered on *generic_func*.
"""
nonlocal cache_token
if cache_token is not None:
current_token = get_cache_token()
if cache_token != current_token:
dispatch_cache.clear()
cache_token = current_token
try:
impl = dispatch_cache[cls]
except KeyError:
try:
impl = registry[cls]
except KeyError:
impl = _find_impl(cls, registry)
dispatch_cache[cls] = impl
return impl
def register(cls=None, func=None):
"""generic_func.register(cls, func) -> func
Registers a new implementation for the given *cls* on a *generic_func*.
"""
nonlocal cache_token
if func is None:
return lambda f: register(cls, f)
if cls is None:
sign = inspect.signature(func)
params = sign.parameters
cls = list(params.values())[disp_param].annotation
registry[cls] = func
if cache_token is None and hasattr(cls, '__abstractmethods__'):
cache_token = get_cache_token()
dispatch_cache.clear()
return func
def wrapper(*args, **kw):
return dispatch(args[disp_param].__class__)(*args, **kw)
registry[object] = func
wrapper.register = register
wrapper.dispatch = dispatch
wrapper.registry = MappingProxyType(registry)
wrapper._clear_cache = dispatch_cache.clear
update_wrapper(wrapper, func)
return wrapper