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Minimal Python multidispatch framework
# Minimal Multidispatch example.
# Type safe: if types not included in overload set exception is raised
# Author: Ugo Varetto
# License SPDX: UPL-1.0 (Permissive license)
import sys
def __create_overload_table(obj):
if getattr(obj, '__overload_table', None):
return
else:
setattr(obj, '__overload_table', dict())
def dyn_dispatch(class_type, method_name, *types):
# types: types used to specify the overload keys, no need to match signature
# if signature too long or accepting a variable number of parameters just
# use as few as needed to make the key unique
def decorator(f):
__create_overload_table(class_type)
class_type.__overload_table[(method_name, tuple(t for t in types))] = f
def wrapper(*args):
return f(*args)
wrapper.__name__ = method_name
return wrapper
return decorator
def dyn_method(f):
def wrapper(self, *args):
key = (f.__name__, tuple(type(t) for t in args))
# error checking, remove for faster execution
if not getattr(self, '__overload_table', None):
raise AttributeError(f"No overloaded methods found for '{f.__name__}'")
if key not in self.__overload_table:
raise TypeError(f"No overload found for method '{f.__name__}' with parameter type(s) '{key[1]}'")
return self.__overload_table[key](self, *args)
wrapper.__name__ = f.__name__
return wrapper
def dyn_dispatch_f(fun_name, *types):
# types: types used to specify the overload keys, no need to match signature
# if signature too long or accepting a variable number of parameters just
# use as few as needed to make the key unique
def decorator(f):
module = sys.modules[__name__]
__create_overload_table(module)
module.__overload_table[(fun_name, tuple(t for t in types))] = f
def wrapper(*args):
return f(*args)
wrapper.__name__ = fun_name
return wrapper
return decorator
def dyn_fun(f):
def wrapper(*args):
module = sys.modules[__name__]
key = (f.__name__, tuple(type(t) for t in args))
# error checking, remove for faster execution
if not getattr(module, '__overload_table', None):
raise AttributeError(f"No overloaded methods found for '{f.__name__}'")
if key not in module.__overload_table:
raise TypeError(f"No overload found for method '{f.__name__}' with parameter type(s) '{key[1]}'")
return module.__overload_table[key](*args)
wrapper.__name__ = f.__name__
return wrapper
### Class
class AClass:
def __init__(self, i: int, j: int = 0):
self.i = i
self.j = j
@dyn_method
def set(self, *_):
...
@dyn_dispatch(AClass, 'set', int)
def set_int(self, i: int):
print("set_int called")
self.i = i
@dyn_dispatch(AClass, 'set', float)
def set_float(self, f: float):
print("set_float called")
self.set(int(f))
@dyn_dispatch(AClass, 'set', str)
def set_str(self, s: str):
print("set_str called")
self.set(int(s))
@dyn_dispatch(AClass, 'set', int, int)
def set_int_int(self, i: int, j: int):
print("set_int_int called")
self.i, self.j = i, j
### Function
@dyn_fun
def double(*_):
pass
@dyn_dispatch_f('double', float)
def double_float(f: float) -> float:
print("double_float called")
return 2 * f
@dyn_dispatch_f('double', int)
def double_int(i: int) -> int:
print("double_int called")
return 2 * i
@dyn_dispatch_f('double', str)
def double_str(s: str) -> str:
print("double_str called")
return s + s
if __name__ == "__main__":
print("-" * 10)
print("Class")
print(AClass.__overload_table)
try:
a = AClass(2)
print(a.i)
print()
a.set(1.0)
print(a.i)
a.set("10")
print(a.i)
a.set(6, 7)
print(a.i, a.j)
a.set(6.6, 6.9) # trigger exception no (float, float) overload for set
# a.set(True) #trigger exception no (bool) overload for set
except TypeError as e:
print(e, file=sys.stderr)
print("-" * 10)
print("\nFunction")
print(__overload_table)
try:
print(double(1.4))
print(double(3))
print(double('string'))
print(double(1,2))
except TypeError as e:(
print(e, file=sys.stderr))
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