我不清楚如何提出这个问题。如果我这样做了，我可能会更接近解决方案。我需要对继承有一些了解。
我想创建一个float 的自定义子类型。但我希望此子类型的实例在执行任何正常的 float 方法(__add__、__mul__ 等)之前重新评估其值。在此示例中，它应将其值乘以全局因子:
class FactorFloat(float):
# I don't think I want to do this:
## def __new__(self, value):
## return float.__new__(self, value)
def __init__(self, value):
float.__init__(self, value)
# Something important is missing..
# I want to do something with global FACTOR
# when any float method is called.
f = FactorFloat(3.)
FACTOR = 10.
print f # 30.0
print f-1 # 29.0
FACTOR = 2.
print f # 6.0
print f-1 # 5.0
这只是一个经过净化的例子，我认为它能说明我的观点。如有必要，我会发布更复杂的“真实”问题。
请您参考如下方法:
class FactorFloat(float):
def _factor_scale(f):
def wrapper(self, *args, **kwargs):
scaled = float.__mul__(self, FACTOR)
result = f(scaled, *args, **kwargs)
# if you want to return FactorFloats when possible:
if isinstance(result, float):
result = type(self)(result/FACTOR)
return result
return wrapper
def __repr__(self):
return '%s(%s)' % (type(self).__name__, float.__repr__(self))
__str__ = _factor_scale(float.__str__)
__mul__ = _factor_scale(float.__mul__)
__div__ = _factor_scale(float.__div__)
__add__ = _factor_scale(float.__add__)
__sub__ = _factor_scale(float.__sub__)
f = FactorFloat(3.)
FACTOR = 10.
print f # 30.0
print f-1 # 29.0
FACTOR = 2.
print f # 6.0
print f-1 # 5.0
print repr(f)
对于:
30.0
29.0
6.0
5.0
FactorFloat(3.0)
编辑:
回应评论中的问题；使用类装饰器使事情变得更加通用和自动化。我不会遍历 dir(baseclass)，而是会明确列出我希望包装的方法。在下面的示例中，我将它们列在类变量 _scale_methods 中。
def wrap_scale_methods(cls):
Base = cls.__base__
def factor_scale(f):
def wrapper(self, *args, **kwargs):
scaled = Base.__mul__(self, FACTOR)
result = f(scaled, *args, **kwargs)
if isinstance(result, Base):
result = type(self)(result/FACTOR)
return result
return wrapper
for methodname in cls._scale_methods:
setattr(cls, methodname, factor_scale(getattr(Base, methodname)))
return cls
@wrap_scale_methods
class FactorComplex(complex):
_scale_methods = '__str__ __mul__ __div__ __add__ __sub__'.split()
def __repr__(self):
return '%s(%s)' % (type(self).__name__, complex.__repr__(self)[1:-1])
