一些黑魔法可以帮助您实现目标：
operators = ["add", "mul"]
class OperatorHackiness(object):
"""
Use this base class if you want your object
to intercept __add__, __iadd__, __radd__, __mul__ etc.
using __getattr__.
__getattr__ will called at most _once_ during the
lifetime of the object, as the result is cached!
"""
def __init__(self):
# create a instance-local base class which we can
# manipulate to our needs
self.__class__ = self.Meta = type('tmp', (self.__class__,), {})
# add operator methods dynamically, because we are damn lazy.
# This loop is however only called once in the whole program
# (when the module is loaded)
def create_operator(name):
def dynamic_operator(self, *args):
# call getattr to allow interception
# by user
func = self.__getattr__(name)
# save the result in the temporary
# base class to avoid calling getattr twice
setattr(self.Meta, name, func)
# use provided function to calculate result
return func(self, *args)
return dynamic_operator
for op in operators:
for name in ["__%s__" % op, "__r%s__" % op, "__i%s__" % op]:
setattr(OperatorHackiness, name, create_operator(name))
# Example user class
class Test(OperatorHackiness):
def __init__(self, x):
super(Test, self).__init__()
self.x = x
def __getattr__(self, attr):
print "__getattr__(%s)" % attr
if attr == "__add__":
return lambda a, b: a.x + b.x
elif attr == "__iadd__":
def iadd(self, other):
self.x += other.x
return self
return iadd
elif attr == "__mul__":
return lambda a, b: a.x * b.x
else:
raise AttributeError
## Some test code:
a = Test(3)
b = Test(4)
# let's test addition
print(a + b) # this first call to __add__ will trigger
# a __getattr__ call
print(a + b) # this second call will not!
# same for multiplication
print(a * b)
print(a * b)
# inplace addition (getattr is also only called once)
a += b
a += b
print(a.x) # yay!
__getattr__(__add__)
7
7
__getattr__(__mul__)
12
12
__getattr__(__iadd__)
11
现在，您可以通过继承我的OperatorHackiness基类来使用第二个代码示例。您甚至可以获得额外的好处：__getattr__每个实例和每个运算符仅被调用一次，并且缓存不涉及额外的递归层。我们在此规避了方法调用比方法查找慢的问题（正如Paul Hankin正确注意到的那样）。
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