python:概括委托(delegate)方法

Question

我有一个包含一个或多个数字元素的类。

class Foo:
    # ... other methods ...
    def _update(self, f):
        # ... returns a new Foo() object based on transforming
        #     one or more data members with a function f()
    def __add__(self, k):
        return self._update(lambda x: x.__add__(k))
    def __radd__(self, k):
        return self._update(lambda x: x.__radd__(k))
    def __sub__(self, k):
        return self._update(lambda x: x.__sub__(k))
    def __rsub__(self, k):
        return self._update(lambda x: x.__rsub__(k))
    def __mul__(self, k):
        return self._update(lambda x: x.__mul__(k))
    def __rmul__(self, k):
        return self._update(lambda x: x.__rmul__(k))
    def __div__(self, k):
        return self._update(lambda x: x.__div__(k))
    def __rdiv__(self, k):
        return self._update(lambda x: x.__rdiv__(k))
    # I want to add other numeric methods also

有没有什么方法可以将此概括为所有 numeric methods ，而不必为每个人都这样做？

我只想委托(delegate)数字方法列表中的任何方法。

Answer 1

您想使用 operator module在这里，连同一个(简短的)二进制数字运算符名称列表，为了紧凑而没有下划线:

import operator 

numeric_ops = 'add div floordiv mod mul pow sub truediv'.split()

def delegated_arithmetic(handler):
    def add_op_method(op, cls):
        op_func = getattr(operator, op)
        def delegated_op(self, k):
            getattr(self, handler)(lambda x: op_func(x, k))
        setattr(cls, '__{}__'.format(op), delegated_op)

    def add_reflected_op_method(op, cls):
        op_func = getattr(operator, op)
        def delegated_op(self, k):
            getattr(self, handler)(lambda x: op_func(k, x))
        setattr(cls, '__r{}__'.format(op), delegated_op)

    def decorator(cls):
        for op in numeric_ops:
            add_op_method(op, cls)
            add_reflected_op_method(op, cls) # reverted operation
            add_op_method('i' + op, cls)     # in-place operation
        return cls

    return decorator

现在装饰你的类:

@delegated_arithmetic('_update')
class Foo:
    # ... other methods ...
    def _update(self, f):
        # ... returns a new Foo() object based on transforming
        #     one or more data members with a function f()

装饰器采用您想将调用委托(delegate)给的名称，以使其更通用一些。

演示:

>>> @delegated_arithmetic('_update')
... class Foo(object):
...     def _update(self, f):
...         print 'Update called with {}'.format(f)
...         print f(10)
... 
>>> foo = Foo()
>>> foo + 10
Update called with <function <lambda> at 0x107086410>
20
>>> foo - 10
Update called with <function <lambda> at 0x107086410>
0
>>> 10 + foo
Update called with <function <lambda> at 0x107086410>
20
>>> 10 - foo
Update called with <function <lambda> at 0x107086410>
0