Question

我想创建一个代理类，它包装int以进行线程安全访问。与内置类型相比，代理类是可变的，因此它可以就地递增。现在，我想将该类用作外部的普通整数。通常，Python的__getattr__可以很容易地将属性访问转发到内部对象：

class Proxy:

    def __init__(self, initial=0):
        self._lock = threading.Lock()
        self._value = initial

    def increment(self):
        with self._lock:
            self._value += 1

    def __getattr__(self, name):
        return getattr(self._value, name)

然而，__getattr__ does not get triggered for magic methods类似于__add__，__rtruediv__等我需要让代理行为像整数一样。有没有办法自动生成这些方法，或者将它们转发到包装的整数对象？

Answer 1

@VPfB中由comments链接的博客文章对内置类型的代理dunder方法有一个更通用和彻底的解决方案，但这是一个简化而相当野蛮的例子。我希望它有助于理解如何创建这样的转发方法。

import threading
import numbers


def _proxy_slotted(name):
    def _proxy_method(self, *args, **kwgs):
        return getattr(self._value, name)(*args, **kwgs)
    # Not a proper qualname, but oh well
    _proxy_method.__name__ = _proxy_method.__qualname__ = name
    return _proxy_method

# The list of abstract methods of numbers.Integral
_integral_methods = """
    __abs__ __add__ __and__ __ceil__ __eq__ __floor__
    __floordiv__ __int__ __invert__ __le__ __lshift__
    __lt__ __mod__ __mul__ __neg__ __or__ __pos__ __pow__
    __radd__ __rand__ __rfloordiv__ __rlshift__ __rmod__
    __rmul__ __ror__ __round__ __rpow__ __rrshift__
    __rshift__ __rtruediv__ __rxor__ __truediv__ __trunc__
    __xor__""".split()

# The dunder, aka magic methods
_Magic = type('_Magic', (),
              {name: _proxy_slotted(name)
               for name in _integral_methods})


class IntProxy(_Magic, numbers.Integral):
    """
    >>> res = IntProxy(1) + 1
    >>> print(type(res), res)
    <class 'int'> 2
    >>> print(IntProxy(2) / 3)
    0.6666666666666666
    """

    def __init__(self, initial=0, Lock=threading.Lock):
        self._lock = Lock()
        self._value = initial

    def increment(self):
        with self._lock:
            self._value += 1

    def __getattr__(self, name):
        return getattr(self._value, name)

如何使代理对象的行为与它包装的整数相似？

1 个答案: