python - Python中如何进行封装？

Question

这是怎么回事？从客观和功能的角度来看？

import sys

class EncapsulationClass(object):

  def __init__(self):
    self.privates = ["__dict__", "privates", "protected", "a"]
    self.protected = ["b"]

    print self.privates

    self.a = 1
    self.b = 2
    self.c = 3
    pass

  def __getattribute__(self, name):
    if sys._getframe(1).f_code.co_argcount == 0:
      if name in self.privates:
        raise Exception("Access to private attribute \"%s\" is not allowed" % name)
      else:
        return object.__getattribute__(self, name)
    else:
      return object.__getattribute__(self, name)

  def __setattr__(self, name, value):
    if sys._getframe(1).f_code.co_argcount == 0:
      if name in self.privates:
        raise Exception("Setting private attribute \"%s\" is not allowed" % name)
      elif name in self.protected:
        raise Exception("Setting protected attribute \"%s\" is not allowed" % name)
      else:
        return object.__setattr__(self, name, value)
    else:
      return object.__setattr__(self, name, value)


example = EncapsulationClass()

example.a = 10 # Exception: Setting private attribute "a" is not allowed
example.b = 10 # Exception: Setting protected attribute "b" is not allowed
example.c = 10 # example.c == 10

example.__dict__["privates"] # Exception: Setting protected attribute "b" is not allowed

这样做实际上有什么问题？

有没有更好的办法在Python中实现封装？

Answer 1

Python 具有封装性——您正在类里面使用它。

它没有的是访问控制，例如私有(private)和 protected 属性。但是，在 Python 中，有一种属性命名约定，通过在属性前加上一个或两个下划线来表示私有(private)属性，例如:

self._a
self.__a 

单个下划线向类的用户指示属性应被视为该类的私有(private)属性，不应直接访问。

双下划线表示相同，但​​是，Python 会稍微破坏属性名称以试图隐藏它。

class C(object):
    def __init__(self):
        self.a = 123    # OK to access directly
        self._a = 123   # should be considered private
        self.__a = 123  # considered private, name mangled

>>> c = C()
>>> c.a
123
>>> c._a
123
>>> c.__a
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'C' object has no attribute '__a'
>>> c._C__a
123

您可以在最后一个示例中看到名称从 __a 更改为 _C__a，尽管它仍然可以在类中作为 self.__a< 访问.