Use of Python metaclass I - getattr for static/class variable

使用元类控制类变量访问

最新推荐文章于 2025-07-05 14:08:01 发布

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本文介绍了一种使用Python元类来控制类或静态变量访问的方法。通过重写`__getattr__`方法，可以自定义如何获取这些变量，从而实现更加灵活的类属性管理。

In my previous post, I disussesed with the reader the concept of metaclass and its internals. this post is inspired from this post from stackoverflow.

In this post, I will visit one of the use of meta class so so that we can control the access to the class/static variable through the use of __getattr__ call

class GetAttrOnStaticClassVariableMetaclass(type):
    '''
    This is a use case that uses the Metaclass to create a classes that you can access the Class/Static variable
    via call to __getattr__
    '''
    
    # due to some stupid reaon, I could not use cls as the first parameter, I have to use the 
    # self as the first parameter, which is really dume
    def _foo_func(self):
        return 'foo!'
    def _bar_func(self):
        return 'bar!'
    def __getattr__(self, key):
        if (key == 'Foo'):
            return self._foo_func()
        elif (key == 'Bar'):
            return self._bar_func()
        raise AttributeError(key)
    def __str__(self):
        return 'custom str for %s' % (self.__name__,)

and the following is the unit test case to show how to use it .

import unittest
from MetaClass.GetAttrOnStaticClassVariableMetaclass import GetAttrOnStaticClassVariableMetaclass


class Test(unittest.TestCase):


    def test_getAttrOnStaticClassVariable_should_access_static_variables(self):
        class Foo:
            __metaclass__ = GetAttrOnStaticClassVariableMetaclass
        self.assertEqual(True, hasattr(Foo, "Foo"), "Unable to get Static Class variable")
        self.assertEqual(True, hasattr(Foo, "Bar"), "Unable to get Static Class variable")
        self.assertEqual('foo!', Foo.Foo, "Unable to get Static Class variable")
        self.assertEqual('bar!', Foo.Bar, "Unable to get Static Class variable")
        
if __name__ == "__main__":
    #import sys;sys.argv = ['', 'Test.testGetAttrOnStaticClassVariable_should_access_static_variables']
    unittest.main()