在对象实例化期间动态加载实例方法

Question

我希望能够在对象实例化期间动态加载实例方法。根据我的设计，默认行为是在基类中编码的。然而,如果在对象安装过程中满足一定的条件，动态地用另一段代码更改此行为。这就是我这样做:

默认行为编码为first.py:

class First(object):
    def __init__(self, p):
        p = str(p)
        #The decision whether or not to perform default action is done
        #in the following try/except block. In reality this block 
        #is more complicated
        #and more checks are performed in order to assure proper work
        try: 
            strImport = "__import__('module%s')"%p
            e = eval(strImport, {}, {})
            if not hasattr(e, p):
                raise ImportError()
        except ImportError:
            e = None #default behaviour
        if e is not None:
            self.act = getattr(e, p)(p).act #special behaviour
        self.p = p
    def act(self):
        print 'Default behaviour'

import cPickle as pickle

if __name__ == '__main__':
    print 'first'
    first = First('f')
    first.act()
    pickle.dump(first, open('first.dump', 'w'))
    print 'third'
    third = First('Third')
    third.act()
    pickle.dump(third, open('third.dump', 'w'))

在上面的代码中，first和third都执行默认操作。我可以改变

添加moduleThird.py文件，修改third的行为

from temp import First
class Third(First):
    def __init__(self, p):
        p = 'Third *** %p'
        print 'third init'
        super(self.__class__, self).__init__(p)

    def act(self):
        super(self.__class__, self).act()
        print 'Third acted'

添加此文件后，third改变其行为。但是我不是由于以下错误，无法pickle生成的对象:

Traceback (most recent call last):
  File "C:temptemp.py", line 35, in <module>
    pickle.dump(fff, open('fff.dump', 'w'))
  File "C:Python26libcopy_reg.py", line 70, in _reduce_ex
    raise TypeError, "can't pickle %s objects" % base.__name__
TypeError: can't pickle instancemethod objects

很明显，动态加载方法Third.act导致了pickle的问题。为了获得可选择的对象(以及更优雅的代码)，我需要如何改变我的方法?

有没有更好的方法来实现我的目标?

Answer 1

如果您按照以下方式更改代码，那么它应该可以工作:

class First(object):
    def __init__(self, p):
        p = str(p)
        #The decision whether or not to perform default action is done
        #in the following try/except block. In reality this block 
        #is more complicated
        #and more checks are performed in order to assure proper work
        try: 
            strImport = "__import__('module%s')"%p
            print strImport
            e = eval(strImport, {}, {})
            if not hasattr(e, p):
                raise ImportError()
            self.override_obj = getattr(e, p)(p)
        except ImportError:
            e = None #default behaviour
            self.override_obj = None
        self.p = p
    def act(self):
        if self.override_obj:
            return self.override_obj.act()
        else:
            print 'Default behaviour'