我可以从只能由“工厂"创建的类派生吗? [英] Can I derive from a class that can only be created by a "factory"?

问题描述

假设我使用的库实现了一个类

Suppose that a library I'm using implements a class

class Base(object):
    def __init__(self, private_API_args):
        ...

它只能通过实例化

def factory(public_API_args):
    """
    Returns a Base object
    """
    ...

我想通过添加几个方法来扩展 Base 类:

I'd like to extend the Base class by adding a couple of methods to it:

class Derived(Base):
    def foo(self):
        ...
    def bar(self):
        ...

是否可以在不调用私有 API 的情况下初始化 Derived ?

Is it possible to initialize Derived without calling the private API though?

换句话说，我应该用什么替代 factory 函数?

In other words, what should be my replacement for the factory function?

推荐答案

如果您没有任何访问私有 API 的权限，您可以执行以下操作:

If you do not have any access to the private API, you can do the following thing:

class Base(object):
    def __init__(self, private_API_args):
        ...


def factory(public_API_args):
    """ Returns a Base object """
    # Create base object with all private API methods
    return base_object


class Derived(object):
    def __init__(self, public_API_args):
        # Get indirect access to private API method of the Base object class
        self.base_object = factory(public_API_args)

    def foo(self):
        ...
    def bar(self):
        ...

现在在主脚本中:

#!/usr/bin/python3

# create the derivate object with public API args
derived_object = Derived(public_API_args)

# to call private API methods
derived_object.base_object.method()

# to call your method from the same object
derived_object.foo()
derived_object.bar()

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