Question

我想要的是以下内容：

lst = []

class Awesome:
  """This is my magical super class."""

  ...

class Inherits(Awesome):
  """Awesome does awesome stuff with Inherits."""
  name = "Stack"

class InheritsAgain(Awesome):
  name = "Overflow"

print(lst)
#: ['Stack', 'Overflow']

所以基本上，当定义类Inherits和InheritsAgain时，因为它们继承自Awesome，Awesome有一些元类魔法（或其他），即读取继承类中的属性name，并将其附加到lst。

我看过Python中的元类，但我不确定它是如何组合在一起的。

这在Python中可行吗？如果是的话，你会怎么做呢？

修改

让我们添加上面的例子，这样也可以：

class AndAgain(Awesome):
  name = "/root/path/<name>/<id>"

  def go():
    pass

我希望定义整个班级AndAgain，以便我可以检查name是否存在值"/root/path/<name>/<id>"，而函数go()也存在

Answer 1

lst = []

class AwesomeMeta(type):
    def __new__(metacls, cls, bases, classdict):
        if cls != 'Awesome':
            lst.append(cls)
        return super().__new__(metacls, cls, bases, classdict)

class Awesome(metaclass=AwesomeMeta):
  """This is my magical super class."""


class Stack(Awesome):
  """Awesome does awesome stuff with Inherits."""


class Overflow(Awesome):
    """More awesomely stuff!"""

print(lst)

要在课堂上展示：

lst = []

class AwesomeMeta(type):
    def __new__(metacls, cls, bases, classdict):
        if 'name' in classdict:
            lst.append(classdict['name'])
        return super().__new__(metacls, cls, bases, classdict)

class Awesome(metaclass=AwesomeMeta):
    """This is my magical super class."""


class Inherits(Awesome):
    """Awesome does awesome stuff with Inherits."""

    name = 'Stack'


class InheritsAgain(Awesome):
    """More awesomely stuff!"""

    name = 'Overflow'

class AndAgain(Awesome):
    name = "/root/path/<name>/<id>"

    def go():
        pass

print(lst)

Answer 2

可以使用元类

class AwesomeMeta(type):
    lst = []
    def __new__(metacls, cls, bases, classdict):
        if 'name' in classdict:
            metacls.lst.append(classdict['name'])
        return super(AwesomeMeta, metacls).__new__(metacls, cls, bases, classdict)

class Awesome(object):
    """This is my magical super class."""
    __metaclass__ = AwesomeMeta


class Inherits(Awesome):
    """Awesome does awesome stuff with Inherits."""
    name = 'Stack'


class InheritsAgain(Awesome):
    """More awesomely stuff!"""
    name = 'Overflow'

print InheritsAgain.lst, Inherits.lst, Awesome.lst

或者可以使用__subclasses__方法

print [i.name for i in Awesome.__subclasses__()]

或者可以使用类装饰器

lst = []
def cls_decorator(cls):
    lst.append(cls.name)
    return cls

@cls_decorator
class Awesome(object):
    """This is my magical super class."""
    name = 'Awesome'


@cls_decorator
class Inherits(Awesome):
    """Awesome does awesome stuff with Inherits."""
    name = 'Stack'


@cls_decorator
class InheritsAgain(Awesome):
    """More awesomely stuff!"""
    name = 'Overflow'

解决方案应该取决于你打算做什么

课程定义后自动做一些事情？

2 个答案: