Python Docstrings в подклассах

Question

Я создаю класс в Python, который затем добавляют некоторые вложенные классы, добавленные с помощью SetAttr ().

class T( object ):
    def __init__( self ):
        cDict = {}
        cDict['__doc__'] = 'Inner class doc string'
        setattr( self, 'C', type('C', (), cDict ) )

.

Тем не менее, Shaling Help (T) не включает в себя и информацию о C. Создание T, а затем A C внутри нее работает нормально.

Делать это традиционный путь отлично работает:

class T2( object ): 
    class C2( object ):
        __doc__ = 'Inner class doc string'

.

Помощь вызывающей связи (T2) Отображает информацию о C2.

Может кто-нибудь может пролить свет на то, что здесь происходит?Спасибо.

Answer 1

The two snippets you showed are not equivalent.

This:

class T( object ):
    def __init__( self ):
        cDict = {}
        cDict['__doc__'] = 'Inner class doc string'
        setattr( self, 'C', type('C', (), cDict ) )

will set a C attribute on each T instance:

>>> T.C
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: type object 'T' has no attribute 'C'
>>> t = T()
>>> t.C
<class '__main__.C'>

This is because you placed the setattr inside __init__.

While this:

class T2( object ): 
    class C2( object ):
        __doc__ = 'Inner class doc string'

will add an attribute on T2 itself:

>>> T2.C2
<class '__main__.C2'>

Answer 2

help operates on classes and types, rather than objects. However, your T only has the member C in objects (when __init__ has been run). So help can't detect it.

Your T2 also contains C2 in the class itself, so help detects it and displays the correct information.

Answer 3

The first way causes C to be an instance attribute of each T object.

The second way causes C to be a class attribute of the T class.

help(T) provides help on the T class (well, the object that the name T refers to, which in this case is a class). It can't know anything about any given instance of T, even if it's true for every instance (and it might not be, anyway; later code could do my_T = T(); del my_T.C).