Python中描述的动态文档字符串(Creating dynamic docstrings in P

我试图动态生成一些类定义（用于包装C ++扩展）。下面的描述，除了工作，当我尝试访问的文档字符串的使用领域的帮助（）的罚款，它提供了默认文档的描述，而不是场它的自我。然而，当我这样做帮助（类名），它检索传递给描述符的文档字符串：

class FieldDescriptor(object):
    def __init__(self, name, doc='No documentation available.'):
        self.name = name
        self.__doc__ = doc

    def __get__(self, obj, dtype=None):
        if obj is None and dtype is not None:
            print 'Doc is:', self.__doc__
            return self
        return obj.get_field(self.name)

    def __set__(self, obj, value):
        obj.set_field(self.name, value)

class TestClass(object):
    def __init__(self):
        self.fdict = {'a': None, 'b': None}

    def get_field(self, name):
        return self.fdict[name]

    def set_field(self, name, value):
        self.fdict[name] = value

fields = ['a', 'b']
def define_class(class_name, baseclass):
    class_obj = type(class_name, (baseclass,), {})
    for field in fields:
        setattr(class_obj, field, FieldDescriptor(field, doc='field %s in class %s' % (field, class_name)))
    globals()[class_name] = class_obj


if __name__ == '__main__':
    define_class('DerivedClass', TestClass)
    help(DerivedClass.a)
    help(DerivedClass)
    v = DerivedClass()
    help(v.a)

“蟒蛇test.py”打印：

Doc is: field a in class DerivedClass
Help on FieldDescriptor in module __main__ object:

class FieldDescriptor(__builtin__.object)
 |  Methods defined here:
 |  
 |  __get__(self, obj, dtype=None)
 |  
 |  __init__(self, name, doc='No documentation available.')
 |  
 |  __set__(self, obj, value)
 |  
 |  ----------------------------------------------------------------------
 |  Data descriptors defined here:
 |  
 |  __dict__
 |      dictionary for instance variables (if defined)
 |  
 |  __weakref__
 |      list of weak references to the object (if defined)

Doc is: field a in class DerivedClass
Doc is: field b in class DerivedClass
Help on class DerivedClass in module __main__:

class DerivedClass(TestClass)
 |  Method resolution order:
 |      DerivedClass
 |      TestClass
 |      __builtin__.object
 |  
 |  Data descriptors defined here:
 |  
 |  a
 |      field a in class DerivedClass
 |  
 |  b
 |      field b in class DerivedClass
 |  
 |  ----------------------------------------------------------------------
 |  Methods inherited from TestClass:
 |  
 |  __init__(self)
 |  
 |  get_field(self, name)
 |  
 |  set_field(self, name, value)
 |  
 |  ----------------------------------------------------------------------
 |  Data descriptors inherited from TestClass:
 |  
 |  __dict__
 |      dictionary for instance variables (if defined)
 |  
 |  __weakref__
 |      list of weak references to the object (if defined)

Help on NoneType object:

class NoneType(object)
 |  Methods defined here:
 |  
 |  __hash__(...)
 |      x.__hash__()  hash(x)
 |  
 |  __repr__(...)
 |      x.__repr__()  repr(x)

任何想法，如何能够获得descriptor.__doc__的help(class.field) 而且是有办法绕过这一点，有一些像在具有存储在描述符doc字符串代替DOC getter函数？

喜欢：

class FieldDescriptor(object):
    def __init__(self, name, doc='No documentation available.'):
        self.name = name
        self.__doc__ = doc

    def __get__(self, obj, dtype=None):
        if obj is None and dtype is not None:
            print 'Doc is:', self.__doc__
            return self
        return obj.get_field(self.name)

    def __set__(self, obj, value):
        obj.set_field(self.name, value)

    # This is what I'd like to have
    def __doc__(self, obj, dtype):
       return dtype.generate_docstring(self.name)

UPDATE：其实我开始用这个定义的__get__ ：

def __get__(self, obj, dtype=None):
    return obj.get_field(self.name)

这样做的问题是，当我说：

help(DerivedClass.a)

Python中抛出一个异常，表明我是想叫None.get_field 。因此help()被调用__get__与方法obj=None和dtype=DerivedClass 。这就是为什么我决定当的obj =无返回FieldDescriptor实例和D型！=无。我的印象是help(xyz)试图显示xyz.__doc__ 。由该逻辑，如果__get__返回descriptor_instance ，然后descriptor_instance.__doc__应由帮助（），它是整个类[的情况下打印help(DerivedClass) ]，但没有为单个字段[ help(DerivedClass.a) ] 。