Error: Types.coroutine() Expects A Callable

I have the following class: from tornado import gen class VertexSync(Vertex): @wait_till_complete @gen.coroutine @classmethod def find_by_value(cls, *args, **kwarg

Solution 1:

The problem is that classmethod does... interesting things. Once the class definition has finished you have a nice callable method on the class, but during the definition you have a classmethod object, which isn't callable:

>>> a = classmethod(lambda self: None)
>>> a
<classmethod object at 0x10b46b390>
>>> callable(a)
False
>>> a()
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'classmethod' object is not callable

The simplest fix is to re-order the decorators, so that rather than trying to turn a classmethod into a coroutine:

@gen.coroutine
@classmethod
def thing(...):
    ...

you are trying to turn a coroutine into a classmethod:

@classmethod
@gen.coroutine
def thing(...):
    ...

Note that the decorators are applied "inside out", see e.g. Decorator execution order