1.Return 异常

class Return(Exception):

    """Special exception to return a value from a `coroutine`.

    If this exception is raised, its value argument is used as the

    result of the coroutine::

        @gen.coroutine

        def fetch_json(url):             response = yield AsyncHTTPClient().fetch(url)             raise gen.Return(json_decode(response.body))

    In Python 3.3, this exception is no longer necessary: the ``return``

    statement can be used directly to return a value (previously     ``yield`` and ``return`` with a value could not be combined in the     same function).

    By analogy with the return statement, the value argument is optional,

    but it is never necessary to ``raise gen.Return()``.  The ``return``     statement can be used with no arguments instead.     """     def __init__(self, value=None):         super(Return, self).__init__()                 self.value = value         # Cython recognizes subclasses of StopIteration with a .args tuple.         self.args = (value,)

 

2.gen.corountine装饰器中捕获异常

        try:             result = func(*args, **kwargs)         except (Return, StopIteration) as e:        #捕获了Return异常             result = _value_from_stopiteration(e)         except Exception:             future.set_exc_info(sys.exc_info())             return future

3.使用方式，参考1

@gen.coroutine

        def fetch_json(url):             response = yield AsyncHTTPClient().fetch(url)             raise gen.Return(json_decode(response.body))

 

        else:    

            。。