"yielded unknown object None" Error on connect

[jslootweg]

I was just trying out the demo's I get the following error in both when the code attempts to open a connection

File "/Library/Python/2.7/site-packages/tornado_mysql/connections.py", line 820, in connect
    2003, "Can't connect to MySQL server on %r (%s)" % (self.host, e))
tornado_mysql.err.OperationalError: (2003, "Can't connect to MySQL server on 'databaseserver' (yielded unknown object None)")

I am running on Yosemite with Python 2.7. MySQL server is running on a remote VM. I can confirm this machine will accept remote connections, I have tested this using the blocking MySQL tornado library.

[methane]

Python 2.7 and OperationalError hides real traceback.
Could you try again with Python 3.4?

Or could you try with this modification to connections.py?

-            if isinstance(e, err.MySQLError):
-                raise
-            raise OperationalError(
-                2003, "Can't connect to MySQL server on %r (%s)" % (self.host, e))
+            raise

[jslootweg]

OK this is the stack trace which results from making that mod.

Traceback (most recent call last):
  File "/Users/james/Desktop/pymysqltest/example.py", line 29, in <module>
    ioloop.IOLoop.current().run_sync(main)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/ioloop.py", line 365, in run_sync
    return future_cell[0].result()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/concurrent.py", line 129, in result
    raise_exc_info(self.__exc_info)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/stack_context.py", line 239, in wrapped
    callback(*args, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/gen.py", line 551, in inner
    self.set_result(key, result)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/gen.py", line 480, in set_result
    self.run()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/gen.py", line 508, in run
    yielded = self.gen.throw(*exc_info)
  File "/Users/james/Desktop/pymysqltest/example.py", line 18, in main
    conn = yield tornado_mysql.connect(host='databaseserver', port=3306, user='redacted', passwd='redacted', db='redacted')
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/gen.py", line 500, in run
    next = self.yield_point.get_result()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/gen.py", line 402, in get_result
    return self.runner.pop_result(self.key).result()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/concurrent.py", line 129, in result
    raise_exc_info(self.__exc_info)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/stack_context.py", line 263, in _nested
    yield vars
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/stack_context.py", line 236, in wrapped
    callback(*args, **kwargs)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/gen.py", line 551, in inner
    self.set_result(key, result)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/gen.py", line 480, in set_result
    self.run()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/gen.py", line 508, in run
    yielded = self.gen.throw(*exc_info)
  File "/Library/Python/2.7/site-packages/tornado_mysql/__init__.py", line 88, in connect
    yield conn.connect()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/gen.py", line 500, in run
    next = self.yield_point.get_result()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/gen.py", line 402, in get_result
    return self.runner.pop_result(self.key).result()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/concurrent.py", line 129, in result
    raise_exc_info(self.__exc_info)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/gen.py", line 228, in wrapper
    runner.run()
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/tornado/gen.py", line 508, in run
    yielded = self.gen.throw(*exc_info)
  File "/Library/Python/2.7/site-packages/tornado_mysql/connections.py", line 790, in connect
    yield stream.connect(addr)
tornado.gen.BadYieldError: yielded unknown object None

Using the debugger I can see the stream.connect calls into the Tornado iostream.py and goes into

    try:
        self.socket.connect(address)
    except socket.error as e:
        # In non-blocking mode we expect connect() to raise an
        # exception with EINPROGRESS or EWOULDBLOCK.
        #
        # On freebsd, other errors such as ECONNREFUSED may be
        # returned immediately when attempting to connect to
        # localhost, so handle them the same way as an error
        # reported later in _handle_connect.
        if e.args[0] not in (errno.EINPROGRESS, errno.EWOULDBLOCK):
            gen_log.warning("Connect error on fd %d: %s",
                            self.socket.fileno(), e)
            self.close(exc_info=True)
            return
    self._connect_callback = stack_context.wrap(callback)
    self._add_io_state(self.io_loop.WRITE)

and the exception argument is EINPROGRESS as expected.

I did notice that the argument callback is None. Therefore the yield would correctly 'yield' None. (If my understanding is correct?)

[methane]

http://www.tornadoweb.org/en/stable/iostream.html#tornado.iostream.IOStream.connect

Changed in version 4.0: If no callback is given, returns a Future.

Maybe your tornado is too old.
Anyway, I don't use my time for this project anymore.