Start the session if you try and run code

[blink1073]

Prior to this change, trying to run m.version() without calling m.start() gave this unhelpful message:

/home/silvester/workspace/python-matlab-bridge/pymatbridge/pymatbridge.py in _response(self, **kwargs)
    221     def _response(self, **kwargs):
    222         req = json.dumps(kwargs, cls=PymatEncoder)
--> 223         self.socket.send_string(req)
    224         resp = self.socket.recv_string()
    225         return resp

AttributeError: 'NoneType' object has no attribute 'send_string'

Also allows you to use m = Matlab().start()

[arokem]

I wonder whether that's always the behavior you want. What if you intentionally stopped the Matlab process? One option is to raise an informative error instead of this one, and force users to call start themselves. Another is to raise a warning of some kind, to alert the user to the fact that this going to start matlab for them. What do you think?

[blink1073]

I think the warning is a good compromise, what do you think @isbadawi?

[isbadawi]

I'm not sure I see the value in auto-starting it -- explicit is better than implicit, etc. I'd prefer to just see an exception. But I don't really feel strongly either way.

Maybe just play with the API to make this less of a pain point? You could add a function that returns an already started session, since you often create and start a session at the same time anyway, or make start() return the session again instead of a boolean, so you could write pymatbridge.Matlab().start() in one step.

(Reminds me of a similar problem with Stopwatch in Guava: https://plus.google.com/+googleguava/posts/8XeVCd7iKxo).