[Twisted-Python] twisted.positioning: status report and request for comments/feedback

Glyph Lefkowitz glyph at twistedmatrix.com
Thu Jul 30 10:13:54 EDT 2009

On Thu, Jul 30, 2009 at 8:26 AM, Laurens Van Houtven <lvh at laurensvh.be>wrote:

> On Thu, Jul 30, 2009 at 3:01 AM, Glyph Lefkowitz<glyph at twistedmatrix.com>
> wrote:
>  > I've attached a sketch
> Extremely helpful, thank you.

You're welcome.

> To be honest, it
> still looks kind of wonky that a LineReceiver (well, a subclass)
> delegates to a receiver, but maybe that's just my inexperience showing
> :-)

Does it also bother you that 'dataReceived' delegates to 'lineReceived'? :)

What exactly would those
> startReceivingNMEA/stopReceivingNMEA/startReceivingPositions/stopReceivingPositions
> do? I don't think there's any setup to be done, so I guess that I
> should just have an instance attribute on the appropriate class that
> is set by startFoo/stopFoo. If it's false, callbacks don't fire.
> Right?

You don't need to do anything at all in these callbacks.  The important
point is to provide them, so that applications which, for example, wish to
show a little "GPS active" icon will know when data starts and stops
arriving.  Also important so that an application can re-connect or
re-initialize the device or whatever, without hooking implementing multiple
interfaces and hooking in at multiple levels.

Given that data for positioning may come from a variety of sources it's
important to have a positioning-specific method that marks the start and
stop, rather than depending on connectionMade or similar.  One could for
example imagine a hypothetical HTTP-polling-based positioning provider which
would have a connectionMade for every sentence of data, but that wouldn't
represent a start and a stop at the positioning level.  start would simply
be called before the first position, and stop would be called after a
timeout or after certain varieties of HTTP error.
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