Hello all, my first post here - only been using Twisted for about a
month and am also a relative newcomer to Python but have been coding
professionally for 20+ years. I was attracted to Twisted and Python
for a particular project purely because after research it seemed to be
the best tool for the job, and have actually been enjoying both Python
and Twisted much more than I ever thought I would.
The project I am coding towards is creating a sensor data collection
gateway. First iteration needs are simply pulling data from ModBus TCP
slave PLCs and writing it to a MySQL database, but goals beyond that
are making the source of the data and its destination(s) very
flexible(pluggable). Therefore I am trying to create a good clean
architecture from the outset so as I iterate forwards I don't finish
up having to take too many steps backwards before heading forwards.
I am using pymodbus to pull the data which works well for my devices,
has a twisted async API, and have created more than a few prototypes
that demonstrate all works as I expect. Where I am a bit stalled is
getting to grips with a good architecture that fulfills my needs - my
intention is that the application that meets my first goal will be a
twistd plugin.
The new ClientService class seems like it will fit my needs very
closely but I am struggling with how to handle the reconnections... I
have been using the whenConnected() method to grab the Protocol for
the initial connection and then use a method of this to poll the
connected slave. When the connection is lost I get an errback from
this method's deferred which I use as a signal to abandon the Protocol
and call whenConnected() again... at this point I have an issue though
as the returned deferred immediately gives me a callback with the same
Protocol which has just lost its connection, and thus loop...
Before I got on this mailing list I posted this Q to stackoverflow
with some example code:
http://stackoverflow.com/q/37061807/3448214
but no solution or much attention there yet.
As I say there, I realize I have probably just made a bad pattern
choice for how to use this API, but I have not been able to work out a
better choice which seems clean and fits my needs/understanding well.
I have tried deriving my own Protocol/Factory and handling the polling
there but this seems to get really messy once I start to add code to
get the collected data to a destination at that level, involving
giving the Protocol too much knowledge of how the data is to be
handled.
Any advice, good patterns, or pointers to other projects which do
something similar is appreciated,
Cheers
/dan
--
Daniel Sutcliffe <dan...@gmail.com>
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