Re: [python-win32] Python - connexion to serial port

[Tim Roberts]

Schoeni, Yann wrote:
>  
>
> « is the Python script persistent (is it running continuously in the
> background) or launched for each transaction? »
>
>  
>
> -   Currently, the script is launched for each transaction. As I
> understand your proposition, when the web page is open,
>
>    an ajax request should call a python script which open a thread
> between the machine and the serial peripheral, right ?
>

I'm still not clear what problems you are seeing with the
open/send/close paradigm.  What leads you to make a change?  The
open/send/close model is usually easier to handle, because the process
starts with a clean slate every time.  Once you go to a long-running
process, you have more things to keep track of.

Dennis is not necessarily proposing a new thread.  Consider, for
example, a server application using one of the frameworks, like Flask or
CherryPy or Django.  Such an application gets launched once, and sits
idle waiting for to send it things to do.  When it gets a request
(either from a socket or routed from Apache), it reads input, takes
action, sends output, then waits for more things to do.

Dennis' proposal is the same.  Have a Python script running
continuously.  When an Ajax request comes in (either from a socket or
from Apache), you communicate with the serial port and send your
response.  The serial port can remain open, because the application does
not close.

But I'm not convinced that complexity is needed.  The open/send/close
model should work just fine.


> -   Even if I find a way to open a thread with the serial port or
> to keep it open with a loop, is it possible to send it orders ?

Why wouldn't it?

-- 
Tim Roberts, t...@probo.com
Providenza & Boekelheide, Inc.

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Re: [python-win32] Python - connexion to serial port

[Paul.Koning]

> On Jan 11, 2018, at 11:36 AM, Dennis Lee Bieber  wrote:
> 
> On Thu, 11 Jan 2018 15:12:33 +, "Schoeni, Yann"
>  declaimed the following:
> 
>> I've a web application which needs to send data to a serial port. The 
>> webserver uses ajax to send data to a python script.
>> 
>> The Python script uses the serial module to open, send data, and close the 
>> serial port.
>> 
>> Is there a way to keep the serial port open ?
>> 
>> Because for now, I open/close it between each transaction and I need to be 
>> 100% sure the data package will be send .. which is not the case with my 
>> actual python script.

I'd add one observation: while you can be reasonably sure that data is sent if 
you ask the serial port to send it, that does NOT mean it will be received.  I 
suspect what is actually needed is a guarantee that the data is received.

A serial port does not offer that guarantee.  If the hardware is clean, it only 
offers a high probability.  If you want guarantees, you need a data checking 
and acknowledgement protocol, like DDCMP or TCP or DECnet.

paul

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Re: [python-win32] Python - connexion to serial port

[Schoeni, Yann]

Hey,



« is the Python script persistent (is it running continuously in the 
background) or launched for each transaction? »



-   Currently, the script is launched for each transaction. As I understand 
your proposition, when the web page is open,

   an ajax request should call a python script which open a thread between 
the machine and the serial peripheral, right ?



-   is it hard to code this kind of mechanism ? To be honest I've never 
worked with thread.



-   Even if I find a way to open a thread with the serial port or to keep 
it open with a loop, is it possible to send it orders ?


-   Is there someone who has already experience that kind of situation ?



Thank you for your answer.



Best wishes



Yann Schoeni

Municipalité de Moutier

Apprenti informaticien

Tél. +41 (0)32 494 11 69

Mob. +41 (0)79 827 30 86

E-mail yann.scho...@moutier.ch



-Message d'origine-

De : python-win32 
[mailto:python-win32-bounces+yann.schoeni=moutier...@python.org] De la part de 
Dennis Lee Bieber

Envoyé : jeudi, 11 janvier 2018 17:37

À : python-win32@python.org

Objet : Re: [python-win32] Python - connexion to serial port



On Thu, 11 Jan 2018 15:12:33 +, "Schoeni, Yann"

 declaimed the following:



>I've a web application which needs to send data to a serial port. The 
>webserver uses ajax to send data to a python script.

>

>The Python script uses the serial module to open, send data, and close the 
>serial port.

>

>Is there a way to keep the serial port open ?

>

>Because for now, I open/close it between each transaction and I need to be 
>100% sure the data package will be send .. which is not the case with my 
>actual python script.

>



First question: is the Python script persistent (is it running 
continuously in the background) or launched for each transaction?



For the former (continuous background) why can't you just open the 
port at the start of the process and leave it open; looping around just the 
transaction processing.



If the latter -- not really, as even if you didn't close the port, 
the script shutdown will. You would have to create a separate long-term process 
(not thread, as the thread would have to exit to let the Python script 
terminate in this scenario). Your Python script would have to transfer the data 
to be written to the long-term process and let it do the serial port handling.



I'm not certain how you'd handle the transfer... All the IPC 
examples in the multiprocessing library are predicated upon one Python script 
starting the other process(es) and passing identifiers for the IPC channels 
(queue, pipes) to the subprocess. Perhaps by having the long-term process 
create a multiprocessing.manager instance configured for "remote connection" 
(even if the connection is localhost for both ends), and which the transaction 
script then attaches.

--

Wulfraed Dennis Lee Bieber AF6VN

wlfr...@ix.netcom.comHTTP://wlfraed.home.netcom.com/



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