[PyQt] QTcpSocket connections

[Jorge Tornero - Listas]

Hello all,

Thank you for your answers.

Finally I've managed to make it work, but a strange behavior (at least 
for newbies like me) arose. When I use readyRead signal, I can't get 
more than a single byte to read.

Finally I've had to do this: Make a sort of loop in reading() function 
to read one by one and append to a string. I don't get any results with 
readline and friends, I guess because the device I am communicating with 
uses \r instead of \n as line end. So read(1) or readAll() do the trick.

http://pastebin.com/zQ2iFRie


Again, thank you very much for your help

Jorge Tornero




And it works. Maybe the problem is related to the fact that my scale 
uses just \r (chr 13) as line ending character, so readLine and folks 
don't work as expected.


El 23/07/13 07:43, Phil Thompson escribió:
> On Tue, 23 Jul 2013 00:20:48 +0200, Jorge Tornero <jtorlistas at gmail.com>
> wrote:
>> Hello again, and thanks for your answer:
>>
>> Well I tried what you suggested (I guess) but got no luck. I know that I
> am
>> able to send the data but can't receive anything... seems that readAll
> or
>> read....() don't work at all
>>
>> I've drop some lines on pastebin
>> http://pastebin.com/mpYC0pPt
>>
>>
>> with an tiny application where the problem is shown
>>
>> I hope someone can put some light on this... Thank you very much
> readAll() returns all data that has been read from the device since the
> last read. It won't wait for data to arrive because it doesn't know how
> much is expected. Use the readyRead() signal.
>
> Phil
>
>
>> 2013/7/22 Phil Thompson <phil at riverbankcomputing.com>
>>
>>> On Mon, 22 Jul 2013 16:31:55 +0200, Jorge Tornero - Listas
>>> <jtorlistas at gmail.com> wrote:
>>>> Hello everybody,
>>>>
>>>> I'm trying to share a digital scale through the network, making it
> able
>>>> to receive tare/send weight commands.
>>>> The scale is connected to a remote computer (a raspberry pi, by the
>>>> way)
>>>> with a serial converter an the raspi is executing remserial, thus
> makin
>>>> avalilable the serial port to the network through port 23000.
>>>>
>>>> Because I am making my application with PyQt4, I have chosen to use
>>>> QTcpSocket to do the communications between the computers. It is
> pretty
>>>> easy and I am able to get what i want (sending command and receiving
>>>> weights) just by:
>>>>
>>>> soc=QtNetwork.QTcpSocket()
>>>>
>>>>
>>>> soc.connectToHost('174.33.22.11',23000)
>>>>
>>>> soc.writeData('01ST@')
>>>> print soc.readAll()
>>>> soc.disconnectFromHost()
>>>>
>>>>
>>>> And of course I get the weight and I am able to repeat the cycle
>>>> connect-poll-receive-disonnect
>>>>
>>>> The problem is whe I put that into a function like:
>>>>
>>>> def captura():
>>>>
>>>>     soc=QtNetwork.QTcpSocket(app)
>>>>     comandoCaptura=chr(6)+'01S@'+chr(13)
>>>>     soc.connectToHost('172.23.2.25',23000)
>>>>     soc.writeData(comandoCaptura)
>>>>     a=soc.readAll()
>>>>     print a
>>>>     soc.disconnectFromHost()
>>>>     return a
>>>>
>>>>
>>>> Ther is no wai to make it works. I guess is a basic python issue, but
>>>> can anyone help?
>>> QTcpSocket is asynchronous, so you need an event loop. After calling
>>> connectToHost() you shouldn't try to read or write until the
> connected()
>>> signal has been emitted.
>>>
>>> Phil
>>>

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