Pyserial and pyQt

[Seth]

I have used pyserial in the past but this is my first experience with
pyQt. I am using the Python xy package for windows current but might
move to linux. I have a small device that is outputting a basic text
string. I want to be able to read this string(from the comm port) and
update a text box and eventually a graph in pyQt. I can't find any
documentation or tutorials on how to do this. If anyone can point me
in the right direction or give me some tips I would be grateful.

Thanks,
Seth

 

[David Boddie]

I have used pyserial in the past but this is my first experience with
pyQt. I am using the Python xy package for windows current but might
move to linux. I have a small device that is outputting a basic text
string. I want to be able to read this string(from the comm port) and
update a text box and eventually a graph in pyQt. I can't find any
documentation or tutorials on how to do this. If anyone can point me
in the right direction or give me some tips I would be grateful.

It seems that someone has already asked a similar question on Stack
Overflow, though perhaps you should start with a simpler solution
and look at more advanced ones later:

http://stackoverflow.com/questions/771988/pyqt4-and-pyserial

One starting point is this list of tutorials on the PyQt and PyKDE Wiki:

http://www.diotavelli.net/PyQtWiki/Tutorials

Later, when you want to draw graphs, you might find PyQwt useful:

http://pyqwt.sourceforge.net/

You may already be aware that there's also a mailing list for PyQt and
PyKDE:

http://www.riverbankcomputing.com/pipermail/pyqt/

Another way to get answers to questions is to join the #pyqt IRC channel
at freenode.net:

irc://irc.freenode.net/

David

 

[Seth]

It seems that someone has already asked a similar question on Stack
Overflow, though perhaps you should start with a simpler solution
and look at more advanced ones later:

 http://stackoverflow.com/questions/771988/pyqt4-and-pyserial

One starting point is this list of tutorials on the PyQt and PyKDE Wiki:

 http://www.diotavelli.net/PyQtWiki/Tutorials

Later, when you want to draw graphs, you might find PyQwt useful:

 http://pyqwt.sourceforge.net/

You may already be aware that there's also a mailing list for PyQt and
PyKDE:

 http://www.riverbankcomputing.com/pipermail/pyqt/

Another way to get answers to questions is to join the #pyqt IRC channel
at freenode.net:

  irc://irc.freenode.net/

David

Thanks for the response. I have gone through a lot of the tutorials.
All of them(that I saw) seem to just deal will event-based
applications ie calculator, image viewer, etc. How do I run pyserial
in the background and pass the information to PyQT and refresh the
screen? Is there a way to have pyserial run in another thread and
pass the information to the UI?

Thanks,
Seth

 

[Dennis Lee Bieber]

Thanks for the response. I have gone through a lot of the tutorials.
All of them(that I saw) seem to just deal will event-based
applications ie calculator, image viewer, etc. How do I run pyserial
in the background and pass the information to PyQT and refresh the
screen? Is there a way to have pyserial run in another thread and
pass the information to the UI?

So far as I've experienced (which isn't all that much), most all GUI
frameworks support some method of defining either: 1) a work routine
which will be called whenever the input event queue is empty -- work
routines should be coded to do a very short, fast, bit of processing and
return, so the event dispatcher can continue (collect one character at a
time, or one line using a non-blocking I/O operation; or use a thread to
collect and post via a Queue) (wx.EVT_IDLE [bind to your idle handler] &
wx.WakeUpIdle() [call from thread after posting to queue]); 2) a
timed-event which the dispatcher can call at periodic intervals (use a
thread to collect lines from the serial port, post the lines via a
Queue, and have the timed event check for queued data) (wx.Timer() ); 3)
a callback interface to the GUI event dispatcher which can be invoked
from a separate thread (wx.CallAfter() )

You'll have to track down the equivalent QT functions (I have to
confess, I found the above from "wxPython in Action"; my last real GUI
coding that needed such was nearly 20 years ago, using xt and DECWindows
for the interface, and GKS on X for the data drawing, emulating an
archaic Ramtek graphics engine command set. The idle/work routine
collected commands sent via VMS mailbox to the "display" and generated
GKS operations for them).
--
Wulfraed Dennis Lee Bieber KD6MOG
(e-mail address removed) (e-mail address removed)
HTTP://wlfraed.home.netcom.com/
(Bestiaria Support Staff: (e-mail address removed))
HTTP://www.bestiaria.com/

 

[David Boddie]

Thanks for the response. I have gone through a lot of the tutorials.
All of them(that I saw) seem to just deal will event-based
applications ie calculator, image viewer, etc. How do I run pyserial
in the background and pass the information to PyQT and refresh the
screen? Is there a way to have pyserial run in another thread and
pass the information to the UI?

So far as I've experienced (which isn't all that much), most all GUI
frameworks support some method of defining either: 1) a work routine
which will be called whenever the input event queue is empty -- work
routines should be coded to do a very short, fast, bit of processing and
return, so the event dispatcher can continue (collect one character at a
time, or one line using a non-blocking I/O operation; or use a thread to
collect and post via a Queue) (wx.EVT_IDLE [bind to your idle handler] &
wx.WakeUpIdle() [call from thread after posting to queue]);

I think I can say that idle processing isn't a common idiom in PyQt
applications. After all, you can't guarantee that your application will be
idle or be able to use up idle time in a way that you can rely on, and
perhaps it isn't a good situation to be in if your framework is using up
CPU time by idling.

2) a timed-event which the dispatcher can call at periodic intervals (use
a thread to collect lines from the serial port, post the lines via a
Queue, and have the timed event check for queued data) (wx.Timer() );

In PyQt, the easiest way to do this is with a timer, connecting its
timeout() signal to a slot (method) to perform some processing. A widget
class might be adapted to do this in the following way:

class MyWindow(QWidget):
def __init__(self):
QWidget.__init__(self)
# ... other initialisation ...

timer = QTimer(self)
timer.timeout.connect(self.processData) # PyQt 4.5 signal notation
timer.start(100) # every 100 milliseconds

def processData(self):
# Do your processing here.

There are various ways to use timers with PyQt, but this is a fairly simple
pattern to use.

3) a callback interface to the GUI event dispatcher which can be invoked
from a separate thread (wx.CallAfter() )

I think at this point I would recommend using a separate thread. The idiom
for using threads with PyQt is quite simple, though it helps to go with the
framework and use QThread instead of Python's thread class.

You'll have to track down the equivalent QT functions (I have to
confess, I found the above from "wxPython in Action"; my last real GUI
coding that needed such was nearly 20 years ago, using xt and DECWindows
for the interface, and GKS on X for the data drawing, emulating an
archaic Ramtek graphics engine command set. The idle/work routine
collected commands sent via VMS mailbox to the "display" and generated
GKS operations for them).

The people demand screenshots! ;-)

David