Inter-Process comunication

[Zunbeltz Izaola]

Hi

I'm writting a program to get data from a machine. I'm using wxPython
to build the GUI. I've a mehtod in a class that get the data,
something like this:

data = []
def Measure(self):
do somehting...
while ...
point = getdatapoint()
data.aapend(point)
do something...

I want to plot the data in a "canvas", but i want to replot each time
a point is added to data. I don't watn to insert the code to plotting
inside the Measure (becose this code is GUI dependent). The code for
plotting is in another function DrawPlOt()

I want something like to send a signal each time the data is changed
to execute DrawPlot(). I'm no proffesional programmer and i don't know
wich technique is the best, signals, theread, anothero one ...
Any sugestions?

TIA

Zunbeltz Izaola
--
Remove XXX from email: zu******@wm.lc.ehu.esXXX

[Irmen de Jong]

Zunbeltz Izaola wrote:

I want something like to send a signal each time the data is changed
to execute DrawPlot(). I'm no proffesional programmer and i don't know
wich technique is the best, signals, theread, anothero one ...
Any sugestions?

Have a look at Pyro, http://pyro.sourceforge.net
You could stick your DrawPlot() method in a Pyro object
and call it -remotely- from the process/thread that
generated new data to plot.

--Irmen

[Cameron Laird]

In article <3f***********************@news.xs4all.nl>,
Irmen de Jong <[e-mail]> wrote:

Zunbeltz Izaola wrote:

I want something like to send a signal each time the data is changed
to execute DrawPlot(). I'm no proffesional programmer and i don't know
wich technique is the best, signals, theread, anothero one ...
Any sugestions?

Have a look at Pyro, http://pyro.sourceforge.net
You could stick your DrawPlot() method in a Pyro object
and call it -remotely- from the process/thread that
generated new data to plot.

[email9898989]

Zunbeltz Izaola <zu******@wm.lc.ehu.es.XXX> wrote in message news:<m1************@lcpxdf.wm.lc.ehu.es>...

I want to plot the data in a "canvas", but i want to replot each time
a point is added to data. I don't watn to insert the code to plotting
inside the Measure (becose this code is GUI dependent). The code for
plotting is in another function DrawPlOt()

I want something like to send a signal each time the data is changed
to execute DrawPlot(). I'm no proffesional programmer and i don't know
wich technique is the best, signals, theread, anothero one ...
Any sugestions?

First do you want your data collecting class running as a separate
thread in your wxPython app (simplest way), or as a completely
separate process/application that communicates remotely with your
wxPython app?
To do it using threads, see:
http://wiki.wxpython.org/index.cgi/LongRunningTasks
If it is running as a separate application, then you would need to use
something like sockets/Pyro/Twisted to communicate with your wxPython
app.

Second, if you are just plotting the data, see something like wxPyPlot
or SciPy's wxPython plotting options.
http://scipy.com/
http://www.cyberus.ca/~g_will/wxPython/wxpyplot.html

Next, see the Observer-Observable and Model-View-Controller patterns.
Bruce Eckel has an example of observer and observable in Python:
http://jamesthornton.com/eckel/TIPython/code/util/

Make your data collecting class (the Model) a subclass of Observable.
When it gets new data, it calls its own "notifyObservers" method, and
optionally passes the data value (with or without a time stamp too) as
an argument.

Your wxPython canvas (the View) subclasses Observer, and implements a
"notify" method to receive the new data and draw it. But don't redraw
it immediately if the Model is running in a separate thread, use
something like wxCallAfter(self.RedrawPlot) so that all drawing
happens in the main wxPython application thread (or if you are using
SciPy, see its gui_thread module).

One other problem - if your model is continuously collecting a lot of
data very fast, then your wxPython app will get bogged down if you
redraw every time new data is received. What I do is have the
"notify" method just append the time stamped data to an array (see the
Numeric module). Then I use a wxTimer to draw the new data at regular
intervals.