pythoncard-users

[Pythoncard-users] loop in body of main program

[James W. <ji...@cs...>]

I'm in Windows XP, and I'm trying to write something like this:


while going:
     do stuff


def on_startButton_mouseClick(...):
    going = 1

def on_stopButton_mouseClick(...):
     going = 0


My problem is where to put the loop. The best example I could find in 
the samples was the Gravity program. That program puts the loop in 
the startButton handler, and Gravity works fine on my machine.]When I 
do that in my program, it works  fine until I push the stop button. 
Then it freezes up and I have to kill it. I also tried putting the 
loop in an on_idle(...) method and got the same results.

I got around it finally using a timer and it's handler to replace the 
loop completely, but that's no good to me for two reasons:

2. it's too complicated for beginning students
1. the whole point was to expose them to loops

I think the RIGHT way to do this is to use a thread for the loop, but 
that's also too much for beginning students.


Any advice gratefully accepted.
-- 
-------------------------------------------------------------
Jimmy Wilkinson            | Professor Emeritus of Computer Science
ji...@cs...        | The College of Charleston
(843) 953-8160             | Charleston      SC        29424
http://www.cs.cofc.edu/~jimmy

If there is one word to describe me, that word would have to be 
"profectionist".

Re: [Pythoncard-users] loop in body of main program

[Alex T. <al...@tw...>]

James Wilkinson wrote:
> I'm in Windows XP, and I'm trying to write something like this:
>
>
> while going:
>      do stuff
>
>
> def on_startButton_mouseClick(...):
>     going = 1
>
> def on_stopButton_mouseClick(...):
>      going = 0
>
>
>   
That should (might) work, provided you include some important code 
within the loop (i.e. within "do stuff") - see below.
> My problem is where to put the loop. The best example I could find in 
> the samples was the Gravity program. That program puts the loop in 
> the startButton handler, and Gravity works fine on my machine.]When I 
> do that in my program, it works  fine until I push the stop button. 
> Then it freezes up and I have to kill it. I also tried putting the 
> loop in an on_idle(...) method and got the same results.
>
>   
If you have enough info to 'do stuff' right away, you could simply put 
the loop at the end of your on_initialize() but it's likely that you 
need to let the user set things up before you are ready to 'do stuff', 
so you might need a button (e.g. 'Go') and put the loop within its handler.

The important thing is that you will be in a tight loop (i.e. everything 
will freeze) unless you allow a way for the  user interaction to happen. 
The easiest way to do that (see for example the Gravity sample) is to 
include something like

            # give the user a chance to click Stop
            wx.SafeYield(self, True)

within the loop.
> I got around it finally using a timer and it's handler to replace the 
> loop completely, but that's no good to me for two reasons:
>
>   
More complicated than it needs to be :-)
> I think the RIGHT way to do this is to use a thread for the loop, but 
> that's also too much for beginning students.
>
>   
Much too complicated - not just for beginners, but because it's too 
complicated :-) You only need threads if there is "real work" that could 
be time consuming needing to happen both in the background and the 
foreground parts. For simply setting a variable to stop a loop, there is 
no work, and no need for lengthy processing, in the UI event, so threads 
are very much overkill.


Something along the lines I suggested above, and the Gravity example,  
should work. If you are having trouble, and if it's not too long or 
complicated (or secret) include the whole of your code in the next email 
and we can be more specific. (or simplify 'do stuff' to be something 
simple like 'print going' and then send the whole code ....)


-- 

Alex Tweedly      mailto:al...@tw...      www.tweedly.net

Re: [Pythoncard-users] loop in body of main program

[Phil E. <ph...@li...>]

Okay, probably not the nicest bit of code I've ever written, but it 
seems to do the trick:

-----begin loop-demo.rsrc.py-----
{'application':{'type':'Application',
           'name':'Template',
     'backgrounds': [
     {'type':'Background',
           'name':'bgTemplate',
           'title':u'Loop Demo',
           'size':(380, 220),
           'statusBar':1,
           'style':['resizeable'],

         'menubar': {'type':'MenuBar',
          'menus': [
              {'type':'Menu',
              'name':'menuFile',
              'label':'&File',
              'items': [
                   {'type':'MenuItem',
                    'name':'menuFileExit',
                    'label':'E&xit',
                    'command':'exit',
                   },
               ]
              },
          ]
      },
          'components': [

{'type':'StaticText',
     'name':'StaticText3',
     'position':(10, 45),
     'text':u'environment:',
     },

{'type':'StaticText',
     'name':'StaticText2',
     'position':(10, 30),
     'text':u'known as iteration) in an event-driven programming',
     },

{'type':'Button',
     'name':'stopLoopBtn',
     'position':(115, 125),
     'label':u'Stop Looping',
     },

{'type':'Button',
     'name':'startLoopBtn',
     'position':(10, 125),
     'label':u'Start Looping',
     },

{'type':'Gauge',
     'name':'Gauge1',
     'position':(15, 80),
     'size':(345, 28),
     'backgroundColor':(220, 230, 232, 255),
     'layout':'horizontal',
     'max':10,
     'value':0,
     },

{'type':'StaticText',
     'name':'StaticText1',
     'position':(10, 15),
     'text':u'This program demonstrates a way to control loops (also',
     },

] # end components
} # end background
] # end backgrounds
} }
------end loop-demo.rsrc.py------

-----begin loop-demo.py-----
#!/usr/bin/python
# simple demonstration of looping

# standard Python imports
import time

# PythonCard imports
import wx
from PythonCard import model

class loopDemo(model.Background):

     def on_initialize(self, event):
         self.loopRunning = False
         self.components.stopLoopBtn.enabled = False
         print self.components.Gauge1.max
         print self.components.Gauge1.value

     def on_startLoopBtn_mouseClick(self, event):
         if not self.loopRunning:
             self.components.startLoopBtn.enabled = False
             self.components.stopLoopBtn.enabled = True
             self.components.Gauge1.value = 0
             self.loopRunning = True
             self.countValue = 0
             while self.countValue < self.components.Gauge1.max:
                 self.countValue += 1
                 self.components.Gauge1.value = self.countValue
                 wx.Yield()
                 time.sleep(1)
                 print self.countValue

     def on_stopLoopBtn_mouseClick(self, event):
         if self.loopRunning:
             self.loopRunning = False
             self.countValue = self.components.Gauge1.max + 1
             self.components.startLoopBtn.enabled = True
             self.components.stopLoopBtn.enabled = False
             self.components.Gauge1.value = 0

if __name__ == '__main__':
     app = model.Application(loopDemo)
     app.MainLoop()
------end loop-demo.py------

-- 

Regards

Phil Edwards   |  PGP/GnuPG Key Id
Brighton, UK   |  0x68393AEE

Re: [Pythoncard-users] loop in body of main program

[Phil E. <ph...@li...>]

Phil Edwards wrote:
> Okay, probably not the nicest bit of code I've ever written, but it 
> seems to do the trick:
> 

Extra brownie points for the first person to spot the bug in the code... :-)


-- 

Regards

Phil Edwards   |  PGP/GnuPG Key Id
Brighton, UK   |  0x68393AEE

Re: [Pythoncard-users] loop in body of main program

[XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX]

On 26/03/2008 17:31, Phil Edwards wrote:
> Phil Edwards wrote:
>> Okay, probably not the nicest bit of code I've ever written, but it 
>> seems to do the trick:
>>
> 
> Extra brownie points for the first person to spot the bug in the code... :-)
> 
> 

Well, my brain's fried after a day of wxPython frames, panels, grids and 
  missing scrollbars. So I had to 'cheat' and run your code because I 
couldn't see anything.

Works OK, apart from the mysterious:

self.countValue = self.components.Gauge1.max + 1

which produces a Spinal Tap moment when you hit the stop button...was 
that intentional ;-)

-- 
XXXXXXXXXXX

Re: [Pythoncard-users] loop in body of main program

[Phil E. <ph...@li...>]

Neil Hughes wrote:
> 
> Works OK, apart from the mysterious:
> 
> self.countValue = self.components.Gauge1.max + 1
> 
> which produces a Spinal Tap moment when you hit the stop button...was 
> that intentional ;-)
> 

Sort of - that was my quick and dirty way of ensuring that the loop 
stopped when I wanted it to.

The actual bug I meant was that if you run it and let the loop run to 
completion, it doesn't re-enable the 'Start Loop' button when it's done.

Told you it was rubbish code... :-)


-- 

Regards

Phil Edwards   |  PGP/GnuPG Key Id
Brighton, UK   |  0x68393AEE