Update Label

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December 13th, 2012, 03:25 PM

xsilvergs

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Join Date: Dec 2012

Posts: 7

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Update Label

Hi, New to Python so please be patient.
I've written my first program after reading a few online tutorials but have now run into a problem. Having spent the last 2 evening trying to sort it out I'm now asking for help. Here is my code:

Code:

from Tkinter import*
import serial

root=Tk()

var = StringVar()
var.set("---")

def getdata():  
    rate_str = ''
    ser = serial.Serial('/dev/ttyAMA0', 9600, timeout=0.5)
    
    while 1:
        datain = ser.readline()
        if datain:
            if datain == ',':
                var.set("666")#used for test
                #var.set = datain
                print "past var.set" #it passed this way
            else:
                rate_str += datain

root.after(1000, getdata)
root.title("Polar HRM")
hrmLabel=Label(root,textvariable=var,font=("Helvetica",300),width=("3"),background=("White"),fg=("Red")).pack()

root.mainloop()

The problem:
When the code runs it creates the Label and fills it with "---".
When I send a comma I wish it to take the three numbers held in the "var" and update the Label but it doesn't work it just remains with the 3 dashes.
Can anyone explain and educate me please?

December 13th, 2012, 03:41 PM

rrashkin

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I think the problem is scope. To do it the way you have it now, you need to make "var" global ("global var") in the function.

December 13th, 2012, 04:02 PM

xsilvergs

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Join Date: Dec 2012

Posts: 7

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Quote:

Originally Posted by rrashkin

I think the problem is scope. To do it the way you have it now, you need to make "var" global ("global var") in the function.

Thanks for reply.
If you mean like this:

Code:

def getdata():
     global var
     rate_str = '' 
     ser = serial.Serial('/dev/ttyAMA0', 9600, timeout=0.5)

It still doesn't work. Have you another suggestion?

December 13th, 2012, 04:12 PM

rrashkin

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Location: 39N 104.28W

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Well, yes I do. I use Tk a lot in Tcl but I have found the textvariable option in Python's Tkinter never works quite right for me (I've never tried it in labels but I gave up on it in entries). I prefer to use the <widget>.config(text="blah") method.

December 13th, 2012, 07:32 PM

dwblas

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Sometimes you have to call update_idletasks(). I can never remember the particular circumstances, but try it first when things don't happen as they should. Also, you should sleep during each cycle otherwise this program could hog the computer.

Code:

from Tkinter import*
##import serial
import time

root=Tk()

var = StringVar()
var.set("---")

def getdata():  
    rate_str = ''
##    ser = serial.Serial('/dev/ttyAMA0', 9600, timeout=0.5)
    datain = ","
    Label(root,textvariable=var,font=("Helvetica",300),width=("3"),background=("White"),fg=("Red")).pack()
    ctr = 0
    while ctr < 50:
        ctr += 1
        time.sleep(0.2)
##        datain = ser.readline()
        if datain 
            if datain == ',':
                var.set(str(ctr))#used for test
                #var.set = datain
                root.update_idletasks()
                print "past var.set" #it passed this way
            else:
                rate_str += datain

root.after(1000, getdata)
root.title("Polar HRM")

root.mainloop()

Last edited by dwblas : December 13th, 2012 at 07:40 PM.

December 14th, 2012, 09:16 AM

xsilvergs

Registered User

Join Date: Dec 2012

Posts: 7

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dwblas,

Thanks for help. Here is the code so far which updates the Label.

Code:

from Tkinter import*
import serial
import time

root=Tk()
var = StringVar()

def getdata():  
    rate_str = ''
    ser = serial.Serial('/dev/ttyAMA0', 9600, timeout=0.5)
    Label(root,textvariable=var,font=("Helvetica",300),width=("3"),background=("White"),fg=("Red")).pack()

    while TRUE:
        time.sleep(0.2)
        datain = ser.read()             #read 1 byte
        if datain:                      #is there data in the buffer
            if datain == ',':           #if it's a comma print var to screen
                #print "comma"
                var.set(str(rate_str))  #value to send to Label
                root.update_idletasks()
                rate_str = ''           #clear var
            else:
                rate_str += datain      #concat values
                print rate_str

root.after(1000, getdata)
root.title("Polar HRM")

root.mainloop()

I want to develop it more so will be back for more help in the future.

December 14th, 2012, 10:57 AM

Dietrich

Contributing User

Join Date: Feb 2005

Posts: 483

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Thanks for the nice information xsilvergs

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