Python: how to pass a function as a variable command in Tkinter

Question

This is my first time creating a GUI using Tkinter to simulate a DSP setup. I'm stuck.

This GUI requires multiple scales. Therefore I wrote a generic scale function.

# Overlap percent scale  
def overlap_percent():
    print("Testing")
    # op=var.get()
    # olive_features['overlap_perc']=op

    # generic scale function
def create_scale(self,parent,xval,yval,start,end,resolution,orient,default,lng,clr,cmdtrig):
    OHA_scale = tk.Scale(parent,resolution=resolution, from_=start, to=end, orient=orient,length=lng,fg=clr,command=cmdtrig)
    OHA_scale.grid(row=xval, column=yval, sticky=tk.E + tk.W + tk.N + tk.S, padx=20, pady=4)
    OHA_scale.set(default)


    # Overlap %
    yval=yval+2
    xval=1
    self.create_label(Oliveframe,xval,yval,"Overlap %")
    xval=3
    self.create_scale(Oliveframe,xval,yval,25,75,25,"vertical",75,90,'Black',"overlap_percent")
    xval=1
    yval=yval+1
    self.create_arrow(Oliveframe,xval,yval)

Based on the code above, i figured it would print 'Testing' on the cmd line, when i adjust the Overlap scale. Nothing happened. To test the code, i replaced the command in generic scale to

def create_scale(self,parent,xval,yval,start,end,resolution,orient,default,lng,clr,cmdtrig):
    OHA_scale = tk.Scale(parent,resolution=resolution, from_=start, to=end, orient=orient,length=lng,fg=clr,command=overlap_percent)

This resulted in an error.

OHA_scale = tk.Scale(parent,resolution=resolution, from_=start, to=end, orient=orient,length=lng,fg=clr,command=overlap_percent) NameError: name 'overlap_percent' is not defined

I can't quite figure out what I'm doing wrong. How exactly can i use the generic scale function to control multiple scales?

where you modified the command function generic scale exactly — Sideeg MoHammed
– Sideeg MoHammed, Commented Sep 15, 2020 at 7:24
i modified my OP to highlight how i modified the command function. — whoknowsmerida
– whoknowsmerida, Commented Sep 15, 2020 at 7:44
If overlap_percent() is within the class, then self.overlap_percent should be used instead. — acw1668
– acw1668, Commented Sep 15, 2020 at 7:52
So you define overlap_percent() wrong, should be def overlap_percent(self, value) instead. — acw1668
– acw1668, Commented Sep 15, 2020 at 7:59
You can pass an extra argument, for example name, to create_scale(...): def create_scale(..., cmdtrig, name): and pass the name to the generic function: tk.Scale(..., command=lambda v: cmdtrig(name, v). Then define the generic function like def some_function(self, scale_name, value):. You can then create scales like create_scale(..., self.some_function, 'scale1'), create_scale(..., self.some_function, 'scale2') and etc. — acw1668
– acw1668, Commented Sep 15, 2020 at 8:22

Salim Baskoy · Accepted Answer · 2020-09-15 07:44:51Z

2

on this line

OHA_scale = tk.Scale(parent,resolution=resolution, from_=start, to=end, 
orient=orient,length=lng,fg=clr,command=cmdtrig)

command take function parameters but you send a string value

self.create_scale(Oliveframe,xval,yval,25,75,25,"vertical",75,90,'Black',overlap_percent)

If you do it will be alright

answered Sep 15, 2020 at 7:44

Salim Baskoy

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2 Comments

whoknowsmerida Over a year ago

I did try that before I posted my question. It ends up with an error NameError: name 'overlap_percent' is not defined similar to what I showed in the OP when i modified the scale function. I thought it might be due to the sequential order . so i played around with the order, still no luck :(

whoknowsmerida Over a year ago

yes. i tried self.overlap_percent . That resulted in " TypeError: overlap_percent() takes 0 positional arguments but 2 were given " . i didn't quite understand how 2 arguments were given.

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