Using tkinter -- How to clear FigureCanvasTkAgg object if exists or similar?

Question

Trying to create a tkinter based window that allows user to create a chart on button click, refreshing the chart -- not adding another, each time. All without creating a new window. The idea is click -> create chart, click again -> replace the chart with new chart in same spot. No extra clicks, no extra button to close. Using matplotlib.backends.backend_tkagg and FigureCanvasTkAgg. Documentation appears to be virtually non-existent on this. Tried various attributes in .get_tk_widget() to see if I could test if it exists already, get a list, etc. Also tried clearing canvas.

from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg
from matplotlib.figure import Figure
from tkinter import *

class testme:
    def __init__(self,frame1):
        self.frame1=frame1     
        self.button=Button(self.frame1,text="DRAWME",command=self.plot) 
        self.button1=Button(self.frame1,text="CLEARME",command=self.clearme)
        self.button.pack()       
        self.button1.pack()      

    def plot(self):                   
        f=Figure(figsize=(5,1)) 
        aplt=f.add_subplot(111)       
        aplt.plot([1,2,3,4]) 
        self.wierdobject = FigureCanvasTkAgg(f, master=self.frame1) 
        self.wierdobject.get_tk_widget().pack() 
        self.wierdobject.draw()                

    def clearme(self):       
       self.wierdobject.get_tk_widget().pack_forget()     

root=Tk()
aframe=Frame(root)
testme(aframe)
aframe.pack()  #packs a frame which given testme packs frame 1 in testme
root.mainloop()

Attached example code almost approximates my goal but it requires a "CLEARME" button (which only works right if "DRAWME" was only clicked once. I just want some kind of if statement that checks if there is a FigureCanvasTkAgg object in the frame already and if so remove it instead of a button click.

After a number of attempts I concluded I have a fundamental misunderstanding of more than one thing that's going on here.

Relevant [how-to-update-a-plot-in-matplotlib](https://stackoverflow.com/questions/4098131/how-to-update-a-plot-in-matplotlib) — stovfl, May 15 '19 at 17:07

score 6 · Accepted Answer · answered May 16 '19 at 02:34

6

For your current setup, just add a try clause at the start of your plot function.

def plot(self):   
    try: 
        self.wierdobject.get_tk_widget().pack_forget()
    except AttributeError: 
        pass                
    f=Figure(figsize=(5,1)) 
    aplt=f.add_subplot(111)       
    aplt.plot([1,2,3,4]) 
    self.wierdobject = FigureCanvasTkAgg(f, master=self.frame1) 
    self.wierdobject.get_tk_widget().pack() 
    self.wierdobject.draw()

answered May 16 '19 at 02:34

Henry Yik

22,275
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1

Nice, that works. Added: `import random` at the top, then a `b=random.randint(4,10)` and changed `aplot.plot([1,2,3,4])` to `aplot.plot([1,2,3,b])` to the code along with your edit. Oh, and remove the `def clearme()` parts. Now I can see it in action. Next is to put it in my larger program. And learn more about the try method and error handling (haven't gotten to those in my Python training yet). Thanks! – Blaine Kelley May 16 '19 at 16:07

Using tkinter -- How to clear FigureCanvasTkAgg object if exists or similar?

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