Issue clearing the Tkinter Canvas widget using also matplotlib

Question

This plots scattering angle versus detector distance once certain variables have been entered into Entry fields and the 'plot' button has been clicked. This plot shows up in the canvas I have created. The plot method is 'def flup()', about half way down the code which is carried out by clicking the button named 'bgra'.

When I alter the variables in the entry fields then hit plot again the program adds another plot to the canvas, which is fine. What I want to do is add a button who's command is to clear the entire canvas.

Just below the plot method 'flup()' there is the start of a method named def clear() in which I want to define a function which will be used by a button to clear the canvas. That button, you'll notice, has been created a few lines below that and is called 'delete'. Could someone please give me an example of the small piece of code I will need to include in the def clear() method in order that that button will clear the canvas.

from numpy import *
import matplotlib.pyplot as plt
fromTkinter import *
import tkMessageBox
from pylab import savefig
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg,NavigationToolbar2TkAgg
import matplotlib.backend_bases       
from matplotlib.figure import Figure

def rutherford():
    tkMessageBox.showinfo("hello world", j)
def N():
    tkMessageBox.showinfo("Variable N", "Number of alpha particles incident on foil")

def T():
    tkMessageBox.showinfo('Variable t', 'Thickness of foil in metres')

def K():
    tkMessageBox.showinfo('Variable E', 'Kinetic energy of alpha particles in joules')

def atom():
    tkMessageBox.showinfo('Variable Z', 'Atomic number of element from which the foil is made, or the name of the element')



class App:
    def __init__(self, master):
        frame = Frame(master) #creates the first frame

        Button(frame, text = "?", command=N).grid(row=1,column=2) #various help buttons
        Button(frame, text = "?", command=T).grid(row=2,column=2)
        Button(frame, text = "?", command=K).grid(row=3,column=2)
        Button(frame, text = "?", command=atom).grid(row=4,column=2)

        Nlabel = Label(frame, text = "N =").grid(row=1, column=0, sticky=E) #labels next to the entry frame
        tlabel = Label(frame, text="t =").grid(row=2,column=0, sticky=E)    
        Elabel = Label(frame, text="E =").grid(row=3,column=0, sticky=E)        
        Zlabel = Label(frame, text="Z =").grid(row=4, column=0, sticky=E)

        eN=Entry(frame)
        eN.grid(row=1,column=1)
        et=Entry(frame)
        et.grid(row=2,column=1)
        eE=Entry(frame)
        eE.grid(row=3,column=1)
        eZ=Entry(frame)
        eZ.grid(row=4,column=1)

        def flup():         #the plot
            N=float(eN.get())#turn string into float
            t=float(et.get())
            E=float(eE.get())
            Z=float(eZ.get())
            r=10*(10**-10)
            e=1.602*(10**-19)
            a=5*(10**30)
            i = linspace(math.pi/80, math.pi, 1000)
            list =[]

            for p in i:
                b = (N*a*t)/(16.0*(r**2))
                c = ((2.0*Z*(e**2))/(E*4.0*math.pi*8.854*(10**-12)))**2
                d = (1.0/(math.sin(p/2.0)))**4
                n=b*c*d
                list.append(n)

            f=Figure(figsize=(5,4), dpi=100)
            g=f.add_subplot(1,1,1)


            g.plot(i,list)

            canvas=FigureCanvasTkAgg(f, master=master)
            canvas.show()
            canvas.get_tk_widget().pack(side=LEFT, fill=BOTH, expand=1)

            canvas._tkcanvas.pack(side=TOP, fill=BOTH, expand=1)


        #def clear():


        bgra=Button(frame, text = "Plot", command=flup) #this button makes the plot
        bgra.grid(row=5,column=1)

        delete=Button(frame,text='Clear All', command=clear)
        delete.grid(row=5,column=2)




        frame2=Frame(master)

        b1=Button(frame2, text="Rutherford Scattering??", command=rutherford)
        b1.pack(side=LEFT)
        frame2.pack()
        frame.pack()



root = Tk()
app = App(root)
root.mainloop()

Solution

To delete everything on a canvas, call the delete method with an argument of "all". I don't know anything about matplotlib, but I'm guessing you would do something like this:

canvas.get_tk_widget().delete("all")

Comments

[nbro]

Related: stackoverflow.com/questions/15839491/…

[user1821664]

Thanks, I tried this and bizarrely, every time I click the 'clear all' button, which calls the function def clear(), containing this piece of code, the GUI opens a new, empty canvas next to the original which still contains the first plot. I wonder if that is something to do with the line that reads g=f.add_subplot(1,1,1). Perhaps the program is opening a new subplot canvas, the content of which has been deleted but leaves the old one. Either way, any ideas? Thanks again.