Automatic calculation - Remove initial values

Question

I have created a GUI where you can enter values (x values) manually. If you enter a value x1, trace-method will automatically calculate

f(x1)=x1^2=y1 and mean(y) = (1/5 sum_{i=1}^{5} y_i)

So every time an x-value is entered, the corresponding y-value and mean(y) is calculated. The code below works. If you start it you get:

I would like to remove the initial values 0.0 from some cells. The window should look like this when the code is executed:

To get the desired result, I added at the very end before mainloop()

for i in range(1,5):
    y_values[i].set("")
    cells[(i,0)].delete(0,END)

where i remove the initial values of certain cells. If you start the code with this change, the program will not work properly anymore. If you enter an x-value, only the corresponding y-value is calculated, but not mean(y).

Do any of you know why the code with y_values[i].set(""), cells[(i,0)].delete(0,END) no longer works correctly and how to solve this problem?

Here is the full Code (from picture 1):

from tkinter import *
import tkinter as tk

root = Tk()
Label(root, text = "x-values",padx = 10).grid(row = 0, column = 0)
Label(root, text = "y-values",padx = 10).grid(row = 0, column = 1)
Label(root, text = "Mean y", padx = 10).grid(row = 0, column = 2)
# Create Variables 
x_values, y_values = ["x%d" % x for x in range(5)], ["y%d" % x for x in range(5)]
for i in range (5):                     
    x_values[i], y_values[i] = DoubleVar(), DoubleVar()
mean = DoubleVar()

# Create Table 
rows, columns, cells = 5, 2, {}
for i in range(columns):
    for j in range(rows):
        if i == 0: # x-values that can be entered
            b = Entry(root, textvariable=x_values[j])
            b.grid(row = j+1, column = i, sticky = W + E)
            cells[(j,i)] = b
        else: # y-values that are computed by f
            b = Label(root, textvariable=y_values[j])
            b.grid(row = j+1, column = i, sticky = W + E)
            cells[(j,i)] = b

label_mean = Label(root, textvariable = mean).grid(row = 1, column = 2, rowspan = 5)
# compute y-values 
def f(name, index, mode):
    try:
        for i in range(5):
            y_values[i].set(x_values[i].get()**2)
    except tk.TclError:
        pass

# compute mean and standard deviation
def statistic(name, index, mode):
    try:
        y_sum = 0
        for i in range(5):
            y_sum += y_values[i].get()
        y_normalized = y_sum / 5
        mean.set(y_normalized)
    except tk.TclError:
            pass

# Traces to trigger the above functions
for i in range(5):
    x_values[i].trace('w', f)
    y_values[i].trace('w', statistic)

mainloop()

Answer 1

Mean is not calculating because it is raising exception when you tried to add None value to y_sum. Add try block in your statistics function.

def statistic(name, index, mode):
    try:
        y_sum = 0
        for i in range(5):
            try:
                y_sum += y_values[i].get()
            except:
                pass
        y_normalized = y_sum / 5
        mean.set(y_normalized)
    except tk.TclError:
            pass