Tkinter : trying to return value from a button

Question

I have no idea of how to solve my problem i have a code that looks like this:

def f(x):
    x=x.get()
    y=x**2
    z=x-1

Mylist=[]
x=Entry(master)
cmd=lambda x=x : f(x)
Button(master, text="Ok", command=cmd).pack()

What i want to do is something like

Mylist.append([y,z])

In order to use my results somewhere else in my program

Also i know that i could use a class but teachers don't want us to use class for that project...

Do you have any idea ?

Answer 1

The whole point of attaching a command to a button is to implement the answer to the question "what do I want to happen when I click the button?". In your case, the answer is "I want it to a) get the value from an entry widget, b) calculate a new value, and c) append it to a list".

So, write a function that does that, and then call that function from your button. In this case you don't need lambda since you have a 1:1 relationship between the button and entry widget. There's nothing wrong with lambda per se, but in this case it adds complexity without providing any value so I recommend not using it. By not using lambda, the code will be easier to debug and maintain over time since it's hard to set breakpoints or add additional functionality inside a lambda.

For example:

def f(x):
    y=x**2
    z=x-1

def do_calculation():
    x_value = float(x.get())
    result = f(x_value)
    my_list.append(result)

...
tk.Button(..., command=do_calculation)

Answer 2

Use append(f(x)) in lambda and return [y,z] in f(x). And you have to convert string from Entry into int or float.

import tkinter as tk

# --- functions ---

def f(x):
    x = int(x.get()) # convert string to int (or float)
    y = x**2
    z = x-1
    return [y, z]

# --- main ---

my_list = []

master = tk.Tk()

e = tk.Entry(master)
e.pack()

cmd = lambda x=e:my_list.append(f(x))

tk.Button(master, text="Ok", command=cmd).pack()

master.mainloop()

print(my_list)

You can convert x in lambda and then f(x) could do only math calculations

EDIT: corrected version as @TadhgMcDonald-Jensen noted in the comment.

def f(x):
    return [x**2, x-1]

#cmd = lambda x=int(e.get()):my_list.append(f(x)) # wrong version
cmd = lambda:my_list.append(f(int(e.get()))) # correect version

Answer 3

You know clicking the button will execute cmd, so put whatever you want done (including appending to a list) in there. Note that this would mean either changing cmd to not be a lambda, or adding this functionality to f (or something even more esoteric).