tkinter catch value from lambda function - python-3.x

Question

I'm trying to wrap my head around this problem.
Say I have a code like this:
def get_input(data_A, data_B):
all_data = [data_A.get(),dataB.get()]
return(all_data)
def the_gui():
root = Tk()
data_A = Entry(root)
data_B = Entry(root)
button = Button(root, text='Submit', command=lambda: get_input(data_A, data_B))
mainloop()
My goal is to get the value of data_A and data_B once I clicked the submit button.
I tried to use global variable and everything, but I kept failing to catch the value.
The only thing that works is when I put the whole get_input() function inside the_gui() function. However, I don't think that's a good practice to implement.
Any suggestions?

Answer 1

Here is a simple example of how you could write this to get the results you are looking for.
When using global is that all your root window and related fields are in a function. So you would have to define global in both function and this is not what you want to do.
Typically you will want to write the root window in the global namespace and not in a function or write it into a class so you can avoid global's all-together.
button = Button(...) may not be doing what you think it is. This does not return a value from the command once clicked. Tkinter buttons do not care about anything being returned. So you have to record that value elsewhere.
I am not sure how you code is working as you do not use geometry managers and mainloop() should be attached to the root window so I have added those in as well.
Example 1:
import tkinter as tk
def get_input():
global a_and_b
a_and_b = [data_a.get(), data_b.get()]
# If you want to keep a running record of all values submitted
# then you can do this instead:
# a_and_b.append([data_a.get(), data_b.get()])
def print_a_b():
print(a_and_b)
root = tk.Tk()
a_and_b = []
data_a = tk.Entry(root)
data_b = tk.Entry(root)
data_a.pack()
data_b.pack()
tk.Button(root, text='Submit', command=get_input).pack()
tk.Button(root, text='Print A/B List', command=print_a_b).pack()
root.mainloop()
Example 2 using OOP:
import tkinter as tk
class App(tk.Tk):
def __init__(self):
super().__init__()
self.a_and_b = []
self.data_a = tk.Entry(self)
self.data_b = tk.Entry(self)
self.data_a.pack()
self.data_b.pack()
tk.Button(self, text='Submit', command=self.get_input).pack()
tk.Button(self, text='Print A/B List', command=self.print_a_b).pack()
def get_input(self):
self.a_and_b = [self.data_a.get(), self.data_b.get()]
def print_a_b(self):
print(self.a_and_b)
if __name__ == '__main__':
App().mainloop()