Pass tkinter variable to another function

Question

I seem to have great difficulties understanding how functions pass information to one another. Been teaching myself Python for a while now and I always hit a brick wall.

In the example below the create_list() function knows nothing about playerlist or the tkinter widget playerOption. I really don't know how to overcome this problem!

All help very much appreciated. It's been about 6 hours of work today and I've got nowhere! Thanks in advance.

from tkinter import *


def create_list(surname):

    table = r'c:\directory\players.dbf'

    with table:
        # Create an index of column/s
        index = table.create_index(lambda rec: (rec.name))

        # Creates a list of matching values
        matches = index.search(match=(surname,), partial=True)

        # Populate playerOption Menu with playerlist.
        playerlist = []
        for item in matches:
            playerlist.append([item[4], item[2], item[1]])

        m = playerOption.children['menu']
        m.delete(0, END)
        for line in playerlist:
            m.add_command(label=line,command=lambda v=var,l=line:v.set(l))


def main():

    master = Tk()
    master.geometry('{}x{}'.format(400, 125))
    master.title('Assign a Player to a Team')

    entry = Entry(master, width = 50)
    entry.grid(row = 0, column = 0, columnspan = 5)

    def get_surname():

        surname = entry.get()

        create_list(surname)

    surname_button = Button(master, text='Go', command=get_surname)
    surname_button.grid(row = 0, column = 7, sticky = W)

    # Menu for player choosing.
    var = StringVar(master)

    playerlist = ['']
    playerOption = OptionMenu(master, var, *playerlist)
    playerOption.grid(row = 1, column = 1, columnspan = 4, sticky = EW)

    mainloop()


main()

Answer 1

playlist is local variable created in main. You have to create global variable to use it in another function.

# create global variable 

playlist = ['']
#playlist = None


def create_list(surname):
    # inform function `create_list` to use global variable `playlist`
    global playlist

    # assign empty list to global variable - not to create local variable
    # because there is `global playlist`
    playerlist = []

    for item in matches:
        # append element to global variable 
        # (it doesn't need `global playlist`)
        playerlist.append([item[4], item[2], item[1]])



def main():
    # inform function `main` to use global variable `playlist`
    global playlist


    # assign list [''] to global variable - not to create local variable
    # because there is `global playlist`
    playlist = ['']

    # use global variable 
    # (it doesn't need `global playlist`)
    playerOption = OptionMenu(master, var, *playerlist)

You can skip global playlist in function if you don't want assign new list to playlist in that function.