Emptying a list or dictionary for reuse

July 27, 2022

I have a script that looks like this

import tkinter as tk
from random import randint

a=[]
b=[]
c={}
d={}

def program():
    a.append(1)
    c[randint(10, 20)] = randint(0, 10) 
    do_something()
    do_something_else()

    print(a)
    print(b)
    print(c)
    print(d)
    print('done')

    return

def do_something():
    b.append(15)
    return

def do_something_else():
    d[randint(10, 20)] = randint(0, 10)
    return


root = tk.Tk()
tk.Button(root, text="Run", command=program).pack()
root.mainloop()

The problem here is clicking the button runs the function program() again with the previous values in the lists and dictionaries and so they are just appended. I want an empty dicts and lists everytime program()is called.

I created a function to do just that.

def empty():
    global a,b,c,d
    a=[]
    b=[]
    c={}
    d={}
    return

Ive seen much talk about not using global in functions. What would be a neat way to achieve this?

>Solution :

Just make the variables local to program() and pass them around:

import tkinter as tk
from random import randint

def program():
    a=[]
    b=[]
    c={}
    d={}
    a.append(1)
    c[randint(10, 20)] = randint(0, 10) 
    do_something(b)
    do_something_else(d)

    print(a)
    print(b)
    print(c)
    print(d)
    print('done')


def do_something(b):
    b.append(15)


def do_something_else(d):
    d[randint(10, 20)] = randint(0, 10)


root = tk.Tk()
tk.Button(root, text="Run", command=program).pack()
root.mainloop()

Now each call to program() starts with new collections.