How to use user input that was taken from a simple pyton tkinter gui

I would like to take input from a user, then create a variable that stores this input and use it in the next part of code. For example I would like to take a filename from user, then create a dataframe and then do some dataframe manipulation after the gui has been closed.

import tkinter as tk
from tkinter import filedialog
import pandas as pd

def show_entry_fields():
    print("First Name: %s\nLast Name: %s" % (e1.get(), e2.get()))

def UploadAction(event=None):
    filename = filedialog.askopenfilename()
    print('Selected:', filename)

def UploadAction2(event=None):
    filename2 = filedialog.askopenfilename()
    print('Selected:', filename2)

master = tk.Tk()
master.title('App')
master.geometry('300x120')
master['bg'] = '#ffbf00'
tk.Label(master,
         text="Something").grid(row=0)
tk.Label(master,
         text="Something").grid(row=1)

e1 = tk.Entry(master)
e2 = tk.Entry(master)

e1.grid(row=0, column=1)
e2.grid(row=1, column=1)

tk.Button(master,
          text='Close',
          command=master.quit).grid(row=2,
                                    column=0,
                                    sticky=tk.W,
                                    pady=4)
tk.Button(master,
          text='Save', command=show_entry_fields).grid(row=2,
                                                       column=1,
                                                       sticky=tk.W,
                                                       pady=4)

tk.Button(master, text='Open', command=UploadAction).grid(row=3,column=0,sticky=tk.W,pady=4)
tk.Button(master, text='Open', command=UploadAction2).grid(row=3,column=1,sticky=tk.W,pady=4)
tk.mainloop()