Tkinter is the easiest way if you don’t want to have any other dependencies.
To show only the dialog without any other GUI elements, you have to hide the root window using the withdraw
method:
import tkinter as tk
from tkinter import filedialog
root = tk.Tk()
root.withdraw()
file_path = filedialog.askopenfilename()
Python 2 variant:
import Tkinter, tkFileDialog
root = Tkinter.Tk()
root.withdraw()
file_path = tkFileDialog.askopenfilename()