How to make a program that can be opened with a file? (python)

I was making a program that opens a file and does a few things to it, and I wondered if there was a way that you could click on a file, and it would open it in the program, instead of going into the program, clicking open, and navigation through the files to find it, or just a way where you can click "Open With..." and select your program. Here is the code if it helps:

from tkinter import *
from tkinter import filedialog
from subprocess import *
import os

root = Tk()
root.title("Snake converter")
def open_file():

    filename = filedialog.askopenfilename(filetypes = (("Snake files", "*.sim"),("Python Files", "*.py"),("All files", "*.*")))
    filenametmp = filename + ".tmp"
    print filename + " is being compiled. Please wait..."
    tf = open(filenametmp, "a")
    f = open(filename, "r")
    filecontents = f.read()
    tf.write("from simincmodule import *" + "\n")
    tf.write(filecontents)
    os.chdir("C:\Snake\info\Scripts")
    print os.getcwd()
    call(["pyinstaller", filenametmp])
    os.remove("C:/Snake/info/Scripts/build")
    f.close()
    tf.close()
    print "\n\n----------------------------------------------------------------------\n\nFinished compiling " + filename + ". Find the program under [filename]/[filename].exe"

openbutton = Button(root, text = "Open", width = 10, command = open_file)
openbutton.pack()

root.mainloop()

Any help or suggestion will be highly appreciated.

Thanks!