Generating Random Numbers for a Combat Simulator

I am attempting to create a very basic Combat Simulator. Here is my code:

import random
#from random import * I had, at one time, created a D20 generator that used the * function. I have since removed it in favor of using randint()
sword = 0
D20 = 0

class Hero:

    def swing_and_hit(sword, D20):

        sword = D20
        print(D20)
        if sword >= 10:
            print("You have defeated the Villian!")

        elif sword  < 10:
            print("You have died!")

D20 = randint(1,20)
Adventurer = Hero
#Adventurer.D20_Func()  Ignore this...aborted effort to try something
Adventurer.swing_and_hit(sword, D20)

Every time I run this at http://ift.tt/XeHtMf, the random number generator outputs 13. I cannot figure out why it does this...any thoughts? I have tried nesting the random number generation inside the function swing_and_hit, and it still generates the same number every time I run the program.