how to make a variable in python turtle code example

Example: how do you create a variable in python turtle

import turtle

frank = turtle.Turtle()

frank.shape("turtle")

# then to create a variable you write (you can call your var anything): 

def variable_name():
for i in range(4)
  frank.forward(20)
  frank.right(90)
  
 #then to run this you just right


variable_name()