Python Digit Calculator

# Digit calculator. Code by Umut Bilgic.
# 1/8/2014 12:42 AM

import math

def calc(a,n):
    return ((math.ceil(n*math.log(a,10)))+1)
def blank():
    print ("")
def seperate():
    print ("________________________________")

print ('''This program lets you calculate the number of digits
the number "a^n" has.''')

while True:

    blank()
    user_a = int(input("a = "))
    blank()
    user_n = float(input("n = "))
    blank()
    print (calc(user_a, user_n))
    blank()

    user_e = str(input("Would you like to exit (y/n): "))
    blank()
    if user_e == ("y") or user_e == ("Y") or user_e == ("yes") or user_e == ("YES"):
        sys.exit("User exit.")
    elif user_e == ("n") or user_e == ("N") or user_e == ("no") or user_e == ("NO"):
        pass
    else:
        seperate()
        print ("Did not recognized, continuing...")
    seperate()