Trying to make two different strings from the same root

[De1uge]

import random

a = input()

# This is where I'm stuck
mark1 = ["*", "__", "~~"]
mark2 = ["*", "__", "~~"][:-mark1]
#I don't know the correct intonation to replace "[:-mark1]"
#This gives an error due to it not being an actual command

g = random.randint(1,2)
if g == 1:
  if mark1 == "*":
    mark1 = "*"*random.randint(1,3)
    e = random.choice(mark1) + random.choice(mark2)
    f = e[::-1]
    print(e + a + f)
  else:
    e = random.choice(mark1)
    if mark1 == "*":
      e = "*"*random.randint(1,3)
      print(e + a + e)

All I need to be able to do is to give a string which will randomly surround text "a" with either *, __ or ~~. In addition, I need it to (50% of the time) be able to add these together with the second reversed: eg. __*Hello*__

Any help would be much appreciated, I'm still a new coder trying to practice some strings