Python - creating random number string without duplicates

I need help with creating a random string of 4 numbers without having duplicates.

Code:

from random import randint

correct = [randint(1,8), randint(1,8), randint(1,8), randint(1,8)]
usr_guess = [0, 0, 0, 0]
usr_guess_output = []
usr_guess_output_n = []
print(correct)

Also, if you could help me get the user input without needing commas that would be great!

Full code:

from random import randint

correct = [randint(1,8), randint(1,8), randint(1,8), randint(1,8)]
usr_guess = [0, 0, 0, 0]
usr_guess_output = []
usr_guess_output_n = []
print(correct)

guesses = 0

print('Welcome to Mastermind. Guess the combination of numbers between 1 and 8. If you get the correct number and place, a \'*\' will be printed. If you get the correct number but wrong place, a \'-\' will be printed. If you get it wrong completely, a \'#\' will be printed. The position of the output does not correlate to the positions in the actual list of numbers.')

while(True):
  usr_guess_output_n = []
  usr_guess_output = []
  correct_count = 0
  guesses += 1

#  try: #Makes sure that the program still works even if the user messes up the input

  usr_guess = input('Guess at the numbers (separate with commas) > ').split(',') #Splits the user input into a list of integers

  usr_guess = [int(x) for x in usr_guess ] #Converts all list items into integers for comparisons

  print('')
  i = 0
  for i in range(0,4): #Iterates the lists to check for comparisons

    if correct[i] == usr_guess[i]:
      usr_guess_output.append('*')
      correct_count += 1

    elif correct[i] in usr_guess:
      usr_guess_output.append('-')

    else:
      usr_guess_output.append('#')

  if(correct_count > 3):
    break

  for i in usr_guess_output:
    if i == '*':
      usr_guess_output_n.append('*')
  for i in usr_guess_output:
    if i == '-':
      usr_guess_output_n.append('-')
  for i in usr_guess_output:
    if i == '#':
      usr_guess_output_n.append('#')


  print(str(usr_guess_output_n).replace(',','').replace('[','').replace(']','').replace('\'',''))

#  except:
#    print('something went wrong. you probably input something other than an integer')
#    guesses -= 1

print('\nIt took you ' + str(guesses) + ' guesses!')
input('Press enter to exit')