How can you make it simpler?

[DreamingInsanity]

I'm not sure what the parameter "x" does - could you expand on that?

If you just want a 4 digit number with not repeating digits, you could try this:

def fourdigit():
  n = random.randint(1000, 9999) #randomly picks a 4 digit number
  digits = set(str(n)) #it creates a list of all of the characters in the numer
  if(len(digits) < len(str(n))): #set() ignore duplicates, so if there is a any duplicates the length of the list will be less than the original number
    return fourdigit() #therefore call it recursively until there is a value with no repeating digits
  return n #return the value

When I ran that over and over again I didn't see any values with any duplicate numbers.