How to generate effectively a random number that only contains unique digits in Python?

import random

def get_number(size):
  result = [random.randint(1,9)]
  digits = list(range(0,10))
  digits.remove(result[0])
  if(size > 1):
    result += random.sample(digits,size-1)
  return ''.join(map(str,result))

print(get_number(4))

I solved the problem, but I feel that it's clumsy. How can I do this more effectively and more elegant?