How to generate a random 4 digit number not starting with 0 and having unique digits?

Question

This works almost fine but the number starts with 0 sometimes:

import random
numbers = random.sample(range(10), 4)
print(\'\'.join(map(str, numbers)))
         


        

Answer 1

Combine generators with next

A Pythonic way to write would be to use 2 nested generators and next:

from random import randint
from itertools import count

print(next(i for i in (randint(1023, 9876) for _ in count()) if len(set(str(i))) == 4))
# 8756

It's basically a one-liner variant of @MSeifert's answer

Preprocess all the acceptable numbers

If you need many random numbers, you could invest some time and memory for preprocessing all the acceptable numbers:

import random    
possible_numbers = [i for i in range(1023, 9877) if len(set(str(i))) == 4]

1023 and 9877 are used as boundaries because no int lower than 1023 or greater than 9876 can have 4 unique, distince numbers.

Then, you'd just need random.choice for a very fast generation:

print(random.choice(possible_numbers))
# 7234