Unique Number Generator in Python

Question

I am trying to make a number generator for a project I am working on, and I need every number to be unique. The range is '0-100000'. I have the following:


    for i in range (1,100000):
        num = random.randint(0, 100000)
        store = num
        print (num)
        num = random.randint(0, 100000)
        if num == store:
            num = '-'
        print(num)

I can't go through all the outputs in a timely manner, but at a glance, I have seen two issues with them. Firstly, there are repeats, because 'store' gets changed every time, and is only one number. Secondly, one of the outputs, on my current output screen, is '4183053688'. The range doesn't allow for that, so I don't know what happened.

I have only thought of two possible answers. Firstly I have played around with making a list to check whether a number has been used or not, but I haven't found a way to update it as numbers come in, and I will be using so many number in a short time, that manually putting them in is impractical. My second idea is what the code shows. But those problems have already been explained.

What's the problem with 0, 1, 2, 3, 4, etc. Those are unique. Or it must be random too? — simre, Aug 14 '23 at 12:13
@luk2302 I just tried that, and it did not work. No outputs happened. — Brendan Carey, Aug 14 '23 at 12:15
Then I think you should check `set` in python. You can just push random numbers in it until you get the required number of numbers. In a set you cannot have duplicates so it'll insert or do nothing if it's there already. Not the most effective way but really simple — simre, Aug 14 '23 at 12:18
The answers there are perfect duplicates, there is nothing more to do than use one of them. — luk2302, Aug 14 '23 at 12:18
@simre I tried that, but I am incredibly bad at programming, so do you mind explaining it? — Brendan Carey, Aug 16 '23 at 13:27
I mean what I said: the linked question and its answers perfectly answers this question and anything that is posted here will just be a duplicate / repetition of what has already been posted there. — luk2302, Aug 16 '23 at 13:28
@luk2302 It does not work though? I tried what the link led me to, and the program did not output anything. Not even an error. — Brendan Carey, Aug 16 '23 at 13:30

score 2 · Accepted Answer · answered Aug 14 '23 at 12:19

2

random.sample with range specified does the job for your reference

import random
unique_numbers = random.sample(range(0, 100001),100000)
print(unique_numbers)

answered Aug 14 '23 at 12:19

yashaswi k

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If you're sampling the entire range why not just build a list and shuffle it? – DarkKnight Aug 14 '23 at 13:57

score 0 · Answer 2 · answered Aug 14 '23 at 13:52

0

So what you're saying is that you want all the numbers in a range returned in a random order. Therefore:

from random import shuffle

def func(r: range) -> list[int]:
    _list: list[int] = list(r)
    shuffle(_list)
    return _list

print(func(range(100_000)))

Note:

This will return a list comprised of all values in the range. If you don't need the full list then just slice it

answered Aug 14 '23 at 13:52

DarkKnight

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So. I am extremely bad at programming, so could you possibly explain what this does? – Brendan Carey Aug 16 '23 at 13:29
@BrendanCarey It makes a list from a range then pseudo-randomly rearranges that list (shuffle) and returns it – DarkKnight Aug 16 '23 at 13:35
Got it...I think. Thanks for the help. Apologies for taking your time with a beginner question. – Brendan Carey Aug 16 '23 at 13:37

simre · Answer 3 · 2023-08-17T09:42:44.707

You asked me to explain the "set" solution to this problem in comment. So this is a possible solution:

s = set()
while len(s) < 100:
    s.add(random.randint(0, 1000))

A set is an unordered collection without duplicates, so you cannot add the same number multiple times.

The code above add random numbers to the set called s until its length reaches your target length. But you must be sure to request less or equal numbers than the input range of the randint function or you will run into an infinite loop. Also avoid to request roughly the same length of the input range or you will simply get [0, 1, 2, 3, ...] which will be a unique list but not really random...

In performance it is not the best. Up to a few hundred thousand elements it can finish in a fraction of a second. But as you increase the required random numbers your runtime will explode.

Unique Number Generator in Python

3 Answers3