# Generate 'n' unique random numbers within a range [duplicate] – Dev

The best answers to the question “Generate 'n' unique random numbers within a range [duplicate]” in the category Dev.

QUESTION:

I know how to generate a random number within a range in Python.

``````random.randint(numLow, numHigh)
``````

And I know I can put this in a loop to generate n amount of these numbers

``````for x in range (0, n):
listOfNumbers.append(random.randint(numLow, numHigh))
``````

However, I need to make sure each number in that list is unique. Other than a load of conditional statements, is there a straightforward way of generating n number of unique random numbers?

The important thing is that each number in the list is different to the others..

So

[12, 5, 6, 1] = good

But

[12, 5, 5, 1] = bad, because the number 5 occurs twice.

Generate the range of data first and then shuffle it like this

``````import random
data = range(numLow, numHigh)
random.shuffle(data)
print data
``````

By doing this way, you will get all the numbers in the particular range but in a random order.

But you can use `random.sample` to get the number of elements you need, from a range of numbers like this

``````print random.sample(range(numLow, numHigh), 3)
``````

If you just need sampling without replacement:

``````>>> import random
>>> random.sample(range(1, 100), 3)
[77, 52, 45]
``````

random.sample takes a population and a sample size `k` and returns `k` random members of the population.

If you have to control for the case where `k` is larger than `len(population)`, you need to be prepared to catch a `ValueError`:

``````>>> try:
...   random.sample(range(1, 2), 3)
... except ValueError:
...   print('Sample size exceeded population size.')
...
Sample size exceeded population size
``````

You could use the `random.sample` function from the standard library to select k elements from a population:

``````import random
random.sample(range(low, high), n)
``````

In case of a rather large range of possible numbers, you could use `itertools.islice` with an infinite random generator:

``````import itertools
import random

def random_gen(low, high):
while True:
yield random.randrange(low, high)

gen = random_gen(1, 100)
items = list(itertools.islice(gen, 10))  # Take first 10 random elements
``````

After the question update it is now clear that you need n distinct (unique) numbers.

``````import itertools
import random

def random_gen(low, high):
while True:
yield random.randrange(low, high)

gen = random_gen(1, 100)

items = set()

# Try to add elem to set until set length is less than 10
for x in itertools.takewhile(lambda x: len(items) < 10, gen):
You could add to a `set` until you reach `n`:
``````setOfNumbers = set()
Be careful of having a smaller range than will fit in `n`. It will loop forever, unable to find new numbers to insert up to `n`