# Re: [Python-ideas] Add the imath module

```12.07.18 15:15, David Mertz пише:
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On Thu, Jul 12, 2018, 7:56 AM Serhiy Storchaka <storch...@gmail.com <mailto:storch...@gmail.com>> wrote:
```
* isprime(n)
Tests if n is a prime number.

```
How would you test this? The Miller-Rabin Primality test? For large numbers, iterating through candidate prime divisors is pricey.
```
* primes()
Returns an iterator of prime numbers: 2, 3, 5, 7, 11, 13,...

```
How would you implements this? Sieve of Eratosthenes is really fun to show students as a Python generator function. But the cached primes DO grow unboundedly as you utilize the generator. Wheel factorization as first pass? Do you cached the first N primes so the each instance of iterator can provide initial elements much faster? What is N?
```
```
I didn't mean any concrete implementation. Sure there are enough efficient and simple. I sometimes need a sequence of prime numbers for solving toy problems, and quickly write something like:
```
def primes(n):
```
return (i for i in range(2, n) if all(i % j for j in primes(int(sqrt(i)) + 1)))
```
```
Having such feature in the stdlib would be very convenient. Any reasonable implementation is enough efficient for my purposes.
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