Given a number n, determine what the nth prime is.
By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.
If your language provides methods in the standard library to deal with prime numbers, pretend they don't exist and implement them yourself.
Sometimes it is necessary to raise an exception. When you do this, you should include a meaningful error message to indicate what the source of the error is. This makes your code more readable and helps significantly with debugging. Not every exercise will require you to raise an exception, but for those that do, the tests will only pass if you include a message.
To raise a message with an exception, just write it as an argument to the exception type. For example, instead of
raise Exception, you should write:
raise Exception("Meaningful message indicating the source of the error")
To run the tests, run the appropriate command below (why they are different):
Alternatively, you can tell Python to run the pytest module (allowing the same command to be used regardless of Python version):
python -m pytest nth_prime_test.py
-v: enable verbose output
-x: stop running tests on first failure
--ff: run failures from previous test before running other test cases
For other options, see
python -m pytest -h
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exercism debug and looking for the line that starts with
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A variation on Problem 7 at Project Euler http://projecteuler.net/problem=7
It's possible to submit an incomplete solution so you can see how others have completed the exercise.
import unittest from nth_prime import nth_prime # Tests adapted from `problem-specifications//canonical-data.json` @ v2.1.0 class NthPrimeTest(unittest.TestCase): def test_first_prime(self): self.assertEqual(nth_prime(1), 2) def test_second_prime(self): self.assertEqual(nth_prime(2), 3) def test_sixth_prime(self): self.assertEqual(nth_prime(6), 13) def test_big_prime(self): self.assertEqual(nth_prime(10001), 104743) def test_there_is_no_zeroth_prime(self): with self.assertRaisesWithMessage(ValueError): nth_prime(0) # additional track specific test def test_first_twenty_primes(self): self.assertEqual([2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71], [nth_prime(n) for n in range(1, 21)]) # Utility functions def setUp(self): try: self.assertRaisesRegex except AttributeError: self.assertRaisesRegex = self.assertRaisesRegexp def assertRaisesWithMessage(self, exception): return self.assertRaisesRegex(exception, r".+") if __name__ == '__main__': unittest.main()
import math class prime: @classmethod def nth_prime(cls, n): primes =  possible = cls.possible_primes() while len(primes) < n: x = next(possible) if cls.is_prime(x): primes.append(x) return primes[n - 1] @staticmethod def is_prime(x): for i in range(2, int(math.sqrt(x)) + 1): if x % i == 0: return False return True @staticmethod def possible_primes(): yield 2 n = 3 while True: yield n n += 2 def nth_prime(n): return prime.nth_prime(n)
A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.
Here are some questions to help you reflect on this solution and learn the most from it.