is_prime.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
Determine whether integer is a prime or not.

- *Module*: is_prime
- *Platform*: Unix, Windows
- *Author*: [mailto:[email protected]?subject=About is_prime.py|Greg Meece]
"""

# these imports only needed for testing purposes...
import os
import time

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def is_prime(n):
    """Returns *True* if _n_ is a prime number; otherwise returns *False*."""
    import math
    if n == 1:
        return False

    if n == 2:
        return True

    if n > 2 and n % 2 == 0:
        return False

    max_divisor = math.floor(math.sqrt(n))
    for d in range(3, 1 + int(max_divisor), 2):
        if n % d == 0:
            return False
    return True

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def main():
    """Embedded routines are run as a crude test."""
    this_filename = os.path.basename(__file__)
    print(f"\nThis module ('{this_filename}') has been called directly.")

    print("\n-------------- Exercising is_prime Function ---------------\n")

    for n in range(1, 21):
        print("Is {:>2} prime? {}!".format(n, is_prime(n)))

    print("\n--------------- Timing 'is_prime' Function ----------------\n")

    top_int = 100000  # How large a set of integers do you want to time for?
    t0 = time.time()
    for n in range(1, top_int):
        is_prime(n)
    t1 = time.time()
    print(f"Seconds required to evaluate {top_int:,d} integers: {t1 - t0}\n")


if __name__ == '__main__':
    main()