prime.py

#!/usr/bin/env python3
# First time I use [[click]] ~ anagora.org/click, it looks cool like the other [[pallets project]], [[flask]], which we use in [[agora server]].
# https://click.palletsprojects.com/en/8.1.x/arguments/
# https://click.palletsprojects.com/en/8.1.x/options/

import click
import math
import sys

# I'm not proud (I am a little bit?).
PROOF = [] # :)

def factor(n):
    for i in range(2, n+1):
        click.echo(f"Is {i} a factor of {n}, I wonder?")

def print_sieve(sieve):
    primes = []
    for n, prime in enumerate(sieve):
        if n >= 2 and prime:
            primes.append(str(n))
    return ", ".join(primes)

def is_prime(n):
    sieve = [True for n in range(0, n+1)]
    upto = math.ceil(math.sqrt(n))
    for i, _ in enumerate(sieve):
        # click.echo(f"i: {i}")
        if i < 2:
            continue
        # If we're above the square root, we can stop considering the first factor, as we'll try higher numbers in the inner loop.
        if i > upto:
            break
        # If this is a known composite, then we've already crossed off its multiples when we iterated over its primes.
        if not sieve[i]:
            continue
        # for j in range(2, math.ceil(math.sqrt(n) + 1)):
        for j in range(2, n):
            # I wrote >= here initially. That did *not* work ;)
            if i * j > n:
                break
            PROOF.append(f"[[{i*j}]] is composite: {i} * {j}.")
            try:
                sieve[i*j] = False
            except IndexError:
                continue
    return (n >= 2 and sieve[n], sieve)

class AgoraCmd(click.Command):
    def format_help(self, ctx, formatter):
        click.echo("""Usage:
        - Visit anagora.org/primes to execute this file in the Agora of Flancia.
        - Visit e.g. anagora.org/primes/17 to test if 17 is prime.
        - In general visit anagora.org/foo, anagora.org/foo/bar to execute e.g. <bin/foo.py bar> from your garden.
        """)

    def __call__(self, *args, **kwargs):
        try:
            return super(AgoraCmd, self).__call__(
                *args, standalone_mode=False, **kwargs)
        except click.MissingParameter as exc:
            exc.ctx = None
            exc.show(file=sys.stdout)
            click.echo()
            try:
                super(AgoraCmd, self).__call__(['--help'])
            except SystemExit:
                sys.exit(exc.exit_code)

@click.command(cls=AgoraCmd)
@click.argument('n', type=click.INT)
def prime(n):
    """Simple program that factors a number using a [[Sieve of Eratosthenes]]."""
    p, sieve = is_prime(n)
    if p:
        click.echo(f"[[{n}]] is *prime*.")
    else:
        click.echo(f"[[{n}]] is *not prime*. Want proof? :)")
        click.echo("\n".join([line for line in PROOF if f'[[{n}]]' in line]))

    click.echo(f"\nPrimes up to {n}: {print_sieve(sieve)}.")

if __name__ == '__main__':
    prime()