I have one other way of sharing the prime number trial by division thing: as coroutines. I owe David Beazley on this one. The coroutine decorator jumps us to the first yield so that we can send numbers in right away.

primes weeds out composites, passing survivor primes to the printing coroutine (passed in as target).

In my Tractor class, a simple object that plows a Field leaving a trail of Unicode characters (raster pattern), I used yield both to output and input (instances would gradually run low on fuel, but one could refill), but David advises against this pattern.

http://mathforum.org/kb/message.jspa?messageID=9507410 (talks about Tractor Math)

# -*- coding: utf-8 -*-
"""
Created on Thu Oct 13 13:48:52 2016

@author: Kirby Urner

David Beazley:
https://youtu.be/Z_OAlIhXziw?t=23m42s

Trial by division, but this time the primes coroutine acts
more as a filter, passing qualified candidates through to
print_me, which writes to a file.
"""

def coroutine(func):
    """
    Advances decorated generator function to the first yield
    """
    def start(*args, **kwargs):
        cr = func(*args, **kwargs)
        cr.send(None)  # or next(cr) or cr.__next__()
        return cr
    return start
       
@coroutine
def print_me(file_name):
    with open(file_name, 'w') as file_obj:
        while True:
            to_print = (yield)
            file_obj.write(str(to_print)+"\n")
   
@coroutine
def primes(target):
    _primes_so_far = [2]
    while True:
        candidate = (yield)
        for prev in _primes_so_far:
            if not divmod(candidate, prev)[1]:
                break
            if prev**2 > candidate:
                _primes_so_far.append(candidate)
                target.send(candidate)
                break

output = print_me("primes.txt")
p = primes(output)

   
for x in range(3, 200, 2):  # test odds 3-199
    p.send(x)

with open("primes.txt", 'r') as file_obj:
    print(file_obj.read())