Discussion on: Dead Simple Python: Generators and Coroutines

[rhymes]

Great article Jason!

Just a couple of details:

An exception can be raised at the current yield with foo.raise(). -> with foo.throw().

In sorted(self.letters.items(), key=lambda kv: kv[1]) the lambda can be replaced with operator.itemgetter(1), it's one of my favorite small things that are in the standard library :D

I was wondering if there was a way to simplify the coroutine code, using a context manager. The __enter__ could call send(None) and the __exit__ could call close().

With a simple generator is easy to do something similar:

>>> from contextlib import contextmanager
>>> @contextmanager
... def generator():
...     try:
...             yield list(range(10))
...     finally:
...             print("cleanup...")
...
>>> with generator() as numbers:
...     print(numbers)
...
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
cleanup...

But the same doesn't work for a coroutine...

As a first I came up with this:

from contextlib import closing

def print_char():
    try:
        while True:
            print(f"char: {yield}")
    finally:
        print("cleanup...")

with closing(print_char()) as printer:
    printer.send(None)
    for c in "hello world":
        printer.send(c)

>>>
char: h
char: e
char: l
char: l
char: o
char:
char: w
char: o
char: r
char: l
char: d
cleanup...

I came up with something like this then:

from contextlib import ContextDecorator

class coroutine(ContextDecorator):
    def __init__(self, function):
        self.coro = function()

    def __enter__(self):
        self.coro.send(None)

    def __exit__(self, exc_type, exc, exc_tb):
        self.coro.close()

    def send(self, *args):
        self.coro.send(*args)



def print_char():
    while True:
        print(f"char: {yield}")

printer = coroutine(print_char)
with printer:
    for c in "hello world":
        printer.send(c)

but I'm not sure it's improving much :D

[Jason C. McDonald]

Ooh! Thanks for catching that typo! That would have been confusing.

As to the lambda or itemgetter(), I'd actually gone back and forth between the two in writing that example. I think using the lambda there is my own personal preference more than anything.

That is certainly a clever combination of a context and a coroutine, by the way. (Naturally, I didn't discuss contexts in this article, as I haven't discussed them yet in the series.)

Thanks for the feedback.