[Edu-sig] pep380: yield from

[kirby urner]

I working through Luciano's Fluent Python, which I really appreciate
reading in Safari On-Line as so many of the links are live and relevant.
Luciano packs his 'For Further Reading' with links directly in Google
groups, where we can see Guido studying Twisted so to better communicate
his alternative vision in asyncio (formerly tulip).

Here's a tiny test module I'm using, based on Gregory Ewing's PEP 380.

https://www.python.org/dev/peps/pep-0380/

from itertools import takewhile

def fibo(a,b):
    "Fibonacci Numbers with any seed"
    while True:
        yield a
        a, b = a + b, a


def pep380(EXPR):
    _i = iter(EXPR)
    try:
        _y = next(_i)
    except StopIteration as _e:
        _r = _e.value
    else:
        while 1:
            try:
                _s = yield _y
            except GeneratorExit as _e:
                try:
                    _m = _i.close
                except AttributeError:
                    pass
                else:
                    _m()
                raise _e
            except BaseException as _e:
                _x = sys.exc_info()
                try:
                    _m = _i.throw
                except AttributeError:
                    raise _e
                else:
                    try:
                        _y = _m(*_x)
                    except StopIteration as _e:
                        _r = _e.value
                        break
            else:
                try:
                    if _s is None:
                        _y = next(_i)
                    else:
                        _y = _i.send(_s)
                except StopIteration as _e:
                    _r = _e.value
                    break
    return _r

def get_em():
    # fibs = fibo(0,1)
    # yield from fibs  # delegates to subgenerator
    # return fibs
    return pep380(fibo(0,1))

g = get_em()

print(tuple(takewhile(lambda n: n < 1000, g)))


Console output:
(0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987)

Now if I comment out differently:

def get_em():
    fibs = fibo(0,1)
    yield from fibs  # delegates to subgenerator
    # return fibs
    # return pep380(fibo(0,1))

Same answer:
(0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987)

One may also return fibs directly from get_em, showing that 'yield from' is
driving the same process i.e. delegation is happening.

Just scratching the (itchy) surface.

Kirby
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.python.org/pipermail/edu-sig/attachments/20160104/a248d86e/attachment.html>