[Python-ideas] PEP 479: Change StopIteration handling inside generators

[Chris Barker]

I htink I'm getting closer to clarity here, but:

let's say I have this silly  helper function (similar to the one in the
PEP):

## (sorry -- python2)

def helper(x):
    if x > 2:
        raise StopIteration
    else:
        return x

# I call that helper from both an iterator class and a generator function.

class Iter(object):
    def __init__(self): self.x = 0
    def __iter__(self): return self
    def next(self):
        if self.x == 3: raise StopIteration
        self.x += 1
        return helper(self.x)


def gen():
    yield helper(1)
    yield helper(2)
    yield helper(3)

# first just loop through them:

for i in Iter():
    print i

for i in gen():
    print i

# they act exactly the same

# then put them inside generator expression and loop through that:

for j in ( i for i in gen() ):
    print j

for j in ( i for i in Iter() ):
    print j

# they still act exactly the same.

Would this PEP chance that? would that StopIteration bubble up through the
iterator class, but not through the generator function? If so then I'm -1
on the PEP.

The only change made by this proposal is that StopIteration becomes,
> in a generator, like any other unexpected exception.


but from the user's perspective, an iterator and a generator should look
the same.

And I think from the perspective of the author of a given generator
function, they should look as much the same as possible-- i.e. if a
StopIteration is raised internally, it will behave the same way as it would
in a iterator class.

It creates a
> separation between "iterator protocol" (which is implemented by
> __next__) and "generator protocol" (which is written in the body of a
> function with 'yield' in it).
>

terminology messing me up here -- I understood the "iterator protocol" top
mean the __iter__ and __next__ -- and a generator satisfies that protocol.
Is there a "generator protocol" that means somethign different?

Maybe that's what this whole sub-thread is about:

I never thought there was such a thing as a "generator protocol", and I
don't see why there should be.

-Chris


-- 

Christopher Barker, Ph.D.
Oceanographer

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