Nick Coghlan <ncogh...@gmail.com> added the comment:
I realised that even without modifying the compiler first, I could illustrate
the proposed `yield from` based resolution for the comprehension case by way of
explicit yield from clauses:
```
def get_gen_result(gen, inputs):
try:
yield_value = next(gen)
for send_value in inputs:
print(f"Received: {yield_value}; Sending: {send_value}")
yield_value = gen.send(send_value)
except StopIteration as exc:
return exc.value
raise RuntimeError("Failed to exhaust generator")
def example():
comp1 = yield from [str((yield x)) for x in ('1st', '2nd')]
comp2 = yield from [int((yield x)) for x in ('3rd', '4th')]
return comp1, comp2
>>> result = get_gen_result(example(), range(4))
Received: 1st; Sending: 0
Received: 2nd; Sending: 1
Received: 3rd; Sending: 2
Received: 4th; Sending: 3
>>> result
(['0', '1'], [2, 3])
```
So if we decided to make yield-in-a-comprehension imply the use of yield from,
we'd only need:
- DeprecationWarning in 3.7 to say "this is going to imply 'yield from
(comprehension)' in 3.8+"
- making the 'yield from' implicit in 3.8 (thus ensuring that comprehensions
always return the correct container type, even when they include yield
expressions)
----------
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue10544>
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