Yury Selivanov <[email protected]> added the comment:
> ... result = list(await g(i) for i in range(3))
This is equivalent to this code:
async def ait():
for i in range(3):
v = await g(i)
yield v
result = list(ait())
Where 'ait' is an async generator function. You can't iterate it with the
regular 'for x in ...' syntax, and you can't pass it to functions that expect a
synchronous iterator (such as 'list').
Similarly, with synchronous code:
a = (i for i in range(3))
a[0]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'generator' object is not subscriptable
where '(' for ... ')' is another syntax for defining a synchronous generator.
> ... result = [await g(i) for i in range(3)]
This is equivalent to this code:
result = []
for i in range(3):
v = await g(i)
result.append(v)
I agree that PEP 530 is a bit vague about this and can be updated. I'll take a
look into that.
Perhaps we can make the "TypeError: 'async_generator' object is not iterable"
error message a bit clearer. Any ideas to improve it are welcome.
> I would say that the first case should either behave as a second one, or
> raise a syntax error.
No, but we can improve error messages.
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