[LuisFigueroaG]

When a task fails, IMapIterator.next() raises Exception(value), where value is the ExceptionInfo, instead of the exception the task raised. Code iterating over imap()/imap_unordered() can't catch the error by its type (except ValueError never matches) and only gets a bare Exception wrapping the ExceptionInfo. apply_async().get() and map() already raise the original exception.

This raises value.exception, the same as ApplyResult.get().

With a task that raises ValueError('bad item 1'):

apply_async().get(): ValueError('bad item 1')
map():               ValueError('bad item 1')
imap() before:       Exception(<ExceptionInfo: ValueError('bad item 1')>)
imap() after:        ValueError('bad item 1')

Added a unit test for imap() and imap_unordered().

[auvipy]

is this a follow up of your previous PR?

[LuisFigueroaG]

Not a follow-up, they're independent. #475 keeps the Supervisor from crashing when a worker exits while an imap() is still pending (the iterator had no _write_to/_scheduled_for). This one is about what IMapIterator.next() raises when a task fails: it wrapped the ExceptionInfo in a plain Exception instead of raising the task's own exception like ApplyResult.get() does. I found both while looking at imap(), but either can go in first.