Add support for next(cursor) - #1064
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This allows to call `next(cursor)`, which is guaranteed to never return None, making type checking simpler.
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This MR transforms the cursor from an iterable (supporting
iter()) to an iterator (supportingiter()andnext()).next(cursor)behaves likecursor.fetchone(), but its result isRow, notRow | None. That's because, if there is no row to fetch, it will raiseStopIteration.This makes simpler to write strictly typed code using the result when there is a 100% guarantee that a query will return a record (or will raise an exception), for example when fetching
count(*), which always returns a result even if the counted records are 0. The type checker is not aware of that, therefore you need to guard for None with anif, or anassert, or you need to do something horrible like(rec,) = cur.fetchall()in order to convince Mypy thatrecwill never be none.