It seems that select() does indeed support arbitrary iterables through the use of PySequence_Fast().

The commit where this was introduced, by Brett Cannon from 2003 (62dba4c2775adfb5a5a97ca012a3ab00c4e28597), doesn't seems to have intended this though: "select.select() now accepts a sequence (as defined by PySequence_Fast()) for its first three arguments."

However, regardless of whether this is intentional, it appears that this has been this way for a very long time. So it seems to me that we should document this behavior, as suggested here, since any change to this would be an unacceptable backwards-incompatibility.