How do I get both the rowcount and the instances of an SQLAlchemy ORM Query in a single roundtrip to the database?

If I call query.all(), I get a standard list, which I can get the len() of, but that requires loading the whole resultset in memory at once.

If I call iter(query), I get back a standard python generator, with no access to the .rowcount of the underlying ResultProxy.

If I call query.count() then iter(query) I'm doing two roundtrips of a potentially expensive query to the database.

if I managed to get hold of a ResultProxy for a Query, that would give me the .rowcount, then I could use Query.instances() to get the same generator that Query.__iter__() would give me.

But is there a convenient way of getting at the ResultProxy of a Query other than repeating what Query.__iter__() and Query._execute_and_instances() do? Seems rather inconvenient.

Notice

As mentioned by This answer (thanks @terminus), getting the ResultProxy.rowcount might or might not be useful, and is explicitly warned against in SQLAlchemy documentation for pure "select" statements.

That said, in the case of psycopg2, the .rowcount of the underlying cursor is documented to return the correct number of records returned by any query, even "SELECT" queries, unless you're using the stream_results=True option (thanks @SuperShoot).