sqlalchemy easy way to insert or update?

I have a sequence of new objects. They all look like similar to this:

Foo(pk_col1=x, pk_col2=y, val='bar')

Some of those are Foo that exist (i.e. only val differs from the row in the db) and should generate update queries. The others should generate inserts.

I can think of a few ways of doing this, the best being:

pk_cols = Foo.table.primary_key.keys()
for f1 in foos:
    f2 = Foo.get([getattr(f1, c) for c in pk_cols])
    if f2 is not None:
        f2.val = f1.val # update
        # XXX do we need to do session.add(f2) 
        # (or at least keep f2 alive until after the commit?)
    else:
        session.add(f1) # insert

 session.commit()

Is there an easier way?