code: def _nodes_from_tuples(self, tups):
      s = set()
      for tup in tups:
          s.update(tup)
      return s
  
imports: from sqlalchemy import exc
  from sqlalchemy.testing import assert_raises
  from sqlalchemy.testing import eq_
  from sqlalchemy.testing import fixtures
  from sqlalchemy.testing.util import conforms_partial_ordering
  from sqlalchemy.util import topological
label_desc: Use image node_id 3 for calling the DependencySortTest obj's underlying member method code with example usage: obj._nodes_from_tuples(tups) and returns: s