fix: remove sessions' backend stack

Author: jakelorocco

mellea/stdlib/session.py

@@ -176,7 +176,6 @@ def __init__(self, backend: Backend, ctx: Context | None = None):
         """
         self.backend = backend
         self.ctx: Context = ctx if ctx is not None else SimpleContext()
-        self._backend_stack: list[Backend] = []
         self._session_logger = FancyLogger.get_logger()
         self._context_token = None
 
@@ -192,29 +191,8 @@ def __exit__(self, exc_type, exc_val, exc_tb):
             _context_session.reset(self._context_token)
             self._context_token = None
 
-    def _push_model_state(self, new_backend: Backend):
-        """The backend used within a `Context` can be temporarily changed. This method changes the model's backend, while saving the current settings in the `self._backend_stack`."""
-        self._backend_stack.append(self.backend)
-        self.backend = new_backend
-
-    def _pop_model_state(self) -> bool:
-        """Pops the model state.
-
-        The backend and model options used within a `Context` can be temporarily changed by pushing and popping from the model state.
-        This function restores the model's previous backend and model_opts from the `self._backend_stack`.
-
-        Question: should this logic be moved into context? I really want to keep `Session` as simple as possible... see true motivation in the docstring for the class.
-        """
-        try:
-            b = self._backend_stack.pop()
-            self.backend = b
-            return True
-        except Exception:
-            return False
-
     def __copy__(self):
         new = MelleaSession(backend=self.backend, ctx=self.ctx)
-        new._backend_stack = self._backend_stack.copy()
         new._session_logger = self._session_logger
         # Explicitly don't copy over the _context_token.
 
@@ -250,7 +228,6 @@ def reset(self):
     def cleanup(self) -> None:
         """Clean up session resources."""
         self.reset()
-        self._backend_stack.clear()
         if hasattr(self.backend, "close"):
             self.backend.close()  # type: ignore
 

test/stdlib_basics/test_session.py

@@ -125,30 +125,5 @@ def test_session_copy_with_context_ops(m_session):
     assert m1.ctx.previous_node.previous_node is m_session.ctx
     assert m2.ctx.previous_node.previous_node is m_session.ctx
 
-def test_session_copy_with_backend_stack(m_session):
-    # Assert expected values from cloning.
-    m1 = m_session.clone()
-    assert m1.backend is m_session.backend
-    assert m1._session_logger is m_session._session_logger
-    assert m1._backend_stack is not m_session._backend_stack
-
-    # Assert that pushing to a backend stack doesn't change it for sessions previously cloned from it.
-    new_backend = OllamaModelBackend()
-    m_session._push_model_state(new_backend=new_backend)
-    assert len(m_session._backend_stack) == 1
-    assert len(m1._backend_stack) == 0
-    assert m1.backend is not m_session.backend
-
-    # Assert that newly cloned sessions don't cause errors with changes to the backend stack.
-    m2 = m_session.clone()
-    assert len(m2._backend_stack) == 1
-
-    # They should still be different lists.
-    assert m2._backend_stack is not m_session._backend_stack
-    assert m2._pop_model_state()
-    assert len(m2._backend_stack) == 0
-    assert len(m_session._backend_stack) == 1
-    assert m2.backend is m1.backend
-
 if __name__ == "__main__":
     pytest.main([__file__])