Add Session.read_ibis method

leanframe/core/session.py

@@ -45,6 +45,12 @@ def read_sql_table(self, table_name: str):
         #TODO: will crash if self._backend is None. 
         return leanframe.core.frame.DataFrame(self._backend.table(table_name)) # type: ignore
 
+    def read_ibis(self, table_expression: ibis_types.Table):
+        """Create a DataFrame from an Ibis table expression."""
+        import leanframe.core.frame
+
+        return leanframe.core.frame.DataFrame(table_expression)
+
     def DataFrame(self, data: ibis_types.Table | pandas.DataFrame):
         """Construct a DataFrame."""
         import leanframe.core.frame

tests/unit/session/test_read_ibis.py

@@ -0,0 +1,41 @@
+
+import ibis
+import pandas as pd
+import pytest
+from unittest.mock import MagicMock
+
+from leanframe.core import session
+
+@pytest.fixture
+def mock_backend():
+    return MagicMock()
+
+def test_read_ibis_returns_dataframe(mock_backend):
+    """Test that read_ibis returns a leanframe DataFrame."""
+    s = session.Session(mock_backend)
+    df = pd.DataFrame({'a': [1, 2, 3]})
+    t = ibis.memtable(df)
+
+    lf_df = s.read_ibis(t)
+
+    # Check that it is a leanframe DataFrame
+    # Note: importing DataFrame inside the function to avoid circular imports if any,
+    # though it should be fine at module level for type checking
+    from leanframe.core.frame import DataFrame
+    assert isinstance(lf_df, DataFrame)
+
+    # Check that the underlying data is correct
+    assert lf_df.to_ibis().equals(t)
+
+def test_read_ibis_with_complex_expression(mock_backend):
+    """Test read_ibis with a more complex ibis expression."""
+    s = session.Session(mock_backend)
+    df = pd.DataFrame({'a': [1, 2, 3], 'b': [4, 5, 6]})
+    t = ibis.memtable(df)
+    expr = t.mutate(c=t.a + t.b)
+
+    lf_df = s.read_ibis(expr)
+
+    from leanframe.core.frame import DataFrame
+    assert isinstance(lf_df, DataFrame)
+    assert lf_df.to_ibis().equals(expr)