singleton for global context

Author: jsai28

python/datafusion/context.py

@@ -468,6 +468,8 @@ class SessionContext:
     See :ref:`user_guide_concepts` in the online documentation for more information.
     """
 
+    _global_instance = None
+
     def __init__(
         self,
         config: SessionConfig | None = None,
@@ -505,7 +507,10 @@ def global_ctx(cls) -> "SessionContextInternal":
         Returns:
             A `SessionContextInternal` object that corresponds to the global context
         """
-        return SessionContextInternal.global_ctx()
+        if cls._global_instance is None:
+            internal_ctx = SessionContextInternal.global_ctx()
+            cls._global_instance = internal_ctx
+        return cls._global_instance
 
     def enable_url_table(self) -> "SessionContext":
         """Control if local files can be queried as tables.

python/tests/test_context.py

@@ -30,8 +30,11 @@
     SQLOptions,
     column,
     literal,
+    udf,
 )
 
+from datafusion._internal import SessionContext as SessionContextInternal
+
 
 def test_create_context_no_args():
     SessionContext()
@@ -629,3 +632,32 @@ def test_sql_with_options_no_statements(ctx):
     options = SQLOptions().with_allow_statements(False)
     with pytest.raises(Exception, match="SetVariable"):
         ctx.sql_with_options(sql, options=options)
+
+
+def test_global_context_type():
+    ctx = SessionContext.global_ctx()
+    assert isinstance(ctx, SessionContextInternal)
+
+
+def test_global_context_is_singleton():
+    ctx1 = SessionContext.global_ctx()
+    ctx2 = SessionContext.global_ctx()
+    assert ctx1 is ctx2
+
+
+@pytest.fixture
+def batch():
+    return pa.RecordBatch.from_arrays(
+        [pa.array([4, 5, 6])],
+        names=["a"],
+    )
+
+
+def test_create_dataframe_with_global_ctx(batch):
+    ctx = SessionContext.global_ctx()
+
+    df = ctx.create_dataframe([[batch]])
+
+    result = df.collect()[0].column(0)
+
+    assert result == pa.array([4, 5, 6])