Add deregister methods to SessionContext for UDFs and object stores

Expose upstream DataFusion deregister methods (deregister_udf, deregister_udaf,
deregister_udwf, deregister_udtf, deregister_object_store) in both the Rust
PyO3 bindings and Python wrappers, closing the gap identified in #1457.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: timsaucer

crates/core/src/context.rs

@@ -439,6 +439,20 @@ impl PySessionContext {
         Ok(())
     }
 
+    /// Deregister an object store with the given url
+    #[pyo3(signature = (scheme, host=None))]
+    pub fn deregister_object_store(
+        &self,
+        scheme: &str,
+        host: Option<&str>,
+    ) -> PyDataFusionResult<()> {
+        let host = host.unwrap_or("");
+        let url_string = format!("{scheme}{host}");
+        let url = Url::parse(&url_string).unwrap();
+        self.ctx.runtime_env().deregister_object_store(&url)?;
+        Ok(())
+    }
+
     #[allow(clippy::too_many_arguments)]
     #[pyo3(signature = (name, path, table_partition_cols=vec![],
     file_extension=".parquet",
@@ -492,6 +506,10 @@ impl PySessionContext {
         self.ctx.register_udtf(&name, func);
     }
 
+    pub fn deregister_udtf(&self, name: &str) {
+        self.ctx.deregister_udtf(name);
+    }
+
     #[pyo3(signature = (query, options=None, param_values=HashMap::default(), param_strings=HashMap::default()))]
     pub fn sql_with_options(
         &self,
@@ -975,16 +993,28 @@ impl PySessionContext {
         Ok(())
     }
 
+    pub fn deregister_udf(&self, name: &str) {
+        self.ctx.deregister_udf(name);
+    }
+
     pub fn register_udaf(&self, udaf: PyAggregateUDF) -> PyResult<()> {
         self.ctx.register_udaf(udaf.function);
         Ok(())
     }
 
+    pub fn deregister_udaf(&self, name: &str) {
+        self.ctx.deregister_udaf(name);
+    }
+
     pub fn register_udwf(&self, udwf: PyWindowUDF) -> PyResult<()> {
         self.ctx.register_udwf(udwf.function);
         Ok(())
     }
 
+    pub fn deregister_udwf(&self, name: &str) {
+        self.ctx.deregister_udwf(name);
+    }
+
     #[pyo3(signature = (name="datafusion"))]
     pub fn catalog(&self, py: Python, name: &str) -> PyResult<Py<PyAny>> {
         let catalog = self.ctx.catalog(name).ok_or(PyKeyError::new_err(format!(

python/datafusion/context.py

@@ -568,6 +568,15 @@ def register_object_store(
         """
         self.ctx.register_object_store(schema, store, host)
 
+    def deregister_object_store(self, schema: str, host: str | None = None) -> None:
+        """Remove an object store from the session.
+
+        Args:
+            schema: The data source schema (e.g. ``"s3://"``).
+            host: URL for the host (e.g. bucket name).
+        """
+        self.ctx.deregister_object_store(schema, host)
+
     def register_listing_table(
         self,
         name: str,
@@ -894,6 +903,14 @@ def register_udtf(self, func: TableFunction) -> None:
         """Register a user defined table function."""
         self.ctx.register_udtf(func._udtf)
 
+    def deregister_udtf(self, name: str) -> None:
+        """Remove a user-defined table function from the session.
+
+        Args:
+            name: Name of the UDTF to deregister.
+        """
+        self.ctx.deregister_udtf(name)
+
     def register_record_batches(
         self, name: str, partitions: list[list[pa.RecordBatch]]
     ) -> None:
@@ -1105,14 +1122,38 @@ def register_udf(self, udf: ScalarUDF) -> None:
         """Register a user-defined function (UDF) with the context."""
         self.ctx.register_udf(udf._udf)
 
+    def deregister_udf(self, name: str) -> None:
+        """Remove a user-defined scalar function from the session.
+
+        Args:
+            name: Name of the UDF to deregister.
+        """
+        self.ctx.deregister_udf(name)
+
     def register_udaf(self, udaf: AggregateUDF) -> None:
         """Register a user-defined aggregation function (UDAF) with the context."""
         self.ctx.register_udaf(udaf._udaf)
 
+    def deregister_udaf(self, name: str) -> None:
+        """Remove a user-defined aggregate function from the session.
+
+        Args:
+            name: Name of the UDAF to deregister.
+        """
+        self.ctx.deregister_udaf(name)
+
     def register_udwf(self, udwf: WindowUDF) -> None:
         """Register a user-defined window function (UDWF) with the context."""
         self.ctx.register_udwf(udwf._udwf)
 
+    def deregister_udwf(self, name: str) -> None:
+        """Remove a user-defined window function from the session.
+
+        Args:
+            name: Name of the UDWF to deregister.
+        """
+        self.ctx.deregister_udwf(name)
+
     def catalog(self, name: str = "datafusion") -> Catalog:
         """Retrieve a catalog by name."""
         return Catalog(self.ctx.catalog(name))

python/tests/test_context.py

@@ -351,6 +351,126 @@ def test_deregister_table(ctx, database):
     assert public.names() == {"csv1", "csv2"}
 
 
+def test_deregister_udf():
+    ctx = SessionContext()
+    from datafusion import udf
+
+    is_null = udf(
+        lambda x: x.is_null(),
+        [pa.float64()],
+        pa.bool_(),
+        volatility="immutable",
+        name="my_is_null",
+    )
+    ctx.register_udf(is_null)
+
+    # Verify it works
+    df = ctx.from_pydict({"a": [1.0, None]})
+    ctx.register_table("t", df.into_view())
+    result = ctx.sql("SELECT my_is_null(a) FROM t").collect()
+    assert result[0].column(0) == pa.array([False, True])
+
+    # Deregister and verify it's gone
+    ctx.deregister_udf("my_is_null")
+    with pytest.raises(RuntimeError):
+        ctx.sql("SELECT my_is_null(a) FROM t").collect()
+
+
+def test_deregister_udaf():
+    import pyarrow.compute as pc
+
+    ctx = SessionContext()
+    from datafusion import Accumulator, udaf
+
+    class MySum(Accumulator):
+        def __init__(self):
+            self._sum = 0.0
+
+        def update(self, values: pa.Array) -> None:
+            self._sum += pc.sum(values).as_py()
+
+        def merge(self, states: list[pa.Array]) -> None:
+            self._sum += pc.sum(states[0]).as_py()
+
+        def state(self) -> list:
+            return [self._sum]
+
+        def evaluate(self) -> pa.Scalar:
+            return self._sum
+
+    my_sum = udaf(
+        MySum,
+        [pa.float64()],
+        pa.float64(),
+        [pa.float64()],
+        volatility="immutable",
+        name="my_sum",
+    )
+    ctx.register_udaf(my_sum)
+    df = ctx.from_pydict({"a": [1.0, 2.0, 3.0]})
+    ctx.register_table("t", df.into_view())
+
+    result = ctx.sql("SELECT my_sum(a) FROM t").collect()
+    assert result[0].column(0) == pa.array([6.0])
+
+    ctx.deregister_udaf("my_sum")
+    with pytest.raises(RuntimeError):
+        ctx.sql("SELECT my_sum(a) FROM t").collect()
+
+
+def test_deregister_udwf():
+    ctx = SessionContext()
+    from datafusion import udwf
+    from datafusion.user_defined import WindowEvaluator
+
+    class MyRowNumber(WindowEvaluator):
+        def __init__(self):
+            self._row = 0
+
+        def evaluate_all(self, values, num_rows):
+            return pa.array(list(range(1, num_rows + 1)), type=pa.uint64())
+
+    my_row_number = udwf(
+        MyRowNumber,
+        [pa.float64()],
+        pa.uint64(),
+        volatility="immutable",
+        name="my_row_number",
+    )
+    ctx.register_udwf(my_row_number)
+    df = ctx.from_pydict({"a": [1.0, 2.0, 3.0]})
+    ctx.register_table("t", df.into_view())
+
+    result = ctx.sql("SELECT my_row_number(a) OVER () FROM t").collect()
+    assert result[0].column(0) == pa.array([1, 2, 3], type=pa.uint64())
+
+    ctx.deregister_udwf("my_row_number")
+    with pytest.raises(RuntimeError):
+        ctx.sql("SELECT my_row_number(a) OVER () FROM t").collect()
+
+
+def test_deregister_udtf():
+    import pyarrow.dataset as ds
+
+    ctx = SessionContext()
+    from datafusion import Table, udtf
+
+    class MyTable:
+        def __call__(self):
+            batch = pa.RecordBatch.from_pydict({"x": [1, 2, 3]})
+            return Table(ds.dataset([batch]))
+
+    my_table = udtf(MyTable(), "my_table")
+    ctx.register_udtf(my_table)
+
+    result = ctx.sql("SELECT * FROM my_table()").collect()
+    assert result[0].column(0) == pa.array([1, 2, 3])
+
+    ctx.deregister_udtf("my_table")
+    with pytest.raises(RuntimeError):
+        ctx.sql("SELECT * FROM my_table()").collect()
+
+
 def test_register_table_from_dataframe(ctx):
     df = ctx.from_pydict({"a": [1, 2]})
     ctx.register_table("df_tbl", df)