with_column supports SQL expression (#1284)

Author: milenkovicm

python/datafusion/dataframe.py

@@ -521,11 +521,12 @@ def parse_sql_expr(self, expr: str) -> Expr:
         """
         return Expr(self.df.parse_sql_expr(expr))
 
-    def with_column(self, name: str, expr: Expr) -> DataFrame:
+    def with_column(self, name: str, expr: Expr | str) -> DataFrame:
         """Add an additional column to the DataFrame.
 
         The ``expr`` must be an :class:`~datafusion.expr.Expr` constructed with
-        :func:`datafusion.col` or :func:`datafusion.lit`.
+        :func:`datafusion.col` or :func:`datafusion.lit`, or a SQL expression
+        string that will be parsed against the DataFrame schema.
 
         Example::
 
@@ -539,6 +540,8 @@ def with_column(self, name: str, expr: Expr) -> DataFrame:
         Returns:
             DataFrame with the new column.
         """
+        expr = self.parse_sql_expr(expr) if isinstance(expr, str) else expr
+
         return DataFrame(self.df.with_column(name, ensure_expr(expr)))
 
     def with_columns(

python/tests/test_dataframe.py

@@ -477,8 +477,8 @@ def test_tail(df):
     assert result.column(2) == pa.array([8])
 
 
-def test_with_column(df):
-    df = df.with_column("c", column("a") + column("b"))
+def test_with_column_sql_expression(df):
+    df = df.with_column("c", "a + b")
 
     # execute and collect the first (and only) batch
     result = df.collect()[0]
@@ -492,11 +492,19 @@ def test_with_column(df):
     assert result.column(2) == pa.array([5, 7, 9])
 
 
-def test_with_column_invalid_expr(df):
-    with pytest.raises(
-        TypeError, match=r"Use col\(\)/column\(\) or lit\(\)/literal\(\)"
-    ):
-        df.with_column("c", "a")
+def test_with_column(df):
+    df = df.with_column("c", column("a") + column("b"))
+
+    # execute and collect the first (and only) batch
+    result = df.collect()[0]
+
+    assert result.schema.field(0).name == "a"
+    assert result.schema.field(1).name == "b"
+    assert result.schema.field(2).name == "c"
+
+    assert result.column(0) == pa.array([1, 2, 3])
+    assert result.column(1) == pa.array([4, 5, 6])
+    assert result.column(2) == pa.array([5, 7, 9])
 
 
 def test_with_columns(df):