fix agg with one element func list given arg and kwargs

Author: luke

pandas/core/apply.py

@@ -130,6 +130,16 @@ def __init__(
             def f(x):
                 return func(x, *args, **kwargs)
 
+        # GH 50642
+        elif (
+            (args or kwargs)
+            and not isinstance(func, str)
+            and is_one_element_callable_list(func)
+        ):
+
+            def f(x):
+                return func[0](x, *args, **kwargs)
+
         else:
             f = func
 
@@ -1206,6 +1216,11 @@ def is_multi_agg_with_relabel(**kwargs) -> bool:
     )
 
 
+def is_one_element_callable_list(func: AggFuncType | None) -> bool:
+    # GH 50642
+    return isinstance(func, list) and len(func) == 1
+
+
 def normalize_keyword_aggregation(
     kwargs: dict,
 ) -> tuple[dict, list[str], npt.NDArray[np.intp]]:

pandas/tests/apply/test_frame_apply_relabeling.py

@@ -95,3 +95,15 @@ def test_agg_namedtuple():
         index=pd.Index(["foo", "bar", "cat"]),
     )
     tm.assert_frame_equal(result, expected)
+
+
+def test_agg_given_one_element_func_list_arg_kwargs():
+    # GH 50642
+    df = pd.DataFrame({"x": [1, 2, 3]})
+
+    def foo(x, a, b=2):
+        return x + a + b
+
+    result = df.agg([foo], 0, 1, b=2)
+    expected = pd.DataFrame({"x": [4, 5, 6]})
+    tm.assert_frame_equal(result, expected)