validate result_type kwarg

Author: jreback

pandas/core/apply.py

@@ -39,6 +39,10 @@ def __init__(self, obj, func, broadcast, raw, reduce, result_type,
  self.args = args or ()
  self.kwds = kwds or {}
 
+ if result_type not in [None, 'reduce', 'broadcast', 'expand']:
+ raise ValueError("invalid value for result_type, must be one "
+ "of {None, 'reduce', 'broadcast', 'expand'}")
+
  if broadcast is not None:
  warnings.warn("The broadcast argument is deprecated and will "
  "be removed in a future version. You can specify "

pandas/io/formats/style.py

@@ -510,7 +510,7 @@ def _apply(self, func, axis=0, subset=None, **kwargs):
  data = self.data.loc[subset]
  if axis is not None:
  result = data.apply(func, axis=axis,
- result_type='infer', **kwargs)
+ result_type='expand', **kwargs)
  result.columns = data.columns
  else:
  result = func(data, **kwargs)

pandas/tests/frame/test_apply.py

@@ -750,6 +750,18 @@ def test_result_type(self):
  expected.columns = columns
  assert_frame_equal(result, expected)
 
+ @pytest.mark.parametrize("result_type", ['foo', 1])
+ def test_result_type_error(self, result_type):
+ # allowed result_type
+ df = DataFrame(
+ np.tile(np.arange(3, dtype='int64'), 6).reshape(6, -1) + 1,
+ columns=['A', 'B', 'C'])
+
+ with pytest.raises(ValueError):
+ df.apply(lambda x: [1, 2, 3],
+ axis=1,
+ result_type=result_type)
+
  @pytest.mark.parametrize(
  "box",
  [lambda x: list(x),