Removed docstrings on tests.

doc/source/whatsnew/v3.0.0.rst

@@ -1156,7 +1156,6 @@ Reshaping
 - Bug in :meth:`DataFrame.unstack` producing incorrect results when manipulating empty :class:`DataFrame` with an :class:`ExtentionDtype` (:issue:`59123`)
 - Bug in :meth:`concat` where concatenating DataFrame and Series with ``ignore_index = True`` drops the series name (:issue:`60723`, :issue:`56257`)
 - Bug in :func:`melt` where calling with duplicate column names in ``id_vars`` raised a misleading ``AttributeError`` (:issue:`61475`)
-- Bug in :meth:`DataFrame.merge` where the result of a merge does not contain any metadata or flag information from the inputs to the merge. (:issue:`28283`)
 - Bug in :meth:`DataFrame.merge` where user-provided suffixes could result in duplicate column names if the resulting names matched existing columns. Now raises a :class:`MergeError` in such cases. (:issue:`61402`)
 - Bug in :meth:`DataFrame.merge` with :class:`CategoricalDtype` columns incorrectly raising ``RecursionError`` (:issue:`56376`)
 - Bug in :meth:`DataFrame.merge` with a ``float32`` index incorrectly casting the index to ``float64`` (:issue:`41626`)

pandas/core/reshape/merge.py

@@ -1139,21 +1139,13 @@ def get_result(self) -> DataFrame:
 
  result = self._reindex_and_concat(join_index, left_indexer, right_indexer)
 
- # Is this call to __finalize__ really necessary?
- result = result.__finalize__(
- types.SimpleNamespace(input_objs=[self.left, self.right]),
- method=self._merge_type,
- )
-
  if self.indicator:
  result = self._indicator_post_merge(result)
 
  self._maybe_add_join_keys(result, left_indexer, right_indexer)
 
  self._maybe_restore_index_levels(result)
 
- # __finalize is responsible for copying the metadata from the inputs to merge
- # to the result.
  return result.__finalize__(
  types.SimpleNamespace(input_objs=[self.left, self.right]), method="merge"
  )
@@ -1175,8 +1167,7 @@ def _indicator_pre_merge(
  self, left: DataFrame, right: DataFrame
  ) -> tuple[DataFrame, DataFrame]:
  """
- Add one indicator column to each of the left and right inputs to a
- merge operation.
+ Add one indicator column to each of the left and right inputs.
 
  These columns are used to produce another column in the output of the
  merge, indicating for each row of the output whether it was produced

pandas/tests/generic/test_finalize.py

@@ -691,30 +691,24 @@ def test_finalize_frame_series_name():
  "cross",
  ],
 )
-def test_merge_sets_duplication_allowance_flag(
+def test_merge_correctly_sets_duplication_allowance_flag(
  how: MergeHow,
  allow_on_left: bool,
  allow_on_right: bool,
 ):
  """Check that DataFrame.merge correctly sets the allow_duplicate_labels flag
  on its result.
-
- The flag on the result should be set to true if and only if both arguments
- to merge have their flags set to True.
  """
- # Arrange
  left = pd.DataFrame({"test": [1]}).set_flags(allows_duplicate_labels=allow_on_left)
  right = pd.DataFrame({"test": [1]}).set_flags(
  allows_duplicate_labels=allow_on_right,
  )
 
- # Act
  if not how == "cross":
  result = left.merge(right, how=how, on="test")
  else:
  result = left.merge(right, how=how)
 
- # Assert
  expected_duplication_allowance = allow_on_left and allow_on_right
  assert result.flags.allows_duplicate_labels == expected_duplication_allowance
 
@@ -723,64 +717,44 @@ def test_merge_sets_duplication_allowance_flag(
  ["allow_on_left", "allow_on_right"],
  [(False, False), (False, True), (True, False), (True, True)],
 )
-def test_merge_asof_sets_duplication_allowance_flag(
+def test_merge_asof_correctly_sets_duplication_allowance_flag(
  allow_on_left: bool,
  allow_on_right: bool,
 ):
- """Check that pandas.merge_asof correctly sets the allow_duplicate_labels flag
- on its result.
-
- The flag on the result should be set to true if and only if both arguments
- to merge_asof have their flags set to True.
- """
- # Arrange
  left = pd.DataFrame({"test": [1]}).set_flags(allows_duplicate_labels=allow_on_left)
  right = pd.DataFrame({"test": [1]}).set_flags(
  allows_duplicate_labels=allow_on_right,
  )
 
- # Act
  result = pd.merge_asof(left, right)
 
- # Assert
  expected_duplication_allowance = allow_on_left and allow_on_right
  assert result.flags.allows_duplicate_labels == expected_duplication_allowance
 
 
 def test_merge_propagates_metadata_from_equal_input_metadata():
- """Check that pandas.merge sets the metadata of its result to a deep copy of
- the metadata from its left input, if the metadata from both inputs are equal.
- """
- # Arrange
  metadata = {"a": 2}
  left = pd.DataFrame({"test": [1]})
  left.attrs = metadata
  right = pd.DataFrame({"test": [1]})
  right.attrs = metadata.copy()
 
- # Act
  result = left.merge(right, how="inner", on="test")
 
- # Assert
  assert result.attrs == metadata
+ # Verify that merge deep-copies the attr dictionary.
  left.attrs = {"b": 3}
  assert result.attrs == metadata
 
 
 def test_merge_does_not_propagate_metadata_from_unequal_input_metadata():
- """Check that the metadata for the result of pandas.merge is empty if the
- metadata for both inputs to pandas.merge are not equal.
- """
- # Arrange
  left = pd.DataFrame({"test": [1]})
  left.attrs = {"a": 2}
  right = pd.DataFrame({"test": [1]})
  right.attrs = {"b": 3}
 
- # Act
  result = left.merge(right, how="inner", on="test")
 
- # Assert
  assert result.attrs == {}
 
 
@@ -804,19 +778,6 @@ def test_merge_does_not_propagate_metadata_if_one_input_has_no_metadata(
  right: pd.DataFrame,
  expected: dict,
 ):
- """Check that if the metadata for one input to pandas.merge is empty, the result
- of merge has the same metadata as the other input.
-
- (empty) (A) (A) (empty) (empty) (empty)
- | | | | | |
- --> merge <-- --> merge <-- --> merge <--
- | | |
- (empty) (empty) (empty)
- """
- # Arrange
-
- # Act
  result = left.merge(right, how="inner", on="test")
 
- # Assert
  assert result.attrs == expected