ENH: Move SettingWithCopyError to error/__init__.py per GH27656 (#47151)

* ENH: Move SettingWithCopyError to error/__init__.py per GH27656

* ENH: add exception to test_exception_importable

Author: dataxerik

doc/source/reference/testing.rst

@@ -41,6 +41,7 @@ Exceptions and warnings
    errors.ParserError
    errors.ParserWarning
    errors.PerformanceWarning
+   errors.SettingWithCopyError
    errors.SpecificationError
    errors.UnsortedIndexError
    errors.UnsupportedFunctionCall

doc/source/user_guide/indexing.rst

@@ -1885,7 +1885,7 @@ chained indexing expression, you can set the :ref:`option <options>`
 ``mode.chained_assignment`` to one of these values:
 
 * ``'warn'``, the default, means a ``SettingWithCopyWarning`` is printed.
-* ``'raise'`` means pandas will raise a ``SettingWithCopyException``
+* ``'raise'`` means pandas will raise a ``SettingWithCopyError``
   you have to deal with.
 * ``None`` will suppress the warnings entirely.
 
@@ -1953,7 +1953,7 @@ Last, the subsequent example will **not** work at all, and so should be avoided:
    >>> dfd.loc[0]['a'] = 1111
    Traceback (most recent call last)
         ...
-   SettingWithCopyException:
+   SettingWithCopyError:
         A value is trying to be set on a copy of a slice from a DataFrame.
         Try using .loc[row_index,col_indexer] = value instead
 

doc/source/whatsnew/v1.5.0.rst

@@ -151,7 +151,7 @@ Other enhancements
 - A :class:`errors.PerformanceWarning` is now thrown when using ``string[pyarrow]`` dtype with methods that don't dispatch to ``pyarrow.compute`` methods (:issue:`42613`)
 - Added ``numeric_only`` argument to :meth:`Resampler.sum`, :meth:`Resampler.prod`, :meth:`Resampler.min`, :meth:`Resampler.max`, :meth:`Resampler.first`, and :meth:`Resampler.last` (:issue:`46442`)
 - ``times`` argument in :class:`.ExponentialMovingWindow` now accepts ``np.timedelta64`` (:issue:`47003`)
-- :class:`DataError` and :class:`SpecificationError` are now exposed in ``pandas.errors`` (:issue:`27656`)
+- :class:`DataError`, :class:`SpecificationError`, and :class:`SettingWithCopyError` are now exposed in ``pandas.errors`` (:issue:`27656`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_150.notable_bug_fixes:

pandas/core/common.py

@@ -58,10 +58,6 @@
     from pandas import Index
 
 
-class SettingWithCopyError(ValueError):
-    pass
-
-
 class SettingWithCopyWarning(Warning):
     pass
 

pandas/core/generic.py

@@ -69,6 +69,7 @@
 from pandas.errors import (
     AbstractMethodError,
     InvalidIndexError,
+    SettingWithCopyError,
 )
 from pandas.util._decorators import (
     deprecate_kwarg,
@@ -3949,7 +3950,7 @@ def _check_setitem_copy(self, t="setting", force=False):
             )
 
         if value == "raise":
-            raise com.SettingWithCopyError(t)
+            raise SettingWithCopyError(t)
         elif value == "warn":
             warnings.warn(t, com.SettingWithCopyWarning, stacklevel=find_stack_level())
 

pandas/errors/__init__.py

@@ -267,3 +267,24 @@ class SpecificationError(Exception):
     >>> df.groupby('A').agg(['min', 'min']) # doctest: +SKIP
     ... # SpecificationError: nested renamer is not supported
     """
+
+
+class SettingWithCopyError(ValueError):
+    """
+    Exception is raised when trying to set on a copied slice from a dataframe and
+    the mode.chained_assignment is set to 'raise.' This can happen unintentionally
+    when chained indexing.
+
+    For more information, see 'Evaluation order matters' on
+    https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html
+
+    For more information, see 'Indexing view versus copy' on
+    https://pandas.pydata.org/pandas-docs/stable/user_guide/indexing.html
+
+    Examples
+    --------
+    >>> pd.options.mode.chained_assignment = 'raise'
+    >>> df = pd.DataFrame({'A': [1, 1, 1, 2, 2]}, columns=['A'])
+    >>> df.loc[0:3]['A'] = 'a' # doctest: +SKIP
+    ... # SettingWithCopyError: A value is trying to be set on a copy of a...
+    """

pandas/tests/frame/indexing/test_indexing.py

@@ -8,7 +8,10 @@
 import pytest
 
 from pandas._libs import iNaT
-from pandas.errors import InvalidIndexError
+from pandas.errors import (
+    InvalidIndexError,
+    SettingWithCopyError,
+)
 import pandas.util._test_decorators as td
 
 from pandas.core.dtypes.common import is_integer
@@ -27,7 +30,6 @@
     notna,
 )
 import pandas._testing as tm
-import pandas.core.common as com
 
 # We pass through a TypeError raised by numpy
 _slice_msg = "slice indices must be integers or None or have an __index__ method"
@@ -303,7 +305,7 @@ def test_setitem(self, float_frame):
         smaller = float_frame[:2]
 
         msg = r"\nA value is trying to be set on a copy of a slice from a DataFrame"
-        with pytest.raises(com.SettingWithCopyError, match=msg):
+        with pytest.raises(SettingWithCopyError, match=msg):
             smaller["col10"] = ["1", "2"]
 
         assert smaller["col10"].dtype == np.object_
@@ -546,7 +548,7 @@ def test_fancy_getitem_slice_mixed(self, float_frame, float_string_frame):
         assert np.shares_memory(sliced["C"]._values, float_frame["C"]._values)
 
         msg = r"\nA value is trying to be set on a copy of a slice from a DataFrame"
-        with pytest.raises(com.SettingWithCopyError, match=msg):
+        with pytest.raises(SettingWithCopyError, match=msg):
             sliced.loc[:, "C"] = 4.0
 
         assert (float_frame["C"] == 4).all()
@@ -1003,7 +1005,7 @@ def test_iloc_row_slice_view(self, using_array_manager):
         assert np.shares_memory(df[2], subset[2])
 
         msg = r"\nA value is trying to be set on a copy of a slice from a DataFrame"
-        with pytest.raises(com.SettingWithCopyError, match=msg):
+        with pytest.raises(SettingWithCopyError, match=msg):
             subset.loc[:, 2] = 0.0
 
         exp_col = original[2].copy()
@@ -1046,7 +1048,7 @@ def test_iloc_col_slice_view(self, using_array_manager):
 
             # and that we are setting a copy
             msg = r"\nA value is trying to be set on a copy of a slice from a DataFrame"
-            with pytest.raises(com.SettingWithCopyError, match=msg):
+            with pytest.raises(SettingWithCopyError, match=msg):
                 subset.loc[:, 8] = 0.0
 
             assert (df[8] == 0).all()

pandas/tests/frame/indexing/test_xs.py

@@ -3,6 +3,8 @@
 import numpy as np
 import pytest
 
+from pandas.errors import SettingWithCopyError
+
 from pandas import (
     DataFrame,
     Index,
@@ -12,7 +14,6 @@
     concat,
 )
 import pandas._testing as tm
-import pandas.core.common as com
 
 from pandas.tseries.offsets import BDay
 
@@ -120,7 +121,7 @@ def test_xs_view(self, using_array_manager):
             # INFO(ArrayManager) with ArrayManager getting a row as a view is
             # not possible
             msg = r"\nA value is trying to be set on a copy of a slice from a DataFrame"
-            with pytest.raises(com.SettingWithCopyError, match=msg):
+            with pytest.raises(SettingWithCopyError, match=msg):
                 dm.xs(2)[:] = 20
             assert not (dm.xs(2) == 20).any()
         else:
@@ -183,7 +184,7 @@ def test_xs_setting_with_copy_error(self, multiindex_dataframe_random_data):
         # setting this will give a SettingWithCopyError
         # as we are trying to write a view
         msg = "A value is trying to be set on a copy of a slice from a DataFrame"
-        with pytest.raises(com.SettingWithCopyError, match=msg):
+        with pytest.raises(SettingWithCopyError, match=msg):
             result[:] = 10
 
     def test_xs_setting_with_copy_error_multiple(self, four_level_index_dataframe):
@@ -194,7 +195,7 @@ def test_xs_setting_with_copy_error_multiple(self, four_level_index_dataframe):
         # setting this will give a SettingWithCopyError
         # as we are trying to write a view
         msg = "A value is trying to be set on a copy of a slice from a DataFrame"
-        with pytest.raises(com.SettingWithCopyError, match=msg):
+        with pytest.raises(SettingWithCopyError, match=msg):
             result[:] = 10
 
     @pytest.mark.parametrize("key, level", [("one", "second"), (["one"], ["second"])])

pandas/tests/indexing/multiindex/test_chaining_and_caching.py

@@ -1,6 +1,7 @@
 import numpy as np
 import pytest
 
+from pandas.errors import SettingWithCopyError
 import pandas.util._test_decorators as td
 
 from pandas import (
@@ -9,7 +10,6 @@
     Series,
 )
 import pandas._testing as tm
-import pandas.core.common as com
 
 
 def test_detect_chained_assignment():
@@ -30,7 +30,7 @@ def test_detect_chained_assignment():
     zed = DataFrame(events, index=["a", "b"], columns=multiind)
 
     msg = "A value is trying to be set on a copy of a slice from a DataFrame"
-    with pytest.raises(com.SettingWithCopyError, match=msg):
+    with pytest.raises(SettingWithCopyError, match=msg):
         zed["eyes"]["right"].fillna(value=555, inplace=True)
 
 

pandas/tests/indexing/multiindex/test_setitem.py

@@ -1,6 +1,7 @@
 import numpy as np
 import pytest
 
+from pandas.errors import SettingWithCopyError
 import pandas.util._test_decorators as td
 
 import pandas as pd
@@ -14,7 +15,6 @@
     notna,
 )
 import pandas._testing as tm
-import pandas.core.common as com
 
 
 def assert_equal(a, b):
@@ -491,7 +491,7 @@ def test_frame_setitem_copy_raises(multiindex_dataframe_random_data):
     # will raise/warn as its chained assignment
     df = multiindex_dataframe_random_data.T
     msg = "A value is trying to be set on a copy of a slice from a DataFrame"
-    with pytest.raises(com.SettingWithCopyError, match=msg):
+    with pytest.raises(SettingWithCopyError, match=msg):
         df["foo"]["one"] = 2
 
 
@@ -500,7 +500,7 @@ def test_frame_setitem_copy_no_write(multiindex_dataframe_random_data):
     expected = frame
     df = frame.copy()
     msg = "A value is trying to be set on a copy of a slice from a DataFrame"
-    with pytest.raises(com.SettingWithCopyError, match=msg):
+    with pytest.raises(SettingWithCopyError, match=msg):
         df["foo"]["one"] = 2
 
     result = df