ENH: move SpecificationError to error/__init__.py

doc/source/reference/testing.rst

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

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` now exposed in ``pandas.errors`` (:issue:`27656`)
+- :class:`DataError` and :class:`SpecificationError` are now exposed in ``pandas.errors`` (:issue:`27656`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_150.notable_bug_fixes:

pandas/core/apply.py

@@ -33,7 +33,10 @@
     Axis,
     NDFrameT,
 )
-from pandas.errors import DataError
+from pandas.errors import (
+    DataError,
+    SpecificationError,
+)
 from pandas.util._decorators import cache_readonly
 from pandas.util._exceptions import find_stack_level
 
@@ -51,10 +54,7 @@
 )
 
 from pandas.core.algorithms import safe_sort
-from pandas.core.base import (
-    SelectionMixin,
-    SpecificationError,
-)
+from pandas.core.base import SelectionMixin
 import pandas.core.common as com
 from pandas.core.construction import (
     create_series_with_explicit_dtype,

pandas/core/base.py

@@ -176,10 +176,6 @@ def __setattr__(self, key: str, value):
         object.__setattr__(self, key, value)
 
 
-class SpecificationError(Exception):
-    pass
-
-
 class SelectionMixin(Generic[NDFrameT]):
     """
     mixin implementing the selection & aggregation interface on a group-like

pandas/core/groupby/generic.py

@@ -37,6 +37,7 @@
     Manager2D,
     SingleManager,
 )
+from pandas.errors import SpecificationError
 from pandas.util._decorators import (
     Appender,
     Substitution,
@@ -68,7 +69,6 @@
     reconstruct_func,
     validate_func_kwargs,
 )
-from pandas.core.base import SpecificationError
 import pandas.core.common as com
 from pandas.core.construction import create_series_with_explicit_dtype
 from pandas.core.frame import DataFrame

pandas/errors/__init__.py

@@ -244,3 +244,26 @@ class DataError(Exception):
     Or, it can be raised when trying to apply a function to a non-numerical
     column on a rolling window.
     """
+
+
+class SpecificationError(Exception):
+    """
+    Exception raised in two scenarios. The first way is calling agg on a
+    Dataframe or Series using a nested renamer (dict-of-dict).
+    The second way is calling agg on a Dataframe with duplicated functions
+    names without assigning column name.
+
+    Examples
+    --------
+    >>> df = pd.DataFrame({'A': [1, 1, 1, 2, 2],
+    ...                    'B': range(5),
+    ...                    'C': range(5)})
+    >>> df.groupby('A').B.agg({'foo': 'count'}) # doctest: +SKIP
+    ... # SpecificationError: nested renamer is not supported
+
+    >>> df.groupby('A').agg({'B': {'foo': ['sum', 'max']}}) # doctest: +SKIP
+    ... # SpecificationError: nested renamer is not supported
+
+    >>> df.groupby('A').agg(['min', 'min']) # doctest: +SKIP
+    ... # SpecificationError: nested renamer is not supported
+    """

pandas/tests/apply/test_invalid_arg.py

@@ -12,6 +12,8 @@
 import numpy as np
 import pytest
 
+from pandas.errors import SpecificationError
+
 from pandas import (
     Categorical,
     DataFrame,
@@ -20,7 +22,6 @@
     notna,
 )
 import pandas._testing as tm
-from pandas.core.base import SpecificationError
 
 
 @pytest.mark.parametrize("result_type", ["foo", 1])

pandas/tests/groupby/aggregate/test_aggregate.py

@@ -9,6 +9,8 @@
 import numpy as np
 import pytest
 
+from pandas.errors import SpecificationError
+
 from pandas.core.dtypes.common import is_integer_dtype
 
 import pandas as pd
@@ -21,7 +23,6 @@
     to_datetime,
 )
 import pandas._testing as tm
-from pandas.core.base import SpecificationError
 from pandas.core.groupby.grouper import Grouping
 
 

pandas/tests/groupby/aggregate/test_other.py

@@ -8,6 +8,8 @@
 import numpy as np
 import pytest
 
+from pandas.errors import SpecificationError
+
 import pandas as pd
 from pandas import (
     DataFrame,
@@ -19,7 +21,6 @@
     period_range,
 )
 import pandas._testing as tm
-from pandas.core.base import SpecificationError
 
 from pandas.io.formats.printing import pprint_thing
 

pandas/tests/groupby/test_groupby.py

@@ -6,7 +6,10 @@
 
 from pandas._libs import lib
 from pandas.compat import IS64
-from pandas.errors import PerformanceWarning
+from pandas.errors import (
+    PerformanceWarning,
+    SpecificationError,
+)
 
 import pandas as pd
 from pandas import (
@@ -24,7 +27,6 @@
 )
 import pandas._testing as tm
 from pandas.core.arrays import BooleanArray
-from pandas.core.base import SpecificationError
 import pandas.core.common as com
 from pandas.core.groupby.base import maybe_normalize_deprecated_kernels
 

pandas/tests/resample/test_resample_api.py

@@ -427,15 +427,15 @@ def test_agg():
 
     msg = "nested renamer is not supported"
     for t in cases:
-        with pytest.raises(pd.core.base.SpecificationError, match=msg):
+        with pytest.raises(pd.errors.SpecificationError, match=msg):
             t.aggregate({"A": {"mean": "mean", "sum": "sum"}})
 
     expected = pd.concat([a_mean, a_sum, b_mean, b_sum], axis=1)
     expected.columns = pd.MultiIndex.from_tuples(
         [("A", "mean"), ("A", "sum"), ("B", "mean2"), ("B", "sum2")]
     )
     for t in cases:
-        with pytest.raises(pd.core.base.SpecificationError, match=msg):
+        with pytest.raises(pd.errors.SpecificationError, match=msg):
             t.aggregate(
                 {
                     "A": {"mean": "mean", "sum": "sum"},
@@ -539,10 +539,10 @@ def test_agg_misc():
 
     # series like aggs
     for t in cases:
-        with pytest.raises(pd.core.base.SpecificationError, match=msg):
+        with pytest.raises(pd.errors.SpecificationError, match=msg):
             t["A"].agg({"A": ["sum", "std"]})
 
-        with pytest.raises(pd.core.base.SpecificationError, match=msg):
+        with pytest.raises(pd.errors.SpecificationError, match=msg):
             t["A"].agg({"A": ["sum", "std"], "B": ["mean", "std"]})
 
     # errors
@@ -588,17 +588,17 @@ def test_agg_nested_dicts():
 
     msg = "nested renamer is not supported"
     for t in cases:
-        with pytest.raises(pd.core.base.SpecificationError, match=msg):
+        with pytest.raises(pd.errors.SpecificationError, match=msg):
             t.aggregate({"r1": {"A": ["mean", "sum"]}, "r2": {"B": ["mean", "sum"]}})
 
     for t in cases:
 
-        with pytest.raises(pd.core.base.SpecificationError, match=msg):
+        with pytest.raises(pd.errors.SpecificationError, match=msg):
             t[["A", "B"]].agg(
                 {"A": {"ra": ["mean", "std"]}, "B": {"rb": ["mean", "std"]}}
             )
 
-        with pytest.raises(pd.core.base.SpecificationError, match=msg):
+        with pytest.raises(pd.errors.SpecificationError, match=msg):
             t.agg({"A": {"ra": ["mean", "std"]}, "B": {"rb": ["mean", "std"]}})
 
 

pandas/tests/test_errors.py

@@ -20,6 +20,7 @@
         "OptionError",
         "NumbaUtilError",
         "DataError",
+        "SpecificationError",
     ],
 )
 def test_exception_importable(exc):

pandas/tests/window/test_api.py

@@ -1,6 +1,8 @@
 import numpy as np
 import pytest
 
+from pandas.errors import SpecificationError
+
 from pandas import (
     DataFrame,
     Index,
@@ -13,7 +15,6 @@
     timedelta_range,
 )
 import pandas._testing as tm
-from pandas.core.base import SpecificationError
 
 
 def test_getitem(step):