TYP: DataFrame.(index|columns) and Series.index

doc/source/whatsnew/v1.0.0.rst

@@ -687,7 +687,6 @@ Other API changes
 - :meth:`Series.str.__iter__` was deprecated and will be removed in future releases (:issue:`28277`).
 - Added ``<NA>`` to the list of default NA values for :meth:`read_csv` (:issue:`30821`)
 
-
 .. _whatsnew_100.api.documentation:
 
 Documentation Improvements

doc/source/whatsnew/v1.1.0.rst

@@ -55,7 +55,12 @@ Other API changes
 - :meth:`Series.describe` will now show distribution percentiles for ``datetime`` dtypes, statistics ``first`` and ``last``
   will now be ``min`` and ``max`` to match with numeric dtypes in :meth:`DataFrame.describe` (:issue:`30164`)
 -
--
+
+Backwards incompatible API changes
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+- :meth:`DataFrame.swaplevels` now raises a  ``TypeError`` if the axis is not a :class:`MultiIndex`.
+  Previously a ``AttributeError`` was raised (:issue:`31126`)
+
 
 .. ---------------------------------------------------------------------------
 

pandas/core/frame.py

@@ -38,7 +38,7 @@
 
 from pandas._config import get_option
 
-from pandas._libs import algos as libalgos, lib
+from pandas._libs import algos as libalgos, lib, properties
 from pandas._typing import Axes, Axis, Dtype, FilePathOrBuffer, Level, Renamer
 from pandas.compat import PY37
 from pandas.compat._optional import import_optional_dependency
@@ -91,8 +91,10 @@
 )
 from pandas.core.dtypes.generic import (
     ABCDataFrame,
+    ABCDatetimeIndex,
     ABCIndexClass,
     ABCMultiIndex,
+    ABCPeriodIndex,
     ABCSeries,
 )
 from pandas.core.dtypes.missing import isna, notna
@@ -394,6 +396,7 @@ class DataFrame(NDFrame):
     2  7  8  9
     """
 
+    _internal_names_set = {"columns", "index"} | NDFrame._internal_names_set
     _typ = "dataframe"
 
     @property
@@ -5290,9 +5293,15 @@ def swaplevel(self, i=-2, j=-1, axis=0) -> "DataFrame":
         result = self.copy()
 
         axis = self._get_axis_number(axis)
+
+        if not isinstance(result._get_axis(axis), ABCMultiIndex):  # pragma: no cover
+            raise TypeError("Can only swap levels on a hierarchical axis.")
+
         if axis == 0:
+            assert isinstance(result.index, ABCMultiIndex)
             result.index = result.index.swaplevel(i, j)
         else:
+            assert isinstance(result.columns, ABCMultiIndex)
             result.columns = result.columns.swaplevel(i, j)
         return result
 
@@ -5319,8 +5328,10 @@ def reorder_levels(self, order, axis=0) -> "DataFrame":
         result = self.copy()
 
         if axis == 0:
+            assert isinstance(result.index, ABCMultiIndex)
             result.index = result.index.reorder_levels(order)
         else:
+            assert isinstance(result.columns, ABCMultiIndex)
             result.columns = result.columns.reorder_levels(order)
         return result
 
@@ -8344,8 +8355,10 @@ def to_timestamp(self, freq=None, how="start", axis=0, copy=True) -> "DataFrame"
 
         axis = self._get_axis_number(axis)
         if axis == 0:
+            assert isinstance(self.index, (ABCDatetimeIndex, ABCPeriodIndex))
             new_data.set_axis(1, self.index.to_timestamp(freq=freq, how=how))
         elif axis == 1:
+            assert isinstance(self.columns, (ABCDatetimeIndex, ABCPeriodIndex))
             new_data.set_axis(0, self.columns.to_timestamp(freq=freq, how=how))
         else:  # pragma: no cover
             raise AssertionError(f"Axis must be 0 or 1. Got {axis}")
@@ -8378,8 +8391,10 @@ def to_period(self, freq=None, axis=0, copy=True) -> "DataFrame":
 
         axis = self._get_axis_number(axis)
         if axis == 0:
+            assert isinstance(self.index, ABCDatetimeIndex)
             new_data.set_axis(1, self.index.to_period(freq=freq))
         elif axis == 1:
+            assert isinstance(self.columns, ABCDatetimeIndex)
             new_data.set_axis(0, self.columns.to_period(freq=freq))
         else:  # pragma: no cover
             raise AssertionError(f"Axis must be 0 or 1. Got {axis}")
@@ -8482,6 +8497,15 @@ def isin(self, values) -> "DataFrame":
                 self.columns,
             )
 
+    # ----------------------------------------------------------------------
+    # Add index and columns
+    index: "Index" = properties.AxisProperty(
+        axis=1, doc="The index (row labels) of the DataFrame."
+    )
+    columns: "Index" = properties.AxisProperty(
+        axis=0, doc="The column labels of the DataFrame."
+    )
+
     # ----------------------------------------------------------------------
     # Add plotting methods to DataFrame
     plot = CachedAccessor("plot", pandas.plotting.PlotAccessor)

pandas/core/generic.py

@@ -30,7 +30,7 @@
 
 from pandas._config import config
 
-from pandas._libs import Timestamp, iNaT, lib, properties
+from pandas._libs import Timestamp, iNaT, lib
 from pandas._typing import (
     Axis,
     Dtype,
@@ -333,18 +333,6 @@ def _setup_axes(cls, axes: List[str], docs: Dict[str, str]) -> None:
         cls._info_axis_number = info_axis
         cls._info_axis_name = axes[info_axis]
 
-        # setup the actual axis
-        def set_axis(a, i):
-            setattr(cls, a, properties.AxisProperty(i, docs.get(a, a)))
-            cls._internal_names_set.add(a)
-
-        if axes_are_reversed:
-            for i, a in cls._AXIS_NAMES.items():
-                set_axis(a, 1 - i)
-        else:
-            for i, a in cls._AXIS_NAMES.items():
-                set_axis(a, i)
-
     def _construct_axes_dict(self, axes=None, **kwargs):
         """Return an axes dictionary for myself."""
         d = {a: self._get_axis(a) for a in (axes or self._AXIS_ORDERS)}
@@ -5083,6 +5071,7 @@ def __finalize__(
                 self.attrs[name] = other.attrs[name]
             # For subclasses using _metadata.
             for name in self._metadata:
+                assert isinstance(name, str)
                 object.__setattr__(self, name, getattr(other, name, None))
         return self
 

pandas/core/reshape/pivot.py

@@ -134,13 +134,13 @@ def pivot_table(
         table = agged.unstack(to_unstack)
 
     if not dropna:
-        if table.index.nlevels > 1:
+        if isinstance(table.index, MultiIndex):
             m = MultiIndex.from_arrays(
                 cartesian_product(table.index.levels), names=table.index.names
             )
             table = table.reindex(m, axis=0)
 
-        if table.columns.nlevels > 1:
+        if isinstance(table.columns, MultiIndex):
             m = MultiIndex.from_arrays(
                 cartesian_product(table.columns.levels), names=table.columns.names
             )
@@ -373,7 +373,7 @@ def _generate_marginal_results_without_values(
 ):
     if len(cols) > 0:
         # need to "interleave" the margins
-        margin_keys = []
+        margin_keys: Union[List, Index] = []
 
         def _all_key():
             if len(cols) == 1:

pandas/core/series.py

@@ -22,7 +22,7 @@
 
 from pandas._config import get_option
 
-from pandas._libs import index as libindex, lib, reshape, tslibs
+from pandas._libs import index as libindex, lib, properties, reshape, tslibs
 from pandas._typing import Label
 from pandas.compat.numpy import function as nv
 from pandas.util._decorators import Appender, Substitution
@@ -46,6 +46,8 @@
 from pandas.core.dtypes.generic import (
     ABCDataFrame,
     ABCDatetimeIndex,
+    ABCMultiIndex,
+    ABCPeriodIndex,
     ABCSeries,
     ABCSparseArray,
 )
@@ -176,6 +178,7 @@ class Series(base.IndexOpsMixin, generic.NDFrame):
 
     _name: Optional[Hashable]
     _metadata: List[str] = ["name"]
+    _internal_names_set = {"index"} | generic.NDFrame._internal_names_set
     _accessors = {"dt", "cat", "str", "sparse"}
     _deprecations = (
         base.IndexOpsMixin._deprecations
@@ -3347,6 +3350,7 @@ def swaplevel(self, i=-2, j=-1, copy=True) -> "Series":
         Series
             Series with levels swapped in MultiIndex.
         """
+        assert isinstance(self.index, ABCMultiIndex)
         new_index = self.index.swaplevel(i, j)
         return self._constructor(self._values, index=new_index, copy=copy).__finalize__(
             self
@@ -3371,6 +3375,7 @@ def reorder_levels(self, order) -> "Series":
             raise Exception("Can only reorder levels on a hierarchical axis.")
 
         result = self.copy()
+        assert isinstance(result.index, ABCMultiIndex)
         result.index = result.index.reorder_levels(order)
         return result
 
@@ -4448,6 +4453,7 @@ def to_timestamp(self, freq=None, how="start", copy=True) -> "Series":
         if copy:
             new_values = new_values.copy()
 
+        assert isinstance(self.index, (ABCDatetimeIndex, ABCPeriodIndex))
         new_index = self.index.to_timestamp(freq=freq, how=how)
         return self._constructor(new_values, index=new_index).__finalize__(self)
 
@@ -4472,9 +4478,16 @@ def to_period(self, freq=None, copy=True) -> "Series":
         if copy:
             new_values = new_values.copy()
 
+        assert isinstance(self.index, ABCDatetimeIndex)
         new_index = self.index.to_period(freq=freq)
         return self._constructor(new_values, index=new_index).__finalize__(self)
 
+    # ----------------------------------------------------------------------
+    # Add index and columns
+    index: "Index" = properties.AxisProperty(
+        axis=0, doc="The index (axis labels) of the Series."
+    )
+
     # ----------------------------------------------------------------------
     # Accessor Methods
     # ----------------------------------------------------------------------

pandas/io/formats/format.py

@@ -57,10 +57,13 @@
     is_timedelta64_dtype,
 )
 from pandas.core.dtypes.generic import (
+    ABCDatetimeIndex,
     ABCIndexClass,
     ABCMultiIndex,
+    ABCPeriodIndex,
     ABCSeries,
     ABCSparseArray,
+    ABCTimedeltaIndex,
 )
 from pandas.core.dtypes.missing import isna, notna
 
@@ -295,6 +298,9 @@ def _get_footer(self) -> str:
         footer = ""
 
         if getattr(self.series.index, "freq", None) is not None:
+            assert isinstance(
+                self.series.index, (ABCDatetimeIndex, ABCPeriodIndex, ABCTimedeltaIndex)
+            )
             footer += "Freq: {freq}".format(freq=self.series.index.freqstr)
 
         if self.name is not False and name is not None:

pandas/tests/test_multilevel.py

@@ -957,6 +957,10 @@ def test_swaplevel(self):
         exp = self.frame.swaplevel("first", "second").T
         tm.assert_frame_equal(swapped, exp)
 
+        msg = "Can only swap levels on a hierarchical axis."
+        with pytest.raises(TypeError, match=msg):
+            DataFrame(range(3)).swaplevel()
+
     def test_reorder_levels(self):
         result = self.ymd.reorder_levels(["month", "day", "year"])
         expected = self.ymd.swaplevel(0, 1).swaplevel(1, 2)