DEPR Enforce ewm.vol deprecation (pandas-dev#48841)

Author: mroeschke

doc/source/whatsnew/v2.0.0.rst

@@ -212,6 +212,7 @@ Removal of prior version deprecations/changes
 - Removed deprecated :meth:`Categorical.replace`, use :meth:`Series.replace` instead (:issue:`44929`)
 - Removed the ``numeric_only`` keyword from :meth:`Categorical.min` and :meth:`Categorical.max` in favor of ``skipna`` (:issue:`48821`)
 - Removed :func:`is_extension_type` in favor of :func:`is_extension_array_dtype` (:issue:`29457`)
+- Removed ``.ExponentialMovingWindow.vol`` (:issue:`39220`)
 - Removed :meth:`Index.get_value` and :meth:`Index.set_value` (:issue:`33907`, :issue:`28621`)
 - Removed :meth:`Series.slice_shift` and :meth:`DataFrame.slice_shift` (:issue:`37601`)
 - Remove :meth:`DataFrameGroupBy.pad` and :meth:`DataFrameGroupBy.backfill` (:issue:`45076`)

pandas/core/window/ewm.py

@@ -4,7 +4,6 @@
 from functools import partial
 from textwrap import dedent
 from typing import TYPE_CHECKING
-import warnings
 
 import numpy as np
 
@@ -21,7 +20,6 @@
 
 from pandas.compat.numpy import function as nv
 from pandas.util._decorators import doc
-from pandas.util._exceptions import find_stack_level
 
 from pandas.core.dtypes.common import (
     is_datetime64_ns_dtype,
@@ -653,17 +651,6 @@ def std(self, bias: bool = False, numeric_only: bool = False, *args, **kwargs):
             )
         return zsqrt(self.var(bias=bias, numeric_only=numeric_only, **kwargs))
 
-    def vol(self, bias: bool = False, *args, **kwargs):
-        warnings.warn(
-            (
-                "vol is deprecated will be removed in a future version. "
-                "Use std instead."
-            ),
-            FutureWarning,
-            stacklevel=find_stack_level(),
-        )
-        return self.std(bias, *args, **kwargs)
-
     @doc(
         template_header,
         create_section_header("Parameters"),

pandas/tests/window/test_ewm.py

@@ -170,14 +170,6 @@ def test_ewm_getitem_attributes_retained(arg, adjust, ignore_na):
     assert result == expected
 
 
-def test_ewm_vol_deprecated():
-    ser = Series(range(1))
-    with tm.assert_produces_warning(FutureWarning):
-        result = ser.ewm(com=0.1).vol()
-    expected = ser.ewm(com=0.1).std()
-    tm.assert_series_equal(result, expected)
-
-
 def test_ewma_times_adjust_false_raises():
     # GH 40098
     with pytest.raises(