DEPR: deprecate fastpath keyword in Index constructors (pandas-dev#23110)

Author: jorisvandenbossche

doc/source/whatsnew/v0.24.0.txt

@@ -734,6 +734,7 @@ Deprecations
   many ``Series``, ``Index`` or 1-dimensional ``np.ndarray``, or alternatively, only scalar values. (:issue:`21950`)
 - :meth:`FrozenNDArray.searchsorted` has deprecated the ``v`` parameter in favor of ``value`` (:issue:`14645`)
 - :func:`DatetimeIndex.shift` and :func:`PeriodIndex.shift` now accept ``periods`` argument instead of ``n`` for consistency with :func:`Index.shift` and :func:`Series.shift`. Using ``n`` throws a deprecation warning (:issue:`22458`, :issue:`22912`)
+- The ``fastpath`` keyword of the different Index constructors is deprecated (:issue:`23110`).
 
 .. _whatsnew_0240.prior_deprecations:
 

pandas/core/indexes/base.py

@@ -262,13 +262,17 @@ def _outer_indexer(self, left, right):
     str = CachedAccessor("str", StringMethods)
 
     def __new__(cls, data=None, dtype=None, copy=False, name=None,
-                fastpath=False, tupleize_cols=True, **kwargs):
+                fastpath=None, tupleize_cols=True, **kwargs):
 
         if name is None and hasattr(data, 'name'):
             name = data.name
 
-        if fastpath:
-            return cls._simple_new(data, name)
+        if fastpath is not None:
+            warnings.warn("The 'fastpath' keyword is deprecated, and will be "
+                          "removed in a future version.",
+                          FutureWarning, stacklevel=2)
+            if fastpath:
+                return cls._simple_new(data, name)
 
         from .range import RangeIndex
 

pandas/core/indexes/category.py

@@ -1,4 +1,5 @@
 import operator
+import warnings
 
 import numpy as np
 from pandas._libs import index as libindex
@@ -87,10 +88,14 @@ class CategoricalIndex(Index, accessor.PandasDelegate):
     _attributes = ['name']
 
     def __new__(cls, data=None, categories=None, ordered=None, dtype=None,
-                copy=False, name=None, fastpath=False):
-
-        if fastpath:
-            return cls._simple_new(data, name=name, dtype=dtype)
+                copy=False, name=None, fastpath=None):
+
+        if fastpath is not None:
+            warnings.warn("The 'fastpath' keyword is deprecated, and will be "
+                          "removed in a future version.",
+                          FutureWarning, stacklevel=2)
+            if fastpath:
+                return cls._simple_new(data, name=name, dtype=dtype)
 
         if name is None and hasattr(data, 'name'):
             name = data.name

pandas/core/indexes/numeric.py

@@ -1,3 +1,5 @@
+import warnings
+
 import numpy as np
 from pandas._libs import index as libindex
 from pandas.core.dtypes.common import (
@@ -34,10 +36,14 @@ class NumericIndex(Index):
     _is_numeric_dtype = True
 
     def __new__(cls, data=None, dtype=None, copy=False, name=None,
-                fastpath=False):
-
-        if fastpath:
-            return cls._simple_new(data, name=name)
+                fastpath=None):
+
+        if fastpath is not None:
+            warnings.warn("The 'fastpath' keyword is deprecated, and will be "
+                          "removed in a future version.",
+                          FutureWarning, stacklevel=2)
+            if fastpath:
+                return cls._simple_new(data, name=name)
 
         # is_scalar, generators handled in coerce_to_ndarray
         data = cls._coerce_to_ndarray(data)

pandas/core/indexes/period.py

@@ -268,7 +268,7 @@ def __contains__(self, key):
 
     @cache_readonly
     def _int64index(self):
-        return Int64Index(self.asi8, name=self.name, fastpath=True)
+        return Int64Index._simple_new(self.asi8, name=self.name)
 
     @property
     def values(self):

pandas/core/indexes/range.py

@@ -1,6 +1,7 @@
 import operator
 from datetime import timedelta
 from sys import getsizeof
+import warnings
 
 import numpy as np
 
@@ -62,10 +63,14 @@ class RangeIndex(Int64Index):
     _engine_type = libindex.Int64Engine
 
     def __new__(cls, start=None, stop=None, step=None,
-                dtype=None, copy=False, name=None, fastpath=False):
+                dtype=None, copy=False, name=None, fastpath=None):
 
-        if fastpath:
-            return cls._simple_new(start, stop, step, name=name)
+        if fastpath is not None:
+            warnings.warn("The 'fastpath' keyword is deprecated, and will be "
+                          "removed in a future version.",
+                          FutureWarning, stacklevel=2)
+            if fastpath:
+                return cls._simple_new(start, stop, step, name=name)
 
         cls._validate_dtype(dtype)
 
@@ -168,7 +173,7 @@ def _data(self):
 
     @cache_readonly
     def _int64index(self):
-        return Int64Index(self._data, name=self.name, fastpath=True)
+        return Int64Index._simple_new(self._data, name=self.name)
 
     def _get_data_as_items(self):
         """ return a list of tuples of start, stop, step """
@@ -256,8 +261,8 @@ def tolist(self):
     @Appender(_index_shared_docs['_shallow_copy'])
     def _shallow_copy(self, values=None, **kwargs):
         if values is None:
-            return RangeIndex(name=self.name, fastpath=True,
-                              **dict(self._get_data_as_items()))
+            return RangeIndex._simple_new(
+                name=self.name, **dict(self._get_data_as_items()))
         else:
             kwargs.setdefault('name', self.name)
             return self._int64index._shallow_copy(values, **kwargs)
@@ -267,8 +272,8 @@ def copy(self, name=None, deep=False, dtype=None, **kwargs):
         self._validate_dtype(dtype)
         if name is None:
             name = self.name
-        return RangeIndex(name=name, fastpath=True,
-                          **dict(self._get_data_as_items()))
+        return RangeIndex._simple_new(
+            name=name, **dict(self._get_data_as_items()))
 
     def _minmax(self, meth):
         no_steps = len(self) - 1
@@ -368,7 +373,7 @@ def intersection(self, other):
         tmp_start = first._start + (second._start - first._start) * \
             first._step // gcd * s
         new_step = first._step * second._step // gcd
-        new_index = RangeIndex(tmp_start, int_high, new_step, fastpath=True)
+        new_index = RangeIndex._simple_new(tmp_start, int_high, new_step)
 
         # adjust index to limiting interval
         new_index._start = new_index._min_fitting_element(int_low)
@@ -546,7 +551,7 @@ def __getitem__(self, key):
             stop = self._start + self._step * stop
             step = self._step * step
 
-            return RangeIndex(start, stop, step, name=self.name, fastpath=True)
+            return RangeIndex._simple_new(start, stop, step, name=self.name)
 
         # fall back to Int64Index
         return super_getitem(key)
@@ -559,12 +564,12 @@ def __floordiv__(self, other):
                 start = self._start // other
                 step = self._step // other
                 stop = start + len(self) * step
-                return RangeIndex(start, stop, step, name=self.name,
-                                  fastpath=True)
+                return RangeIndex._simple_new(
+                    start, stop, step, name=self.name)
             if len(self) == 1:
                 start = self._start // other
-                return RangeIndex(start, start + 1, 1, name=self.name,
-                                  fastpath=True)
+                return RangeIndex._simple_new(
+                    start, start + 1, 1, name=self.name)
         return self._int64index // other
 
     @classmethod

pandas/tests/indexes/test_base.py

@@ -2530,3 +2530,32 @@ def test_index_subclass_constructor_wrong_kwargs(index_maker):
     # GH #19348
     with tm.assert_raises_regex(TypeError, 'unexpected keyword argument'):
         index_maker(foo='bar')
+
+
+def test_deprecated_fastpath():
+
+    with tm.assert_produces_warning(FutureWarning):
+        idx = pd.Index(
+            np.array(['a', 'b'], dtype=object), name='test', fastpath=True)
+
+    expected = pd.Index(['a', 'b'], name='test')
+    tm.assert_index_equal(idx, expected)
+
+    with tm.assert_produces_warning(FutureWarning):
+        idx = pd.Int64Index(
+            np.array([1, 2, 3], dtype='int64'), name='test', fastpath=True)
+
+    expected = pd.Index([1, 2, 3], name='test', dtype='int64')
+    tm.assert_index_equal(idx, expected)
+
+    with tm.assert_produces_warning(FutureWarning):
+        idx = pd.RangeIndex(0, 5, 2, name='test', fastpath=True)
+
+    expected = pd.RangeIndex(0, 5, 2, name='test')
+    tm.assert_index_equal(idx, expected)
+
+    with tm.assert_produces_warning(FutureWarning):
+        idx = pd.CategoricalIndex(['a', 'b', 'c'], name='test', fastpath=True)
+
+    expected = pd.CategoricalIndex(['a', 'b', 'c'], name='test')
+    tm.assert_index_equal(idx, expected)