From a040752a0d46a288605c48d7f90ec6d805d9c88b Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Mon, 19 Oct 2020 17:29:11 -0700
Subject: [PATCH 1/8] TYP: use @final in Index

---
 pandas/core/indexes/base.py | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index d1a52011a3ad7..947f2a1ad932b 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -17,6 +17,7 @@
     TypeVar,
     Union,
     cast,
+    final,
 )
 import warnings
 
@@ -1449,6 +1450,7 @@ def _sort_levels_monotonic(self):
         """
         return self
 
+    @final
     def _validate_index_level(self, level):
         """
         Validate index level.
@@ -2072,6 +2074,7 @@ def is_mixed(self) -> bool:
         )
         return self.inferred_type in ["mixed"]
 
+    @final
     def holds_integer(self) -> bool:
         """
         Whether the type is an integer type.
@@ -2333,6 +2336,7 @@ def unique(self, level=None):
         result = super().unique()
         return self._shallow_copy(result)
 
+    @final
     def drop_duplicates(self, keep="first"):
         """
         Return Index with duplicate values removed.
@@ -2503,6 +2507,7 @@ def __nonzero__(self):
     # --------------------------------------------------------------------
     # Set Operation Methods
 
+    @final
     def _get_reconciled_name_object(self, other):
         """
         If the result of a set operation will be self,
@@ -2514,6 +2519,7 @@ def _get_reconciled_name_object(self, other):
             return self.rename(name)
         return self
 
+    @final
     def _union_incompatible_dtypes(self, other, sort):
         """
         Casts this and other index to object dtype to allow the formation
@@ -2554,6 +2560,7 @@ def _can_union_without_object_cast(self, other) -> bool:
         """
         return type(self) is type(other) and is_dtype_equal(self.dtype, other.dtype)
 
+    @final
     def _validate_sort_keyword(self, sort):
         if sort not in [None, False]:
             raise ValueError(
@@ -2690,6 +2697,7 @@ def _union(self, other, sort):
 
         return self._shallow_copy(result)
 
+    @final
     def _wrap_setop_result(self, other, result):
         if isinstance(self, (ABCDatetimeIndex, ABCTimedeltaIndex)) and isinstance(
             result, np.ndarray
@@ -3100,6 +3108,7 @@ def _convert_tolerance(self, tolerance, target):
             raise ValueError("list-like tolerance size must match target index size")
         return tolerance
 
+    @final
     def _get_fill_indexer(
         self, target: "Index", method: str_t, limit=None, tolerance=None
     ) -> np.ndarray:
@@ -3119,6 +3128,7 @@ def _get_fill_indexer(
             indexer = self._filter_indexer_tolerance(target_values, indexer, tolerance)
         return indexer
 
+    @final
     def _get_fill_indexer_searchsorted(
         self, target: "Index", method: str_t, limit=None
     ) -> np.ndarray:
@@ -3152,6 +3162,7 @@ def _get_fill_indexer_searchsorted(
             indexer[indexer == len(self)] = -1
         return indexer
 
+    @final
     def _get_nearest_indexer(self, target: "Index", limit, tolerance) -> np.ndarray:
         """
         Get the indexer for the nearest index labels; requires an index with
@@ -3175,6 +3186,7 @@ def _get_nearest_indexer(self, target: "Index", limit, tolerance) -> np.ndarray:
             indexer = self._filter_indexer_tolerance(target_values, indexer, tolerance)
         return indexer
 
+    @final
     def _filter_indexer_tolerance(
         self,
         target: Union["Index", np.ndarray, ExtensionArray],
@@ -3198,6 +3210,7 @@ def _get_partial_string_timestamp_match_key(self, key):
         # GH#10331
         return key
 
+    @final
     def _validate_positional_slice(self, key: slice):
         """
         For positional indexing, a slice must have either int or None
@@ -3331,6 +3344,7 @@ def _convert_list_indexer(self, keyarr):
         """
         return None
 
+    @final
     def _invalid_indexer(self, form: str_t, key):
         """
         Consistent invalid indexer message.
@@ -3343,6 +3357,7 @@ def _invalid_indexer(self, form: str_t, key):
     # --------------------------------------------------------------------
     # Reindex Methods
 
+    @final
     def _can_reindex(self, indexer):
         """
         Check if we are allowing reindexing with this particular indexer.
@@ -3608,6 +3623,7 @@ def join(self, other, how="left", level=None, return_indexers=False, sort=False)
         else:
             return join_index
 
+    @final
     def _join_multi(self, other, how, return_indexers=True):
         from pandas.core.indexes.multi import MultiIndex
         from pandas.core.reshape.merge import restore_dropped_levels_multijoin
@@ -3687,6 +3703,7 @@ def _join_multi(self, other, how, return_indexers=True):
                 return result[0], result[2], result[1]
         return result
 
+    @final
     def _join_non_unique(self, other, how="left", return_indexers=False):
         from pandas.core.reshape.merge import get_join_indexers
 
@@ -4057,6 +4074,7 @@ def _string_data_error(cls, data):
             "to explicitly cast to a numeric type"
         )
 
+    @final
     def _coerce_scalar_to_index(self, item):
         """
         We need to coerce a scalar to a compat for our index type.
@@ -4087,6 +4105,7 @@ def _validate_fill_value(self, value):
         """
         return value
 
+    @final
     def _validate_scalar(self, value):
         """
         Check that this is a scalar value that we can use for setitem-like
@@ -4157,9 +4176,11 @@ def __contains__(self, key: Any) -> bool:
         except (OverflowError, TypeError, ValueError):
             return False
 
+    @final
     def __hash__(self):
         raise TypeError(f"unhashable type: {repr(type(self).__name__)}")
 
+    @final
     def __setitem__(self, key, value):
         raise TypeError("Index does not support mutable operations")
 
@@ -4200,6 +4221,7 @@ def __getitem__(self, key):
         else:
             return result
 
+    @final
     def _can_hold_identifiers_and_holds_name(self, name) -> bool:
         """
         Faster check for ``name in self`` when we know `name` is a Python
@@ -4353,6 +4375,7 @@ def equals(self, other: object) -> bool:
 
         return array_equivalent(self._values, other._values)
 
+    @final
     def identical(self, other) -> bool:
         """
         Similar to equals, but checks that object attributes and types are also equal.
@@ -4666,6 +4689,7 @@ def argsort(self, *args, **kwargs) -> np.ndarray:
 
         return result.argsort(*args, **kwargs)
 
+    @final
     def get_value(self, series: "Series", key):
         """
         Fast lookup of value from 1-dimensional ndarray.
@@ -4732,6 +4756,7 @@ def _get_values_for_loc(self, series: "Series", loc, key):
 
         return series.iloc[loc]
 
+    @final
     def set_value(self, arr, key, value):
         """
         Fast lookup of value from 1-dimensional ndarray.
@@ -4795,6 +4820,7 @@ def get_indexer_non_unique(self, target):
         indexer, missing = self._engine.get_indexer_non_unique(tgt_values)
         return ensure_platform_int(indexer), missing
 
+    @final
     def get_indexer_for(self, target, **kwargs):
         """
         Guaranteed return of an indexer even when non-unique.
@@ -4822,6 +4848,7 @@ def _index_as_unique(self):
         """
         return self.is_unique
 
+    @final
     def _maybe_promote(self, other: "Index"):
         """
         When dealing with an object-dtype Index and a non-object Index, see
@@ -4921,6 +4948,7 @@ def map(self, mapper, na_action=None):
         return Index(new_values, **attributes)
 
     # TODO: De-duplicate with map, xref GH#32349
+    @final
     def _transform_index(self, func, level=None) -> "Index":
         """
         Apply function to all values found in index.
@@ -5096,6 +5124,7 @@ def _maybe_cast_indexer(self, key):
             return com.cast_scalar_indexer(key)
         return key
 
+    @final
     def _validate_indexer(self, form: str_t, key, kind: str_t):
         """
         If we are positional indexer, validate that we have appropriate

From f7b96142847c07620ca9406bd22e022b1cdb197b Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Mon, 19 Oct 2020 17:43:45 -0700
Subject: [PATCH 2/8] TYP: use @final

---
 pandas/core/indexes/base.py | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 947f2a1ad932b..23d52bbfea426 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -446,6 +446,7 @@ def _simple_new(cls, values, name: Label = None):
     def _constructor(self):
         return type(self)
 
+    @final
     def _maybe_check_unique(self):
         """
         Check that an Index has no duplicates.
@@ -466,6 +467,7 @@ def _maybe_check_unique(self):
 
             raise DuplicateLabelError(msg)
 
+    @final
     def _format_duplicate_message(self):
         """
         Construct the DataFrame for a DuplicateLabelError.
@@ -495,6 +497,7 @@ def _format_duplicate_message(self):
     # --------------------------------------------------------------------
     # Index Internals Methods
 
+    @final
     def _get_attributes_dict(self):
         """
         Return an attributes dict for my class.
@@ -523,6 +526,7 @@ def _shallow_copy(self, values=None, name: Label = no_default):
         result._cache = self._cache
         return result
 
+    @final
     def is_(self, other) -> bool:
         """
         More flexible, faster check like ``is`` but that works through views.
@@ -553,12 +557,14 @@ def is_(self, other) -> bool:
         else:
             return self._id is other._id
 
+    @final
     def _reset_identity(self) -> None:
         """
         Initializes or resets ``_id`` attribute with new object.
         """
         self._id = _Identity(object())
 
+    @final
     def _cleanup(self):
         self._engine.clear_mapping()
 
@@ -618,6 +624,7 @@ def dtype(self):
         """
         return self._data.dtype
 
+    @final
     def ravel(self, order="C"):
         """
         Return an ndarray of the flattened values of the underlying data.
@@ -872,9 +879,11 @@ def copy(
             new_index = new_index.astype(dtype)
         return new_index
 
+    @final
     def __copy__(self, **kwargs):
         return self.copy(**kwargs)
 
+    @final
     def __deepcopy__(self, memo=None):
         """
         Parameters
@@ -1243,6 +1252,7 @@ def name(self, value):
         maybe_extract_name(value, None, type(self))
         self._name = value
 
+    @final
     def _validate_names(self, name=None, names=None, deep: bool = False) -> List[Label]:
         """
         Handles the quirks of having a singular 'name' parameter for general
@@ -1305,6 +1315,7 @@ def _set_names(self, values, level=None):
 
     names = property(fset=_set_names, fget=_get_names)
 
+    @final
     def set_names(self, names, level=None, inplace: bool = False):
         """
         Set Index or MultiIndex name.
@@ -1552,6 +1563,7 @@ def _get_level_values(self, level):
 
     get_level_values = _get_level_values
 
+    @final
     def droplevel(self, level=0):
         """
         Return index with requested level(s) removed.
@@ -2152,6 +2164,7 @@ def hasnans(self) -> bool:
         else:
             return False
 
+    @final
     def isna(self):
         """
         Detect missing values.
@@ -2209,6 +2222,7 @@ def isna(self):
 
     isnull = isna
 
+    @final
     def notna(self):
         """
         Detect existing (non-missing) values.
@@ -2487,15 +2501,19 @@ def __iadd__(self, other):
         # alias for __add__
         return self + other
 
+    @final
     def __and__(self, other):
         return self.intersection(other)
 
+    @final
     def __or__(self, other):
         return self.union(other)
 
+    @final
     def __xor__(self, other):
         return self.symmetric_difference(other)
 
+    @final
     def __nonzero__(self):
         raise ValueError(
             f"The truth value of a {type(self).__name__} is ambiguous. "
@@ -4395,6 +4413,7 @@ def identical(self, other) -> bool:
             and type(self) == type(other)
         )
 
+    @final
     def asof(self, label):
         """
         Return the label from the index, or, if not present, the previous one.
@@ -4583,6 +4602,7 @@ def sort_values(
         else:
             return sorted_index
 
+    @final
     def sort(self, *args, **kwargs):
         """
         Use sort_values instead.

From 031b2f8b8caed49fc3dea36cb2d74ff76e47ddbf Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Mon, 19 Oct 2020 17:50:53 -0700
Subject: [PATCH 3/8] TYP: use @final

---
 pandas/core/indexes/base.py | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 23d52bbfea426..f0cba13853518 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -4076,6 +4076,7 @@ def where(self, cond, other=None):
         return Index(values, dtype=dtype, name=self.name)
 
     # construction helpers
+    @final
     @classmethod
     def _scalar_data_error(cls, data):
         # We return the TypeError so that we can raise it from the constructor
@@ -4085,6 +4086,7 @@ def _scalar_data_error(cls, data):
             f"kind, {repr(data)} was passed"
         )
 
+    @final
     @classmethod
     def _string_data_error(cls, data):
         raise TypeError(
@@ -4517,6 +4519,7 @@ def asof_locs(self, where, mask):
 
         return result
 
+    @final
     def sort_values(
         self,
         return_indexer: bool = False,
@@ -4899,6 +4902,7 @@ def _is_comparable_dtype(self, dtype: DtypeObj) -> bool:
         """
         return True
 
+    @final
     def groupby(self, values) -> PrettyDict[Hashable, np.ndarray]:
         """
         Group the index labels by a given array of values.
@@ -5612,6 +5616,7 @@ def all(self):
         self._maybe_disable_logical_methods("all")
         return np.all(self.values)
 
+    @final
     def _maybe_disable_logical_methods(self, opname: str_t):
         """
         raise if this Index subclass does not support any or all.

From c9279613491bd5e471740d7e2d8d4c1039e146a6 Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Tue, 20 Oct 2020 08:51:37 -0700
Subject: [PATCH 4/8] TYP: use @final

---
 pandas/core/indexes/base.py | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index f0cba13853518..f34cc8a951853 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -1663,6 +1663,7 @@ def _get_grouper_for_level(self, mapper, level=None):
     # --------------------------------------------------------------------
     # Introspection Methods
 
+    @final
     @property
     def is_monotonic(self) -> bool:
         """
@@ -1777,6 +1778,7 @@ def has_duplicates(self) -> bool:
         """
         return not self.is_unique
 
+    @final
     def is_boolean(self) -> bool:
         """
         Check if the Index only consists of booleans.
@@ -1812,6 +1814,7 @@ def is_boolean(self) -> bool:
         """
         return self.inferred_type in ["boolean"]
 
+    @final
     def is_integer(self) -> bool:
         """
         Check if the Index only consists of integers.
@@ -1847,6 +1850,7 @@ def is_integer(self) -> bool:
         """
         return self.inferred_type in ["integer"]
 
+    @final
     def is_floating(self) -> bool:
         """
         Check if the Index is a floating type.
@@ -1890,6 +1894,7 @@ def is_floating(self) -> bool:
         """
         return self.inferred_type in ["floating", "mixed-integer-float", "integer-na"]
 
+    @final
     def is_numeric(self) -> bool:
         """
         Check if the Index only consists of numeric data.
@@ -1933,6 +1938,7 @@ def is_numeric(self) -> bool:
         """
         return self.inferred_type in ["integer", "floating"]
 
+    @final
     def is_object(self) -> bool:
         """
         Check if the Index is of the object dtype.
@@ -1973,6 +1979,7 @@ def is_object(self) -> bool:
         """
         return is_object_dtype(self.dtype)
 
+    @final
     def is_categorical(self) -> bool:
         """
         Check if the Index holds categorical data.
@@ -2016,6 +2023,7 @@ def is_categorical(self) -> bool:
         """
         return self.inferred_type in ["categorical"]
 
+    @final
     def is_interval(self) -> bool:
         """
         Check if the Index holds Interval objects.
@@ -2049,6 +2057,7 @@ def is_interval(self) -> bool:
         """
         return self.inferred_type in ["interval"]
 
+    @final
     def is_mixed(self) -> bool:
         """
         Check if the Index holds data with mixed data types.

From da2f1d467180dcc2b4d9f31d0b298145937ee122 Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Tue, 20 Oct 2020 09:02:40 -0700
Subject: [PATCH 5/8] TYP: use @final

---
 pandas/core/indexes/base.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index f34cc8a951853..7f87513d17e09 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -2157,6 +2157,7 @@ def _isnan(self):
             return values
 
     @cache_readonly
+    @final
     def _nan_idxs(self):
         if self._can_hold_na:
             return self._isnan.nonzero()[0]

From ee6ba1daa6d1a777a43bf5c61693fd76bc30c745 Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Fri, 30 Oct 2020 15:40:12 -0700
Subject: [PATCH 6/8] import final only im TYPE_CHECKING

---
 pandas/core/indexes/base.py | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 7f87513d17e09..1b190b18eac84 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -17,7 +17,6 @@
     TypeVar,
     Union,
     cast,
-    final,
 )
 import warnings
 
@@ -101,7 +100,12 @@
 )
 
 if TYPE_CHECKING:
+    from typing import final
+
     from pandas import MultiIndex, RangeIndex, Series
+else:
+    # we cannot unconditionally import final on python<3.8
+    final = lambda x: x
 
 
 __all__ = ["Index"]

From 9a1bb100e8925e7fd8d99542cf4d209017839ca3 Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Sat, 31 Oct 2020 09:01:06 -0700
Subject: [PATCH 7/8] put final in pd._typing

---
 pandas/_typing.py           | 6 ++++++
 pandas/core/indexes/base.py | 6 +-----
 2 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/pandas/_typing.py b/pandas/_typing.py
index a9177106535fc..2c6b7634cb7f6 100644
--- a/pandas/_typing.py
+++ b/pandas/_typing.py
@@ -27,6 +27,8 @@
 # and use a string literal forward reference to it in subsequent types
 # https://mypy.readthedocs.io/en/latest/common_issues.html#import-cycles
 if TYPE_CHECKING:
+    from typing import final
+
     from pandas._libs import Period, Timedelta, Timestamp
 
     from pandas.core.dtypes.dtypes import ExtensionDtype
@@ -39,6 +41,10 @@
     from pandas.core.series import Series
 
     from pandas.io.formats.format import EngFormatter
+else:
+    # typing.final does not exist until py38
+    final = lambda x: x
+
 
 # array-like
 
diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 1b190b18eac84..7f87513d17e09 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -17,6 +17,7 @@
     TypeVar,
     Union,
     cast,
+    final,
 )
 import warnings
 
@@ -100,12 +101,7 @@
 )
 
 if TYPE_CHECKING:
-    from typing import final
-
     from pandas import MultiIndex, RangeIndex, Series
-else:
-    # we cannot unconditionally import final on python<3.8
-    final = lambda x: x
 
 
 __all__ = ["Index"]

From 1c4b0e71db37134b0b5fc2865d983473d41cc724 Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Sat, 31 Oct 2020 11:06:09 -0700
Subject: [PATCH 8/8] fixup wrong import

---
 pandas/core/indexes/base.py | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 748ca92ac3238..91d27a4406b86 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -17,7 +17,6 @@
     TypeVar,
     Union,
     cast,
-    final,
 )
 import warnings
 
@@ -28,7 +27,7 @@
 from pandas._libs.lib import is_datetime_array, no_default
 from pandas._libs.tslibs import IncompatibleFrequency, OutOfBoundsDatetime, Timestamp
 from pandas._libs.tslibs.timezones import tz_compare
-from pandas._typing import AnyArrayLike, Dtype, DtypeObj, Label
+from pandas._typing import AnyArrayLike, Dtype, DtypeObj, Label, final
 from pandas.compat.numpy import function as nv
 from pandas.errors import DuplicateLabelError, InvalidIndexError
 from pandas.util._decorators import Appender, cache_readonly, doc