From 552715a877ba13cb303db145402dd6ab3546d209 Mon Sep 17 00:00:00 2001
From: Marco Gorelli <marcogorelli@protonmail.com>
Date: Thu, 28 Jan 2021 16:59:01 +0000
Subject: [PATCH] annotate some variables, remove some unused

---
 pandas/_config/display.py              |  3 ++-
 pandas/core/computation/expressions.py | 10 ++++++----
 pandas/core/generic.py                 |  5 ++---
 pandas/core/series.py                  |  2 +-
 pandas/io/excel/_base.py               |  1 -
 pandas/io/excel/_util.py               |  4 ++--
 pandas/io/sql.py                       |  2 +-
 7 files changed, 14 insertions(+), 13 deletions(-)

diff --git a/pandas/_config/display.py b/pandas/_config/display.py
index e4553a2107f87..ec819481525da 100644
--- a/pandas/_config/display.py
+++ b/pandas/_config/display.py
@@ -4,12 +4,13 @@
 
 import locale
 import sys
+from typing import Optional
 
 from pandas._config import config as cf
 
 # -----------------------------------------------------------------------------
 # Global formatting options
-_initial_defencoding = None
+_initial_defencoding: Optional[str] = None
 
 
 def detect_console_encoding() -> str:
diff --git a/pandas/core/computation/expressions.py b/pandas/core/computation/expressions.py
index e5ede3cd885be..087b7f39e3374 100644
--- a/pandas/core/computation/expressions.py
+++ b/pandas/core/computation/expressions.py
@@ -6,13 +6,15 @@
 
 """
 import operator
-from typing import List, Set
+from typing import List, Optional, Set
 import warnings
 
 import numpy as np
 
 from pandas._config import get_option
 
+from pandas._typing import FuncType
+
 from pandas.core.dtypes.generic import ABCDataFrame
 
 from pandas.core.computation.check import NUMEXPR_INSTALLED
@@ -21,11 +23,11 @@
 if NUMEXPR_INSTALLED:
     import numexpr as ne
 
-_TEST_MODE = None
+_TEST_MODE: Optional[bool] = None
 _TEST_RESULT: List[bool] = []
 USE_NUMEXPR = NUMEXPR_INSTALLED
-_evaluate = None
-_where = None
+_evaluate: Optional[FuncType] = None
+_where: Optional[FuncType] = None
 
 # the set of dtypes that we will allow pass to numexpr
 _ALLOWED_DTYPES = {
diff --git a/pandas/core/generic.py b/pandas/core/generic.py
index 96b35f1aaab9c..5d668b9668e5a 100644
--- a/pandas/core/generic.py
+++ b/pandas/core/generic.py
@@ -180,7 +180,7 @@ class NDFrame(PandasObject, SelectionMixin, indexing.IndexingMixin):
         ["_AXIS_NAMES", "_AXIS_NUMBERS", "get_values", "tshift"]
     )
     _metadata: List[str] = []
-    _is_copy = None
+    _is_copy: Optional[weakref.ReferenceType[NDFrame]] = None
     _mgr: Manager
     _attrs: Dict[Optional[Hashable], Any]
     _typ: str
@@ -405,7 +405,6 @@ def _data(self):
     # Axis
     _stat_axis_number = 0
     _stat_axis_name = "index"
-    _ix = None
     _AXIS_ORDERS: List[str]
     _AXIS_TO_AXIS_NUMBER: Dict[Axis, int] = {0: 0, "index": 0, "rows": 0}
     _AXIS_REVERSED: bool
@@ -3831,7 +3830,7 @@ def _slice(self: FrameOrSeries, slobj: slice, axis=0) -> FrameOrSeries:
         return result
 
     @final
-    def _set_is_copy(self, ref, copy: bool_t = True) -> None:
+    def _set_is_copy(self, ref: FrameOrSeries, copy: bool_t = True) -> None:
         if not copy:
             self._is_copy = None
         else:
diff --git a/pandas/core/series.py b/pandas/core/series.py
index f75292f32dbca..81db9a29c514d 100644
--- a/pandas/core/series.py
+++ b/pandas/core/series.py
@@ -412,7 +412,7 @@ def _constructor_expanddim(self) -> Type[DataFrame]:
     def _can_hold_na(self) -> bool:
         return self._mgr._can_hold_na
 
-    _index = None
+    _index: Optional[Index] = None
 
     def _set_axis(self, axis: int, labels, fastpath: bool = False) -> None:
         """
diff --git a/pandas/io/excel/_base.py b/pandas/io/excel/_base.py
index 11974d25d72d3..085df983c3669 100644
--- a/pandas/io/excel/_base.py
+++ b/pandas/io/excel/_base.py
@@ -747,7 +747,6 @@ def __new__(cls, path, engine=None, **kwargs):
         return object.__new__(cls)
 
     # declare external properties you can count on
-    curr_sheet = None
     path = None
 
     @property
diff --git a/pandas/io/excel/_util.py b/pandas/io/excel/_util.py
index ab8e0fca4bf38..01ccc9d15a6a3 100644
--- a/pandas/io/excel/_util.py
+++ b/pandas/io/excel/_util.py
@@ -1,10 +1,10 @@
-from typing import List
+from typing import List, MutableMapping
 
 from pandas.compat._optional import import_optional_dependency
 
 from pandas.core.dtypes.common import is_integer, is_list_like
 
-_writers = {}
+_writers: MutableMapping[str, str] = {}
 
 
 def register_writer(klass):
diff --git a/pandas/io/sql.py b/pandas/io/sql.py
index e1af3169420fc..725cb633918e7 100644
--- a/pandas/io/sql.py
+++ b/pandas/io/sql.py
@@ -35,7 +35,7 @@ class DatabaseError(IOError):
 # -----------------------------------------------------------------------------
 # -- Helper functions
 
-_SQLALCHEMY_INSTALLED = None
+_SQLALCHEMY_INSTALLED: Optional[bool] = None
 
 
 def _is_sqlalchemy_connectable(con):