From 3e0e59ccf6cadb5ea2344ff89b944524aea7b04a Mon Sep 17 00:00:00 2001
From: Simon Hawkins <simonjayhawkins@gmail.com>
Date: Mon, 31 Aug 2020 12:49:25 +0100
Subject: [PATCH 1/2] TYP: misc typing cleanup in core/indexes/multi.py

---
 pandas/core/indexes/multi.py | 46 +++++++++++++++++++++++++-----------
 1 file changed, 32 insertions(+), 14 deletions(-)

diff --git a/pandas/core/indexes/multi.py b/pandas/core/indexes/multi.py
index b29c27982f087..546e187eb6484 100644
--- a/pandas/core/indexes/multi.py
+++ b/pandas/core/indexes/multi.py
@@ -19,7 +19,7 @@
 
 from pandas._libs import algos as libalgos, index as libindex, lib
 from pandas._libs.hashtable import duplicated_int64
-from pandas._typing import AnyArrayLike, Scalar
+from pandas._typing import AnyArrayLike, Label, Scalar
 from pandas.compat.numpy import function as nv
 from pandas.errors import InvalidIndexError, PerformanceWarning, UnsortedIndexError
 from pandas.util._decorators import Appender, cache_readonly, doc
@@ -449,7 +449,12 @@ def from_arrays(cls, arrays, sortorder=None, names=lib.no_default) -> "MultiInde
         )
 
     @classmethod
-    def from_tuples(cls, tuples, sortorder=None, names=None):
+    def from_tuples(
+        cls,
+        tuples,
+        sortorder: Optional[int] = None,
+        names: Optional[Sequence[Label]] = None,
+    ):
         """
         Convert list of tuples to MultiIndex.
 
@@ -490,6 +495,7 @@ def from_tuples(cls, tuples, sortorder=None, names=None):
         elif is_iterator(tuples):
             tuples = list(tuples)
 
+        arrays: List[Sequence[Label]]
         if len(tuples) == 0:
             if names is None:
                 raise TypeError("Cannot infer number of levels from empty list")
@@ -700,8 +706,13 @@ def levels(self):
         return FrozenList(result)
 
     def _set_levels(
-        self, levels, level=None, copy=False, validate=True, verify_integrity=False
-    ):
+        self,
+        levels,
+        level=None,
+        copy: bool = False,
+        validate: bool = True,
+        verify_integrity: bool = False,
+    ) -> None:
         # This is NOT part of the levels property because it should be
         # externally not allowed to set levels. User beware if you change
         # _levels directly
@@ -719,10 +730,10 @@ def _set_levels(
             )
         else:
             level_numbers = [self._get_level_number(lev) for lev in level]
-            new_levels = list(self._levels)
+            new_levels_list = list(self._levels)
             for lev_num, lev in zip(level_numbers, levels):
-                new_levels[lev_num] = ensure_index(lev, copy=copy)._shallow_copy()
-            new_levels = FrozenList(new_levels)
+                new_levels_list[lev_num] = ensure_index(lev, copy=copy)._shallow_copy()
+            new_levels = FrozenList(new_levels_list)
 
         if verify_integrity:
             new_codes = self._verify_integrity(levels=new_levels)
@@ -875,8 +886,13 @@ def codes(self):
         return self._codes
 
     def _set_codes(
-        self, codes, level=None, copy=False, validate=True, verify_integrity=False
-    ):
+        self,
+        codes,
+        level=None,
+        copy: bool = False,
+        validate: bool = True,
+        verify_integrity: bool = False,
+    ) -> None:
         if validate:
             if level is None and len(codes) != self.nlevels:
                 raise ValueError("Length of codes must match number of levels")
@@ -890,11 +906,13 @@ def _set_codes(
             )
         else:
             level_numbers = [self._get_level_number(lev) for lev in level]
-            new_codes = list(self._codes)
+            new_codes_list = list(self._codes)
             for lev_num, level_codes in zip(level_numbers, codes):
                 lev = self.levels[lev_num]
-                new_codes[lev_num] = _coerce_indexer_frozen(level_codes, lev, copy=copy)
-            new_codes = FrozenList(new_codes)
+                new_codes_list[lev_num] = _coerce_indexer_frozen(
+                    level_codes, lev, copy=copy
+                )
+            new_codes = FrozenList(new_codes_list)
 
         if verify_integrity:
             new_codes = self._verify_integrity(codes=new_codes)
@@ -2435,7 +2453,7 @@ def _get_partial_string_timestamp_match_key(self, key):
         if isinstance(key, str) and self.levels[0]._supports_partial_string_indexing:
             # Convert key '2016-01-01' to
             # ('2016-01-01'[, slice(None, None, None)]+)
-            key = tuple([key] + [slice(None)] * (len(self.levels) - 1))
+            key = tuple((key, *([slice(None)] * (len(self.levels) - 1))))
 
         if isinstance(key, tuple):
             # Convert (..., '2016-01-01', ...) in tuple to
@@ -3086,7 +3104,7 @@ def _update_indexer(idxr, indexer=indexer):
             elif is_list_like(k):
                 # a collection of labels to include from this level (these
                 # are or'd)
-                indexers = None
+                indexers: Optional[Int64Index] = None
                 for x in k:
                     try:
                         idxrs = _convert_to_indexer(

From 25e3582599a12cd24dc2751bd552d9ba672a2644 Mon Sep 17 00:00:00 2001
From: Simon Hawkins <simonjayhawkins@gmail.com>
Date: Tue, 1 Sep 2020 10:14:46 +0100
Subject: [PATCH 2/2] update per comments

---
 pandas/core/indexes/multi.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/pandas/core/indexes/multi.py b/pandas/core/indexes/multi.py
index 546e187eb6484..f66b009e6d505 100644
--- a/pandas/core/indexes/multi.py
+++ b/pandas/core/indexes/multi.py
@@ -2453,7 +2453,7 @@ def _get_partial_string_timestamp_match_key(self, key):
         if isinstance(key, str) and self.levels[0]._supports_partial_string_indexing:
             # Convert key '2016-01-01' to
             # ('2016-01-01'[, slice(None, None, None)]+)
-            key = tuple((key, *([slice(None)] * (len(self.levels) - 1))))
+            key = (key,) + (slice(None),) * (len(self.levels) - 1)
 
         if isinstance(key, tuple):
             # Convert (..., '2016-01-01', ...) in tuple to