From aa19aa4cb8667fe77a83e58f0cf1ae7393cfd362 Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Wed, 20 Mar 2019 09:18:09 -0500
Subject: [PATCH 01/15] #25790 Updated type hints to Python3 style in files
 outside core/arrays/

---
 pandas/core/base.py                 |  6 ++----
 pandas/core/common.py               |  3 +--
 pandas/core/dtypes/base.py          | 17 ++++++-----------
 pandas/core/frame.py                | 14 ++++++++------
 pandas/core/groupby/groupby.py      | 14 ++++++--------
 pandas/core/indexes/base.py         |  3 +--
 pandas/core/indexes/datetimelike.py |  5 ++---
 pandas/core/indexes/period.py       |  2 +-
 pandas/core/internals/blocks.py     | 12 +++++++-----
 pandas/core/internals/managers.py   |  4 ++--
 10 files changed, 36 insertions(+), 44 deletions(-)

diff --git a/pandas/core/base.py b/pandas/core/base.py
index ce91c232bb92d..9951e9eacb1c6 100644
--- a/pandas/core/base.py
+++ b/pandas/core/base.py
@@ -786,8 +786,7 @@ def base(self):
         return self.values.base
 
     @property
-    def array(self):
-        # type: () -> ExtensionArray
+    def array(self) -> ExtensionArray:
         """
         The ExtensionArray of the data backing this Series or Index.
 
@@ -962,8 +961,7 @@ def to_numpy(self, dtype=None, copy=False):
         return result
 
     @property
-    def _ndarray_values(self):
-        # type: () -> np.ndarray
+    def _ndarray_values(self) -> np.ndarray:
         """
         The data as an ndarray, possibly losing information.
 
diff --git a/pandas/core/common.py b/pandas/core/common.py
index 77b7b94e7a1f7..43c9aea0e0a0e 100644
--- a/pandas/core/common.py
+++ b/pandas/core/common.py
@@ -93,8 +93,7 @@ def maybe_box_datetimelike(value):
 values_from_object = lib.values_from_object
 
 
-def is_bool_indexer(key):
-    # type: (Any) -> bool
+def is_bool_indexer(key: Any) -> bool:
     """
     Check whether `key` is a valid boolean indexer.
 
diff --git a/pandas/core/dtypes/base.py b/pandas/core/dtypes/base.py
index 8269f8c88ffd3..7b06e20420a98 100644
--- a/pandas/core/dtypes/base.py
+++ b/pandas/core/dtypes/base.py
@@ -1,5 +1,5 @@
 """Extend pandas with custom array types"""
-from typing import List, Optional, Type
+from typing import List, Optional
 
 import numpy as np
 
@@ -65,8 +65,7 @@ def __ne__(self, other):
         return not self.__eq__(other)
 
     @property
-    def names(self):
-        # type: () -> Optional[List[str]]
+    def names(self) -> Optional[List[str]]:
         """Ordered list of field names, or None if there are no fields.
 
         This is for compatibility with NumPy arrays, and may be removed in the
@@ -116,8 +115,7 @@ def is_dtype(cls, dtype):
             return False
 
     @property
-    def _is_numeric(self):
-        # type: () -> bool
+    def _is_numeric(self) -> bool:
         """
         Whether columns with this dtype should be considered numeric.
 
@@ -128,8 +126,7 @@ def _is_numeric(self):
         return False
 
     @property
-    def _is_boolean(self):
-        # type: () -> bool
+    def _is_boolean(self) -> bool:
         """
         Whether this dtype should be considered boolean.
 
@@ -212,8 +209,7 @@ def __str__(self):
         return self.name
 
     @property
-    def type(self):
-        # type: () -> Type
+    def type(self) -> bool:
         """
         The scalar type for the array, e.g. ``int``
 
@@ -242,8 +238,7 @@ def kind(self):
         return 'O'
 
     @property
-    def name(self):
-        # type: () -> str
+    def name(self) -> str:
         """
         A string identifying the data type.
 
diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index 75f2ac8cbb7e7..61b0a2651188e 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -19,7 +19,7 @@
 import sys
 import warnings
 from textwrap import dedent
-from typing import List, Union
+from typing import List, TypeVar, Union
 
 import numpy as np
 import numpy.ma as ma
@@ -284,6 +284,10 @@
     Index(['value'], dtype='object')
 """
 
+
+DF = TypeVar('DF', bound='DataFrame')
+
+
 # -----------------------------------------------------------------------
 # DataFrame class
 
@@ -6243,11 +6247,9 @@ def diff(self, periods=1, axis=0):
     # Function application
 
     def _gotitem(self,
-                 key,           # type: Union[str, List[str]]
-                 ndim,          # type: int
-                 subset=None    # type: Union[Series, DataFrame, None]
-                 ):
-        # type: (...) -> Union[Series, DataFrame]
+                 key: Union[str, List[str]],
+                 ndim: int,
+                 subset: Union[Series, DF, None] = None) -> Union[Series, DF]:
         """
         Sub-classes to define. Return a sliced object.
 
diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index 96eafbfae2cdb..c2fad0af19b8f 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -1040,8 +1040,7 @@ def _bool_agg(self, val_test, skipna):
         Shared func to call any / all Cython GroupBy implementations.
         """
 
-        def objs_to_bool(vals):
-            # type: (np.ndarray) -> (np.ndarray, Type)
+        def objs_to_bool(vals: np.ndarray) -> types.Tuple[np.ndarray, Type]:
             if is_object_dtype(vals):
                 vals = np.array([bool(x) for x in vals])
             else:
@@ -1049,8 +1048,7 @@ def objs_to_bool(vals):
 
             return vals.view(np.uint8), np.bool
 
-        def result_to_bool(result, inference):
-            # type: (np.ndarray, Type) -> np.ndarray
+        def result_to_bool(result: np.ndarray, inference: Type) -> np.ndarray:
             return result.astype(inference, copy=False)
 
         return self._get_cythonized_result('group_any_all', self.grouper,
@@ -1738,8 +1736,8 @@ def quantile(self, q=0.5, interpolation='linear'):
         b    3.0
         """
 
-        def pre_processor(vals):
-            # type: (np.ndarray) -> (np.ndarray, Optional[Type])
+        def pre_processor(vals: np.ndarray) -> \
+                types.Tuple[np.ndarray, Optional[Type]]:
             if is_object_dtype(vals):
                 raise TypeError("'quantile' cannot be performed against "
                                 "'object' dtypes!")
@@ -1753,8 +1751,8 @@ def pre_processor(vals):
 
             return vals, inference
 
-        def post_processor(vals, inference):
-            # type: (np.ndarray, Optional[Type]) -> np.ndarray
+        def post_processor(vals: np.ndarray, inference: Optional[Type]) -> \
+                np.ndarray:
             if inference:
                 # Check for edge case
                 if not (is_integer_dtype(inference) and
diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index f6d7d27eca598..8788ede970064 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -3632,8 +3632,7 @@ def values(self):
         return self._data.view(np.ndarray)
 
     @property
-    def _values(self):
-        # type: () -> Union[ExtensionArray, Index, np.ndarray]
+    def _values(self) -> Union[ExtensionArray, Index, np.ndarray]:
         # TODO(EA): remove index types as they become extension arrays
         """
         The best array representation.
diff --git a/pandas/core/indexes/datetimelike.py b/pandas/core/indexes/datetimelike.py
index 830f234b85757..4575081f52b71 100644
--- a/pandas/core/indexes/datetimelike.py
+++ b/pandas/core/indexes/datetimelike.py
@@ -56,7 +56,7 @@ class DatetimeIndexOpsMixin(ExtensionOpsMixin):
     """
     common ops mixin to support a unified interface datetimelike Index
     """
-    _data = None  # type: DatetimeLikeArrayMixin
+    _data: DatetimeLikeArrayMixin = None
 
     # DatetimeLikeArrayMixin assumes subclasses are mutable, so these are
     # properties there.  They can be made into cache_readonly for Index
@@ -129,8 +129,7 @@ def _ndarray_values(self):
     # Abstract data attributes
 
     @property
-    def values(self):
-        # type: () -> np.ndarray
+    def values(self) -> np.ndarray:
         # Note: PeriodArray overrides this to return an ndarray of objects.
         return self._data._data
 
diff --git a/pandas/core/indexes/period.py b/pandas/core/indexes/period.py
index a4bd7f9017eb4..ae18f63fe3ba4 100644
--- a/pandas/core/indexes/period.py
+++ b/pandas/core/indexes/period.py
@@ -170,7 +170,7 @@ class PeriodIndex(DatetimeIndexOpsMixin, Int64Index, PeriodDelegateMixin):
     _is_numeric_dtype = False
     _infer_as_myclass = True
 
-    _data = None  # type: PeriodArray
+    _data: PeriodArray = None
 
     _engine_type = libindex.PeriodEngine
 
diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index a61bc30a126e6..c79cf90a9c447 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -3,7 +3,7 @@
 import functools
 import inspect
 import re
-from typing import Any, List
+from typing import Any, List, Optional, TypeVar
 import warnings
 
 import numpy as np
@@ -1646,6 +1646,9 @@ def _get_unstack_items(self, unstacker, new_columns):
         return new_placement, new_values, mask
 
 
+EB = TypeVar('EB', bound='ExtensionBlock')
+
+
 class ExtensionBlock(NonConsolidatableMixIn, Block):
     """Block for holding extension types.
 
@@ -1828,10 +1831,9 @@ def interpolate(self, method='pad', axis=0, inplace=False, limit=None,
             placement=self.mgr_locs)
 
     def shift(self,
-              periods,                  # type: int
-              axis=0,                   # type: libinternals.BlockPlacement
-              fill_value=None):         # type: Any
-        # type: (...) -> List[ExtensionBlock]
+              periods: int,
+              axis: libinternals.BlockPlacement = 0,
+              fill_value: Optional[Any] = None) -> List[EB]:
         """
         Shift the block by `periods`.
 
diff --git a/pandas/core/internals/managers.py b/pandas/core/internals/managers.py
index b9d478f3f14eb..06dd0596a6183 100644
--- a/pandas/core/internals/managers.py
+++ b/pandas/core/internals/managers.py
@@ -1863,8 +1863,8 @@ def _shape_compat(x):
     return stacked, placement
 
 
-def _interleaved_dtype(blocks):
-    # type: (List[Block]) -> Optional[Union[np.dtype, ExtensionDtype]]
+def _interleaved_dtype(blocks: List[Block]) \
+        -> Optional[Union[np.dtype, ExtensionDtype]]:
     """Find the common dtype for `blocks`.
 
     Parameters

From 014c48e9e239deb6cc97d72c42f44cd109c950f9 Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Wed, 20 Mar 2019 09:22:19 -0500
Subject: [PATCH 02/15] #25790 Added TypeVar to hint in core/indexes/base.py

---
 pandas/core/indexes/base.py | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 8788ede970064..504baff8f379f 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -1,7 +1,7 @@
 from datetime import datetime, timedelta
 import operator
 from textwrap import dedent
-from typing import Union
+from typing import TypeVar, Union
 import warnings
 
 import numpy as np
@@ -164,6 +164,9 @@ def _new_Index(cls, d):
     return cls.__new__(cls, **d)
 
 
+INDEXTYPE = TypeVar('INDEXTYPE', bound='Index')
+
+
 class Index(IndexOpsMixin, PandasObject):
     """
     Immutable ndarray implementing an ordered, sliceable set. The basic object
@@ -3632,7 +3635,7 @@ def values(self):
         return self._data.view(np.ndarray)
 
     @property
-    def _values(self) -> Union[ExtensionArray, Index, np.ndarray]:
+    def _values(self) -> Union[ExtensionArray, INDEXTYPE, np.ndarray]:
         # TODO(EA): remove index types as they become extension arrays
         """
         The best array representation.

From 5e991b6794fd85c5a56c1afed128a0e2c1bcdc86 Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Wed, 20 Mar 2019 10:12:15 -0500
Subject: [PATCH 03/15] Fixed reference to types.Tuple that should have been to
 typing.Tuple

---
 pandas/core/groupby/groupby.py | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index c2fad0af19b8f..25bbdd81d0a89 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -12,7 +12,7 @@ class providing the base-class of operations.
 import datetime
 from functools import partial, wraps
 import types
-from typing import Optional, Type
+from typing import Optional, Type, Tuple
 import warnings
 
 import numpy as np
@@ -1040,7 +1040,7 @@ def _bool_agg(self, val_test, skipna):
         Shared func to call any / all Cython GroupBy implementations.
         """
 
-        def objs_to_bool(vals: np.ndarray) -> types.Tuple[np.ndarray, Type]:
+        def objs_to_bool(vals: np.ndarray) -> Tuple[np.ndarray, Type]:
             if is_object_dtype(vals):
                 vals = np.array([bool(x) for x in vals])
             else:
@@ -1737,7 +1737,7 @@ def quantile(self, q=0.5, interpolation='linear'):
         """
 
         def pre_processor(vals: np.ndarray) -> \
-                types.Tuple[np.ndarray, Optional[Type]]:
+                Tuple[np.ndarray, Optional[Type]]:
             if is_object_dtype(vals):
                 raise TypeError("'quantile' cannot be performed against "
                                 "'object' dtypes!")

From 0efb21d22aef259972ed7718d32a3a28ec29c2b8 Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Wed, 20 Mar 2019 10:43:12 -0500
Subject: [PATCH 04/15] Fixed import sort

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

diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index 25bbdd81d0a89..c5a1a78093b2b 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -12,7 +12,7 @@ class providing the base-class of operations.
 import datetime
 from functools import partial, wraps
 import types
-from typing import Optional, Type, Tuple
+from typing import Optional, Tuple, Type
 import warnings
 
 import numpy as np

From d2a542bd6bafd1be9e29c347bc0a90cc9aec449e Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Wed, 20 Mar 2019 12:35:41 -0500
Subject: [PATCH 05/15] Replaced TypeVars with forward references

---
 pandas/core/frame.py            | 8 +++-----
 pandas/core/indexes/base.py     | 7 ++-----
 pandas/core/internals/blocks.py | 7 ++-----
 3 files changed, 7 insertions(+), 15 deletions(-)

diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index 61b0a2651188e..f9afe19b12d62 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -19,7 +19,7 @@
 import sys
 import warnings
 from textwrap import dedent
-from typing import List, TypeVar, Union
+from typing import List, Union
 
 import numpy as np
 import numpy.ma as ma
@@ -285,9 +285,6 @@
 """
 
 
-DF = TypeVar('DF', bound='DataFrame')
-
-
 # -----------------------------------------------------------------------
 # DataFrame class
 
@@ -6249,7 +6246,8 @@ def diff(self, periods=1, axis=0):
     def _gotitem(self,
                  key: Union[str, List[str]],
                  ndim: int,
-                 subset: Union[Series, DF, None] = None) -> Union[Series, DF]:
+                 subset: Union[Series, 'DataFrame', None] = None,
+                 ) -> Union[Series, 'DataFrame']:
         """
         Sub-classes to define. Return a sliced object.
 
diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 504baff8f379f..813127968581c 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -1,7 +1,7 @@
 from datetime import datetime, timedelta
 import operator
 from textwrap import dedent
-from typing import TypeVar, Union
+from typing import Union
 import warnings
 
 import numpy as np
@@ -164,9 +164,6 @@ def _new_Index(cls, d):
     return cls.__new__(cls, **d)
 
 
-INDEXTYPE = TypeVar('INDEXTYPE', bound='Index')
-
-
 class Index(IndexOpsMixin, PandasObject):
     """
     Immutable ndarray implementing an ordered, sliceable set. The basic object
@@ -3635,7 +3632,7 @@ def values(self):
         return self._data.view(np.ndarray)
 
     @property
-    def _values(self) -> Union[ExtensionArray, INDEXTYPE, np.ndarray]:
+    def _values(self) -> Union[ExtensionArray, 'Index', np.ndarray]:
         # TODO(EA): remove index types as they become extension arrays
         """
         The best array representation.
diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index c79cf90a9c447..ddc47b04cc79e 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -3,7 +3,7 @@
 import functools
 import inspect
 import re
-from typing import Any, List, Optional, TypeVar
+from typing import Any, List, Optional
 import warnings
 
 import numpy as np
@@ -1646,9 +1646,6 @@ def _get_unstack_items(self, unstacker, new_columns):
         return new_placement, new_values, mask
 
 
-EB = TypeVar('EB', bound='ExtensionBlock')
-
-
 class ExtensionBlock(NonConsolidatableMixIn, Block):
     """Block for holding extension types.
 
@@ -1833,7 +1830,7 @@ def interpolate(self, method='pad', axis=0, inplace=False, limit=None,
     def shift(self,
               periods: int,
               axis: libinternals.BlockPlacement = 0,
-              fill_value: Optional[Any] = None) -> List[EB]:
+              fill_value: Optional[Any] = None) -> List['ExtensionBlock']:
         """
         Shift the block by `periods`.
 

From 1341a1e2e0c56f84c778989ce25c6cad62b08e9c Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Wed, 20 Mar 2019 15:45:05 -0500
Subject: [PATCH 06/15] Made changes requested by @WillAyd

---
 pandas/core/groupby/groupby.py    |  6 ++++--
 pandas/core/internals/blocks.py   | 12 +++++++-----
 pandas/core/internals/managers.py |  5 +++--
 3 files changed, 14 insertions(+), 9 deletions(-)

diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index c5a1a78093b2b..a5eff2644491d 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -1751,8 +1751,10 @@ def pre_processor(vals: np.ndarray) -> \
 
             return vals, inference
 
-        def post_processor(vals: np.ndarray, inference: Optional[Type]) -> \
-                np.ndarray:
+        def post_processor(
+                vals: np.ndarray,
+                inference: Optional[Type]
+        ) -> np.ndarray:
             if inference:
                 # Check for edge case
                 if not (is_integer_dtype(inference) and
diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index ddc47b04cc79e..243cd03980a70 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -3,7 +3,7 @@
 import functools
 import inspect
 import re
-from typing import Any, List, Optional
+from typing import Any, List
 import warnings
 
 import numpy as np
@@ -1827,10 +1827,12 @@ def interpolate(self, method='pad', axis=0, inplace=False, limit=None,
                                  limit=limit),
             placement=self.mgr_locs)
 
-    def shift(self,
-              periods: int,
-              axis: libinternals.BlockPlacement = 0,
-              fill_value: Optional[Any] = None) -> List['ExtensionBlock']:
+    def shift(
+            self,
+            periods: int,
+            axis: libinternals.BlockPlacement = 0,
+            fill_value: Any = None
+    ) -> List['ExtensionBlock']:
         """
         Shift the block by `periods`.
 
diff --git a/pandas/core/internals/managers.py b/pandas/core/internals/managers.py
index 06dd0596a6183..e12b091f2e0e7 100644
--- a/pandas/core/internals/managers.py
+++ b/pandas/core/internals/managers.py
@@ -1863,8 +1863,9 @@ def _shape_compat(x):
     return stacked, placement
 
 
-def _interleaved_dtype(blocks: List[Block]) \
-        -> Optional[Union[np.dtype, ExtensionDtype]]:
+def _interleaved_dtype(
+        blocks: List[Block]
+) -> Optional[Union[np.dtype, ExtensionDtype]]:
     """Find the common dtype for `blocks`.
 
     Parameters

From 1e6e679b6c82a7d883ce2c061e88362f5796ef92 Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Thu, 21 Mar 2019 07:42:56 -0500
Subject: [PATCH 07/15] Removed class and instance variable type hints for 3.5
 compatibility

---
 pandas/core/indexes/datetimelike.py | 2 +-
 pandas/core/indexes/period.py       | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/pandas/core/indexes/datetimelike.py b/pandas/core/indexes/datetimelike.py
index 4575081f52b71..3fa7acfff6092 100644
--- a/pandas/core/indexes/datetimelike.py
+++ b/pandas/core/indexes/datetimelike.py
@@ -56,7 +56,7 @@ class DatetimeIndexOpsMixin(ExtensionOpsMixin):
     """
     common ops mixin to support a unified interface datetimelike Index
     """
-    _data: DatetimeLikeArrayMixin = None
+    _data = None  # type: DatetimeLikeArrayMixin
 
     # DatetimeLikeArrayMixin assumes subclasses are mutable, so these are
     # properties there.  They can be made into cache_readonly for Index
diff --git a/pandas/core/indexes/period.py b/pandas/core/indexes/period.py
index ae18f63fe3ba4..a4bd7f9017eb4 100644
--- a/pandas/core/indexes/period.py
+++ b/pandas/core/indexes/period.py
@@ -170,7 +170,7 @@ class PeriodIndex(DatetimeIndexOpsMixin, Int64Index, PeriodDelegateMixin):
     _is_numeric_dtype = False
     _infer_as_myclass = True
 
-    _data: PeriodArray = None
+    _data = None  # type: PeriodArray
 
     _engine_type = libindex.PeriodEngine
 

From 13fc9ca63034d2cf4ee6ed71d59e596d63db2758 Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Thu, 21 Mar 2019 20:46:58 -0500
Subject: [PATCH 08/15] Requested changes

---
 pandas/core/dtypes/base.py | 2 +-
 pandas/core/frame.py       | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/pandas/core/dtypes/base.py b/pandas/core/dtypes/base.py
index 7b06e20420a98..25f084dee18ba 100644
--- a/pandas/core/dtypes/base.py
+++ b/pandas/core/dtypes/base.py
@@ -209,7 +209,7 @@ def __str__(self):
         return self.name
 
     @property
-    def type(self) -> bool:
+    def type(self) -> type:
         """
         The scalar type for the array, e.g. ``int``
 
diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index f9afe19b12d62..d30920da33a04 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -19,7 +19,7 @@
 import sys
 import warnings
 from textwrap import dedent
-from typing import List, Union
+from typing import List, Optional, Union
 
 import numpy as np
 import numpy.ma as ma
@@ -6246,7 +6246,7 @@ def diff(self, periods=1, axis=0):
     def _gotitem(self,
                  key: Union[str, List[str]],
                  ndim: int,
-                 subset: Union[Series, 'DataFrame', None] = None,
+                 subset: Optional[Series, 'DataFrame'] = None,
                  ) -> Union[Series, 'DataFrame']:
         """
         Sub-classes to define. Return a sliced object.

From 3c07c5ede5020d72d466822b022ba97b47c450bf Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Thu, 21 Mar 2019 21:11:26 -0500
Subject: [PATCH 09/15] Fixed type Optional[] hint

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

diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index d30920da33a04..41db89cf5cf6c 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -6246,7 +6246,7 @@ def diff(self, periods=1, axis=0):
     def _gotitem(self,
                  key: Union[str, List[str]],
                  ndim: int,
-                 subset: Optional[Series, 'DataFrame'] = None,
+                 subset: Optional[Union[Series, 'DataFrame']] = None,
                  ) -> Union[Series, 'DataFrame']:
         """
         Sub-classes to define. Return a sliced object.

From c774e4aa556096e03f942ffeb787539ce8249c06 Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Fri, 22 Mar 2019 11:09:48 -0500
Subject: [PATCH 10/15] Updates to correct errors revealed by mypy

---
 pandas/core/dtypes/base.py     | 4 ++--
 pandas/core/frame.py           | 4 ++--
 pandas/core/groupby/groupby.py | 7 ++++---
 3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/pandas/core/dtypes/base.py b/pandas/core/dtypes/base.py
index 25f084dee18ba..3ec49a4cdf331 100644
--- a/pandas/core/dtypes/base.py
+++ b/pandas/core/dtypes/base.py
@@ -1,5 +1,5 @@
 """Extend pandas with custom array types"""
-from typing import List, Optional
+from typing import List, Optional, Type
 
 import numpy as np
 
@@ -209,7 +209,7 @@ def __str__(self):
         return self.name
 
     @property
-    def type(self) -> type:
+    def type(self) -> Type:
         """
         The scalar type for the array, e.g. ``int``
 
diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index 41db89cf5cf6c..7a8e71b8009e4 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -19,7 +19,7 @@
 import sys
 import warnings
 from textwrap import dedent
-from typing import List, Optional, Union
+from typing import List, Optional, Set, Union
 
 import numpy as np
 import numpy.ma as ma
@@ -367,7 +367,7 @@ def _constructor(self):
     _constructor_sliced = Series
     _deprecations = NDFrame._deprecations | frozenset(
         ['get_value', 'set_value', 'from_csv', 'from_items'])
-    _accessors = set()
+    _accessors = set()  # type: Set
 
     @property
     def _constructor_expanddim(self):
diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index a5eff2644491d..fb310b6e5b722 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -12,7 +12,7 @@ class providing the base-class of operations.
 import datetime
 from functools import partial, wraps
 import types
-from typing import Optional, Tuple, Type
+from typing import Optional, Tuple, Type, Union
 import warnings
 
 import numpy as np
@@ -1736,8 +1736,9 @@ def quantile(self, q=0.5, interpolation='linear'):
         b    3.0
         """
 
-        def pre_processor(vals: np.ndarray) -> \
-                Tuple[np.ndarray, Optional[Type]]:
+        def pre_processor(
+                vals: np.ndarray
+        ) -> Tuple[np.ndarray, Optional[Union[str, Type]]]:
             if is_object_dtype(vals):
                 raise TypeError("'quantile' cannot be performed against "
                                 "'object' dtypes!")

From a5fd6521f5a58d7fad0c15e6e427a061ae0877e2 Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Sat, 23 Mar 2019 22:22:05 -0500
Subject: [PATCH 11/15] Revert "Updates to correct errors revealed by mypy"

This reverts commit c774e4aa556096e03f942ffeb787539ce8249c06.
---
 pandas/core/dtypes/base.py     | 4 ++--
 pandas/core/frame.py           | 4 ++--
 pandas/core/groupby/groupby.py | 7 +++----
 3 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/pandas/core/dtypes/base.py b/pandas/core/dtypes/base.py
index 3ec49a4cdf331..25f084dee18ba 100644
--- a/pandas/core/dtypes/base.py
+++ b/pandas/core/dtypes/base.py
@@ -1,5 +1,5 @@
 """Extend pandas with custom array types"""
-from typing import List, Optional, Type
+from typing import List, Optional
 
 import numpy as np
 
@@ -209,7 +209,7 @@ def __str__(self):
         return self.name
 
     @property
-    def type(self) -> Type:
+    def type(self) -> type:
         """
         The scalar type for the array, e.g. ``int``
 
diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index 7a8e71b8009e4..41db89cf5cf6c 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -19,7 +19,7 @@
 import sys
 import warnings
 from textwrap import dedent
-from typing import List, Optional, Set, Union
+from typing import List, Optional, Union
 
 import numpy as np
 import numpy.ma as ma
@@ -367,7 +367,7 @@ def _constructor(self):
     _constructor_sliced = Series
     _deprecations = NDFrame._deprecations | frozenset(
         ['get_value', 'set_value', 'from_csv', 'from_items'])
-    _accessors = set()  # type: Set
+    _accessors = set()
 
     @property
     def _constructor_expanddim(self):
diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index fb310b6e5b722..a5eff2644491d 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -12,7 +12,7 @@ class providing the base-class of operations.
 import datetime
 from functools import partial, wraps
 import types
-from typing import Optional, Tuple, Type, Union
+from typing import Optional, Tuple, Type
 import warnings
 
 import numpy as np
@@ -1736,9 +1736,8 @@ def quantile(self, q=0.5, interpolation='linear'):
         b    3.0
         """
 
-        def pre_processor(
-                vals: np.ndarray
-        ) -> Tuple[np.ndarray, Optional[Union[str, Type]]]:
+        def pre_processor(vals: np.ndarray) -> \
+                Tuple[np.ndarray, Optional[Type]]:
             if is_object_dtype(vals):
                 raise TypeError("'quantile' cannot be performed against "
                                 "'object' dtypes!")

From dcabf976b5b8988cf8e1d03ac24bf70ebbf8e6e4 Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Sat, 23 Mar 2019 22:24:41 -0500
Subject: [PATCH 12/15] Fix line formatting

---
 pandas/core/groupby/groupby.py | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index a5eff2644491d..3c3addd06b94a 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -1736,8 +1736,9 @@ def quantile(self, q=0.5, interpolation='linear'):
         b    3.0
         """
 
-        def pre_processor(vals: np.ndarray) -> \
-                Tuple[np.ndarray, Optional[Type]]:
+        def pre_processor(
+                vals: np.ndarray
+        ) -> Tuple[np.ndarray, Optional[Type]]:
             if is_object_dtype(vals):
                 raise TypeError("'quantile' cannot be performed against "
                                 "'object' dtypes!")

From 75ba127b60f4edf3703d22dd06c188843b8184c4 Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Sun, 24 Mar 2019 21:21:29 -0500
Subject: [PATCH 13/15] Replace forward references with ABCs

---
 pandas/core/frame.py        | 7 ++++---
 pandas/core/indexes/base.py | 2 +-
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/pandas/core/frame.py b/pandas/core/frame.py
index 41db89cf5cf6c..5ccd10ac564df 100644
--- a/pandas/core/frame.py
+++ b/pandas/core/frame.py
@@ -72,7 +72,8 @@
     is_iterator,
     is_sequence,
     is_named_tuple)
-from pandas.core.dtypes.generic import ABCSeries, ABCIndexClass, ABCMultiIndex
+from pandas.core.dtypes.generic import (
+    ABCSeries, ABCDataFrame, ABCIndexClass, ABCMultiIndex)
 from pandas.core.dtypes.missing import isna, notna
 
 from pandas.core import algorithms
@@ -6246,8 +6247,8 @@ def diff(self, periods=1, axis=0):
     def _gotitem(self,
                  key: Union[str, List[str]],
                  ndim: int,
-                 subset: Optional[Union[Series, 'DataFrame']] = None,
-                 ) -> Union[Series, 'DataFrame']:
+                 subset: Optional[Union[Series, ABCDataFrame]] = None,
+                 ) -> Union[Series, ABCDataFrame]:
         """
         Sub-classes to define. Return a sliced object.
 
diff --git a/pandas/core/indexes/base.py b/pandas/core/indexes/base.py
index 813127968581c..e2e4bad6c147b 100644
--- a/pandas/core/indexes/base.py
+++ b/pandas/core/indexes/base.py
@@ -3632,7 +3632,7 @@ def values(self):
         return self._data.view(np.ndarray)
 
     @property
-    def _values(self) -> Union[ExtensionArray, 'Index', np.ndarray]:
+    def _values(self) -> Union[ExtensionArray, ABCIndexClass, np.ndarray]:
         # TODO(EA): remove index types as they become extension arrays
         """
         The best array representation.

From 70fe87e404cd4883f4834d6aafdf3d75a8f4daf6 Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Wed, 27 Mar 2019 10:09:15 -0500
Subject: [PATCH 14/15] type to Type

---
 pandas/core/dtypes/base.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pandas/core/dtypes/base.py b/pandas/core/dtypes/base.py
index 25f084dee18ba..3ec49a4cdf331 100644
--- a/pandas/core/dtypes/base.py
+++ b/pandas/core/dtypes/base.py
@@ -1,5 +1,5 @@
 """Extend pandas with custom array types"""
-from typing import List, Optional
+from typing import List, Optional, Type
 
 import numpy as np
 
@@ -209,7 +209,7 @@ def __str__(self):
         return self.name
 
     @property
-    def type(self) -> type:
+    def type(self) -> Type:
         """
         The scalar type for the array, e.g. ``int``
 

From ce92ce84672009e5d62945cd47643e89f5bba99b Mon Sep 17 00:00:00 2001
From: Gregory Rome <gwrome@gmail.com>
Date: Wed, 27 Mar 2019 16:26:45 -0500
Subject: [PATCH 15/15] Trigger tests again