From 1043a205d197739500d6c75a9dbc40abf713837e Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Mon, 15 Jul 2019 18:36:16 -0700
Subject: [PATCH 01/16] stop conflating iNaT with td64-NaT

---
 pandas/core/internals/blocks.py     | 21 +++++++--------------
 pandas/core/nanops.py               |  8 ++++++++
 pandas/tests/series/test_missing.py |  7 +++++--
 3 files changed, 20 insertions(+), 16 deletions(-)

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 897a82f9a1968..c0d3368c652ec 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -2597,6 +2597,7 @@ class TimeDeltaBlock(DatetimeLikeBlockMixin, IntBlock):
     is_timedelta = True
     _can_hold_na = True
     is_numeric = False
+    fill_value = np.timedelta64("NaT", "ns")
 
     def __init__(self, values, placement, ndim=None):
         if values.dtype != _TD_DTYPE:
@@ -2617,15 +2618,11 @@ def _box_func(self):
     def _can_hold_element(self, element):
         tipo = maybe_infer_dtype_type(element)
         if tipo is not None:
-            # TODO: remove the np.int64 support once coerce_values and
-            #  _try_coerce_args both coerce to m8[ns] and not i8.
-            return issubclass(tipo.type, (np.timedelta64, np.int64))
+            return issubclass(tipo.type, np.timedelta64)
         elif element is NaT:
             return True
         elif isinstance(element, (timedelta, np.timedelta64)):
             return True
-        elif is_integer(element):
-            return element == tslibs.iNaT
         return is_valid_nat_for_dtype(element, self.dtype)
 
     def fillna(self, value, **kwargs):
@@ -2645,9 +2642,6 @@ def fillna(self, value, **kwargs):
             value = Timedelta(value, unit="s")
         return super().fillna(value, **kwargs)
 
-    def _coerce_values(self, values):
-        return values.view("i8")
-
     def _try_coerce_args(self, other):
         """
         Coerce values and other to int64, with null values converted to
@@ -2663,13 +2657,12 @@ def _try_coerce_args(self, other):
         """
 
         if is_valid_nat_for_dtype(other, self.dtype):
-            other = tslibs.iNaT
-        elif is_integer(other) and other == tslibs.iNaT:
-            pass
+            other = np.timedelta64("NaT", "ns")
         elif isinstance(other, (timedelta, np.timedelta64)):
-            other = Timedelta(other).value
+            other = Timedelta(other).to_timedelta64()
         elif hasattr(other, "dtype") and is_timedelta64_dtype(other):
-            other = other.astype("i8", copy=False).view("i8")
+            # TODO: can we get here with non-nano dtype?
+            pass
         else:
             # coercion issues
             # let higher levels handle
@@ -2683,7 +2676,7 @@ def _try_coerce_result(self, result):
             mask = isna(result)
             if result.dtype.kind in ["i", "f"]:
                 result = result.astype("m8[ns]")
-            result[mask] = tslibs.iNaT
+            result[mask] = np.timedelta64("NaT", "ns")
 
         elif isinstance(result, (np.integer, np.float)):
             result = self._box_func(result)
diff --git a/pandas/core/nanops.py b/pandas/core/nanops.py
index ce14cb22a88ce..aa255d03f9db7 100644
--- a/pandas/core/nanops.py
+++ b/pandas/core/nanops.py
@@ -1362,6 +1362,14 @@ def _nanpercentile_1d(values, mask, q, na_value, interpolation):
     quantiles : scalar or array
     """
     # mask is Union[ExtensionArray, ndarray]
+    if values.dtype.kind == "m":
+        # need to cast to integer to avoid rounding errors in numpy
+        result = _nanpercentile_1d(values.view("i8"), mask, q, na_value, interpolation)
+
+        # Note: we have to do do `astype` and not view because in general we
+        #  have float result at this point, not i8
+        return result.astype(values.dtype)
+
     values = values[~mask]
 
     if len(values) == 0:
diff --git a/pandas/tests/series/test_missing.py b/pandas/tests/series/test_missing.py
index f8a44b7f5639e..adb23fc6b94ea 100644
--- a/pandas/tests/series/test_missing.py
+++ b/pandas/tests/series/test_missing.py
@@ -780,9 +780,11 @@ def test_timedelta64_nan(self):
         td1[0] = td[0]
         assert not isna(td1[0])
 
+        # GH#16674 iNaT is treated as an integer when given by the user
         td1[1] = iNaT
-        assert isna(td1[1])
-        assert td1[1].value == iNaT
+        assert not isna(td1[1])
+        assert td1.dtype == np.object_
+        assert td1[1] == iNaT
         td1[1] = td[1]
         assert not isna(td1[1])
 
@@ -792,6 +794,7 @@ def test_timedelta64_nan(self):
         td1[2] = td[2]
         assert not isna(td1[2])
 
+        # FIXME: don't leave commented-out
         # boolean setting
         # this doesn't work, not sure numpy even supports it
         # result = td[(td>np.timedelta64(timedelta(days=3))) &

From f35754c12cba5245d939bf633623571535763d49 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Tue, 16 Jul 2019 17:01:12 -0700
Subject: [PATCH 02/16] dont allow iNaT in DatetimeBlock

---
 pandas/core/internals/blocks.py          | 31 ++++++++----------------
 pandas/core/nanops.py                    | 18 ++++++++------
 pandas/tests/frame/test_indexing.py      |  7 ++++--
 pandas/tests/internals/test_internals.py |  2 +-
 4 files changed, 26 insertions(+), 32 deletions(-)

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index c0d3368c652ec..722acbcbb5b59 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -2180,7 +2180,7 @@ def _holder(self):
 
     @property
     def fill_value(self):
-        return tslibs.iNaT
+        return np.datetime64("NaT", "ns")
 
     def get_values(self, dtype=None):
         """
@@ -2257,14 +2257,9 @@ def _can_hold_element(self, element):
             if self.is_datetimetz:
                 return tz_compare(element.tzinfo, self.dtype.tz)
             return element.tzinfo is None
-        elif is_integer(element):
-            return element == tslibs.iNaT
 
         return is_valid_nat_for_dtype(element, self.dtype)
 
-    def _coerce_values(self, values):
-        return values.view("i8")
-
     def _try_coerce_args(self, other):
         """
         Coerce other to dtype 'i8'. NaN and NaT convert to
@@ -2281,16 +2276,15 @@ def _try_coerce_args(self, other):
         base-type other
         """
         if is_valid_nat_for_dtype(other, self.dtype):
-            other = tslibs.iNaT
-        elif is_integer(other) and other == tslibs.iNaT:
-            pass
+            other = np.datetime64("NaT", "ns")
         elif isinstance(other, (datetime, np.datetime64, date)):
             other = self._box_func(other)
             if getattr(other, "tz") is not None:
                 raise TypeError("cannot coerce a Timestamp with a tz on a naive Block")
-            other = other.asm8.view("i8")
+            other = other.asm8
         elif hasattr(other, "dtype") and is_datetime64_dtype(other):
-            other = other.astype("i8", copy=False).view("i8")
+            # TODO: can we get here with non-nano?
+            pass
         else:
             # coercion issues
             # let higher levels handle
@@ -2449,8 +2443,7 @@ def _slice(self, slicer):
         return self.values[slicer]
 
     def _coerce_values(self, values):
-        # asi8 is a view, needs copy
-        return _block_shape(values.view("i8"), ndim=self.ndim)
+        return _block_shape(values, ndim=self.ndim)
 
     def _try_coerce_args(self, other):
         """
@@ -2475,21 +2468,17 @@ def _try_coerce_args(self, other):
             other = self._holder(other, dtype=self.dtype)
 
         elif is_valid_nat_for_dtype(other, self.dtype):
-            other = tslibs.iNaT
-        elif is_integer(other) and other == tslibs.iNaT:
-            pass
+            other = np.datetime64("NaT", "ns")
         elif isinstance(other, self._holder):
-            if other.tz != self.values.tz:
+            if not tz_compare(other.tz, self.values.tz):
                 raise ValueError("incompatible or non tz-aware value")
-            other = _block_shape(other.asi8, ndim=self.ndim)
+
         elif isinstance(other, (np.datetime64, datetime, date)):
             other = tslibs.Timestamp(other)
-            tz = getattr(other, "tz", None)
 
             # test we can have an equal time zone
-            if tz is None or str(tz) != str(self.values.tz):
+            if not tz_compare(other.tz, self.values.tz):
                 raise ValueError("incompatible or non tz-aware value")
-            other = other.value
         else:
             raise TypeError(other)
 
diff --git a/pandas/core/nanops.py b/pandas/core/nanops.py
index aa255d03f9db7..507bfa2345e04 100644
--- a/pandas/core/nanops.py
+++ b/pandas/core/nanops.py
@@ -1362,14 +1362,6 @@ def _nanpercentile_1d(values, mask, q, na_value, interpolation):
     quantiles : scalar or array
     """
     # mask is Union[ExtensionArray, ndarray]
-    if values.dtype.kind == "m":
-        # need to cast to integer to avoid rounding errors in numpy
-        result = _nanpercentile_1d(values.view("i8"), mask, q, na_value, interpolation)
-
-        # Note: we have to do do `astype` and not view because in general we
-        #  have float result at this point, not i8
-        return result.astype(values.dtype)
-
     values = values[~mask]
 
     if len(values) == 0:
@@ -1401,6 +1393,16 @@ def nanpercentile(values, q, axis, na_value, mask, ndim, interpolation):
     -------
     quantiles : scalar or array
     """
+    if values.dtype.kind in ["m", "M"]:
+        # need to cast to integer to avoid rounding errors in numpy
+        result = nanpercentile(
+            values.view("i8"), q, axis, na_value.view("i8"), mask, ndim, interpolation
+        )
+
+        # Note: we have to do do `astype` and not view because in general we
+        #  have float result at this point, not i8
+        return result.astype(values.dtype)
+
     if not lib.is_scalar(mask) and mask.any():
         if ndim == 1:
             return _nanpercentile_1d(
diff --git a/pandas/tests/frame/test_indexing.py b/pandas/tests/frame/test_indexing.py
index 0cb7db0e47123..756a6159fc7c5 100644
--- a/pandas/tests/frame/test_indexing.py
+++ b/pandas/tests/frame/test_indexing.py
@@ -1150,6 +1150,7 @@ def test_fancy_index_int_labels_exceptions(self, float_frame):
             with pytest.raises(KeyError, match=msg):
                 float_frame.ix[:, ["E"]] = 1
 
+            # FIXME: don't leave commented-out
             # partial setting now allows this GH2578
             # pytest.raises(KeyError, float_frame.ix.__setitem__,
             #               (slice(None, None), 'E'), 1)
@@ -1676,9 +1677,11 @@ def test_setitem_single_column_mixed_datetime(self):
         )
         assert_series_equal(result, expected)
 
-        # set an allowable datetime64 type
+        # GH#16674 iNaT is treated as an integer when given by the user
         df.loc["b", "timestamp"] = iNaT
-        assert isna(df.loc["b", "timestamp"])
+        assert not isna(df.loc["b", "timestamp"])
+        assert df["timestamp"].dtype == np.object_
+        assert df.loc["b", "timestamp"] == iNaT
 
         # allow this syntax
         df.loc["c", "timestamp"] = np.nan
diff --git a/pandas/tests/internals/test_internals.py b/pandas/tests/internals/test_internals.py
index 655e484bc34d1..ae572ae1df8a2 100644
--- a/pandas/tests/internals/test_internals.py
+++ b/pandas/tests/internals/test_internals.py
@@ -338,7 +338,7 @@ def test_try_coerce_arg(self):
         vals = (np.datetime64("2010-10-10"), datetime(2010, 10, 10), date(2010, 10, 10))
         for val in vals:
             coerced = block._try_coerce_args(val)
-            assert np.int64 == type(coerced)
+            assert np.datetime64 == type(coerced)
             assert pd.Timestamp("2010-10-10") == pd.Timestamp(coerced)
 
 

From 0a4ed9c24d28b6d28c42f8349f1cea325083b9b3 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Tue, 16 Jul 2019 17:03:05 -0700
Subject: [PATCH 03/16] fix docstring

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

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 722acbcbb5b59..d1b6f0f44bc4b 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -2633,8 +2633,8 @@ def fillna(self, value, **kwargs):
 
     def _try_coerce_args(self, other):
         """
-        Coerce values and other to int64, with null values converted to
-        iNaT. values is always ndarray-like, other may not be
+        Coerce values and other to datetime64[ns], with null values
+        converted to datetime64("NaT", "ns").
 
         Parameters
         ----------

From 1fb34fddd3e148e52553b4a3ea3c4fc7bb3bc12e Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Tue, 16 Jul 2019 21:04:41 -0700
Subject: [PATCH 04/16] coerce less

---
 pandas/core/groupby/generic.py  | 18 +++++-----
 pandas/core/groupby/groupby.py  |  7 +++-
 pandas/core/internals/blocks.py | 60 +++++++++++----------------------
 3 files changed, 36 insertions(+), 49 deletions(-)

diff --git a/pandas/core/groupby/generic.py b/pandas/core/groupby/generic.py
index 7fd0ca94e7997..da595222331d3 100644
--- a/pandas/core/groupby/generic.py
+++ b/pandas/core/groupby/generic.py
@@ -143,8 +143,10 @@ def _cython_agg_blocks(self, how, alt=None, numeric_only=True, min_count=-1):
         new_blocks = []
         new_items = []
         deleted_items = []
+        no_result = object()
         for block in data.blocks:
-
+            # Avoid inheriting result from earlier in the loop
+            result = no_result
             locs = block.mgr_locs.as_array
             try:
                 result, _ = self.grouper.aggregate(
@@ -171,15 +173,15 @@ def _cython_agg_blocks(self, how, alt=None, numeric_only=True, min_count=-1):
                 except TypeError:
                     # we may have an exception in trying to aggregate
                     # continue and exclude the block
-                    pass
-
+                    deleted_items.append(locs)
+                    continue
             finally:
+                if result is not no_result:
+                    dtype = block.values.dtype
 
-                dtype = block.values.dtype
-
-                # see if we can cast the block back to the original dtype
-                result = block._try_coerce_and_cast_result(result, dtype=dtype)
-                newb = block.make_block(result)
+                    # see if we can cast the block back to the original dtype
+                    result = block._try_coerce_and_cast_result(result, dtype=dtype)
+                    newb = block.make_block(result)
 
             new_items.append(locs)
             new_blocks.append(newb)
diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index 9aba9723e0546..44d03a386e90a 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -34,6 +34,7 @@ class providing the base-class of operations.
     is_numeric_dtype,
     is_scalar,
 )
+from pandas.core.dtypes.generic import ABCDatetimeArray
 from pandas.core.dtypes.missing import isna, notna
 
 from pandas.api.types import is_datetime64_dtype, is_integer_dtype, is_object_dtype
@@ -803,8 +804,12 @@ def _try_cast(self, result, obj, numeric_only=False):
                 # Prior results _may_ have been generated in UTC.
                 # Ensure we localize to UTC first before converting
                 # to the target timezone
+                if isinstance(obj, ABCDatetimeArray):
+                    arr = obj
+                else:
+                    arr = obj._values
                 try:
-                    result = obj._values._from_sequence(
+                    result = arr._from_sequence(
                         result, dtype="datetime64[ns, UTC]"
                     )
                     result = result.astype(dtype)
diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index d1b6f0f44bc4b..e8675ba1d7c1b 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -719,7 +719,7 @@ def _coerce_values(self, values):
         -------
         ndarray or ExtensionArray
         """
-        return values
+        return _block_shape(values, ndim=self.ndim)
 
     def _try_coerce_args(self, other):
         """ provide coercion to our input arguments """
@@ -1527,7 +1527,7 @@ def quantile(self, qs, interpolation="linear", axis=0):
             # We need to operate on i8 values for datetimetz
             # but `Block.get_values()` returns an ndarray of objects
             # right now. We need an API for "values to do numeric-like ops on"
-            values = self.values.asi8
+            values = self.values.view("M8[ns]")
 
             # TODO: NonConsolidatableMixin shape
             # Usual shape inconsistencies for ExtensionBlocks
@@ -1898,12 +1898,6 @@ def _try_cast_result(self, result, dtype=None):
         result could also be an EA Array itself, in which case it
         is already a 1-D array
         """
-        try:
-
-            result = self._holder._from_sequence(result.ravel(), dtype=dtype)
-        except Exception:
-            pass
-
         return result
 
     def formatting_values(self):
@@ -2294,12 +2288,9 @@ def _try_coerce_args(self, other):
 
     def _try_coerce_result(self, result):
         """ reverse of try_coerce_args """
-        if isinstance(result, np.ndarray):
-            if result.dtype.kind in ["i", "f"]:
-                result = result.astype("M8[ns]")
-
-        elif isinstance(result, (np.integer, np.float, np.datetime64)):
-            result = self._box_func(result)
+        if isinstance(result, np.ndarray) and result.dtype.kind == "i":
+            # needed for _interpolate_with_ffill
+            result = result.view("M8[ns]")
         return result
 
     @property
@@ -2361,6 +2352,7 @@ class DatetimeTZBlock(ExtensionBlock, DatetimeBlock):
     is_extension = True
 
     _can_hold_element = DatetimeBlock._can_hold_element
+    fill_value = np.datetime64("NaT", "ns")
 
     @property
     def _holder(self):
@@ -2442,9 +2434,6 @@ def _slice(self, slicer):
             return self.values[loc]
         return self.values[slicer]
 
-    def _coerce_values(self, values):
-        return _block_shape(values, ndim=self.ndim)
-
     def _try_coerce_args(self, other):
         """
         localize and return i8 for the values
@@ -2487,22 +2476,22 @@ def _try_coerce_args(self, other):
     def _try_coerce_result(self, result):
         """ reverse of try_coerce_args """
         if isinstance(result, np.ndarray):
-            if result.dtype.kind in ["i", "f"]:
-                result = result.astype("M8[ns]")
+            if result.ndim == 2:
+                result = result[0, :]
+            if result.dtype == np.float64:
+                # needed for post-groupby.median
+                result = self._holder._from_sequence(
+                    result.astype(np.int64), freq=None, dtype=self.values.dtype
+                )
+            elif result.dtype == "M8[ns]":
+                # otherwise we get here via quantile and already have M8[ns]
+                result = self._holder._simple_new(
+                    result, freq=None, dtype=self.values.dtype
+                )
 
-        elif isinstance(result, (np.integer, np.float, np.datetime64)):
+        elif isinstance(result, np.datetime64):
+            # also for post-quantile
             result = self._box_func(result)
-
-        if isinstance(result, np.ndarray):
-            # allow passing of > 1dim if its trivial
-
-            if result.ndim > 1:
-                result = result.reshape(np.prod(result.shape))
-            # GH#24096 new values invalidates a frequency
-            result = self._holder._simple_new(
-                result, freq=None, dtype=self.values.dtype
-            )
-
         return result
 
     @property
@@ -2661,15 +2650,6 @@ def _try_coerce_args(self, other):
 
     def _try_coerce_result(self, result):
         """ reverse of try_coerce_args / try_operate """
-        if isinstance(result, np.ndarray):
-            mask = isna(result)
-            if result.dtype.kind in ["i", "f"]:
-                result = result.astype("m8[ns]")
-            result[mask] = np.timedelta64("NaT", "ns")
-
-        elif isinstance(result, (np.integer, np.float)):
-            result = self._box_func(result)
-
         return result
 
     def should_store(self, value):

From be2e42a09b0fd65de4755a924964d2e2e2d9b46c Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Tue, 16 Jul 2019 21:20:08 -0700
Subject: [PATCH 05/16] cleanup

---
 pandas/core/internals/blocks.py | 18 ++++--------------
 1 file changed, 4 insertions(+), 14 deletions(-)

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index e8675ba1d7c1b..7b76b81c81fe4 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -7,7 +7,7 @@
 
 import numpy as np
 
-from pandas._libs import NaT, lib, tslib, tslibs
+from pandas._libs import NaT, lib, tslib, tslibs, Timestamp
 import pandas._libs.internals as libinternals
 from pandas._libs.tslibs import Timedelta, conversion
 from pandas._libs.tslibs.timezones import tz_compare
@@ -2272,8 +2272,8 @@ def _try_coerce_args(self, other):
         if is_valid_nat_for_dtype(other, self.dtype):
             other = np.datetime64("NaT", "ns")
         elif isinstance(other, (datetime, np.datetime64, date)):
-            other = self._box_func(other)
-            if getattr(other, "tz") is not None:
+            other = Timestamp(other)
+            if other.tz is not None:
                 raise TypeError("cannot coerce a Timestamp with a tz on a naive Block")
             other = other.asm8
         elif hasattr(other, "dtype") and is_datetime64_dtype(other):
@@ -2293,10 +2293,6 @@ def _try_coerce_result(self, result):
             result = result.view("M8[ns]")
         return result
 
-    @property
-    def _box_func(self):
-        return tslibs.Timestamp
-
     def to_native_types(
         self, slicer=None, na_rep=None, date_format=None, quoting=None, **kwargs
     ):
@@ -2450,9 +2446,7 @@ def _try_coerce_args(self, other):
         if isinstance(other, ABCSeries):
             other = self._holder(other)
 
-        if isinstance(other, bool):
-            raise TypeError
-        elif is_datetime64_dtype(other):
+        if is_datetime64_dtype(other):
             # add the tz back
             other = self._holder(other, dtype=self.dtype)
 
@@ -2589,10 +2583,6 @@ def __init__(self, values, placement, ndim=None):
     def _holder(self):
         return TimedeltaArray
 
-    @property
-    def _box_func(self):
-        return lambda x: Timedelta(x, unit="ns")
-
     def _can_hold_element(self, element):
         tipo = maybe_infer_dtype_type(element)
         if tipo is not None:

From 1ae64ac396c93bb6ae199297c9179567ca906e34 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Tue, 16 Jul 2019 21:41:08 -0700
Subject: [PATCH 06/16] remove unnecessary

---
 pandas/core/internals/blocks.py | 13 +++----------
 1 file changed, 3 insertions(+), 10 deletions(-)

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 7b76b81c81fe4..7277ea1a4fb79 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -391,8 +391,9 @@ def apply(self, func, **kwargs):
         with np.errstate(all="ignore"):
             result = func(self.values, **kwargs)
         if not isinstance(result, Block):
+            # TODO: do we need this condition?  It could only fail if the user
+            #  passed a `func` that itself returned a Block
             result = self.make_block(values=_block_shape(result, ndim=self.ndim))
-
         return result
 
     def fillna(self, value, limit=None, inplace=False, downcast=None):
@@ -2442,15 +2443,7 @@ def _try_coerce_args(self, other):
         -------
         base-type other
         """
-
-        if isinstance(other, ABCSeries):
-            other = self._holder(other)
-
-        if is_datetime64_dtype(other):
-            # add the tz back
-            other = self._holder(other, dtype=self.dtype)
-
-        elif is_valid_nat_for_dtype(other, self.dtype):
+        if is_valid_nat_for_dtype(other, self.dtype):
             other = np.datetime64("NaT", "ns")
         elif isinstance(other, self._holder):
             if not tz_compare(other.tz, self.values.tz):

From 512855a6e3393a72187ba0c7d41a9698209972fb Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 17 Jul 2019 08:42:57 -0700
Subject: [PATCH 07/16] remove _coerce_values

---
 pandas/core/internals/blocks.py | 23 ++---------------------
 1 file changed, 2 insertions(+), 21 deletions(-)

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 7277ea1a4fb79..7467cada0919c 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -708,20 +708,6 @@ def _try_cast_result(self, result, dtype=None):
         # may need to change the dtype here
         return maybe_downcast_to_dtype(result, dtype)
 
-    def _coerce_values(self, values):
-        """
-        Coerce values (usually derived from self.values) for an operation.
-
-        Parameters
-        ----------
-        values : ndarray or ExtensionArray
-
-        Returns
-        -------
-        ndarray or ExtensionArray
-        """
-        return _block_shape(values, ndim=self.ndim)
-
     def _try_coerce_args(self, other):
         """ provide coercion to our input arguments """
 
@@ -784,7 +770,7 @@ def replace(
 
         # try to replace, if we raise an error, convert to ObjectBlock and
         # retry
-        values = self._coerce_values(self.values)
+        values = self.values
         try:
             to_replace = self._try_coerce_args(to_replace)
         except (TypeError, ValueError):
@@ -891,7 +877,6 @@ def setitem(self, indexer, value):
                     b = self.astype(dtype)
                     return b.setitem(indexer, value)
         else:
-            values = self._coerce_values(values)
             # can keep its own dtype
             if hasattr(value, "dtype") and is_dtype_equal(values.dtype, value.dtype):
                 dtype = self.dtype
@@ -1216,7 +1201,6 @@ def _interpolate_with_fill(
                     return [self.copy()]
 
         values = self.values if inplace else self.values.copy()
-        values = self._coerce_values(values)
         fill_value = self._try_coerce_args(fill_value)
         values = missing.interpolate_2d(
             values,
@@ -1424,7 +1408,6 @@ def func(cond, values, other):
         else:
             # see if we can operate on the entire block, or need item-by-item
             # or if we are a single block (ndim == 1)
-            values = self._coerce_values(values)
             try:
                 result = func(cond, values, other)
             except TypeError:
@@ -1535,7 +1518,6 @@ def quantile(self, qs, interpolation="linear", axis=0):
             values = values[None, :]
         else:
             values = self.get_values()
-            values = self._coerce_values(values)
 
         is_empty = values.shape[axis] == 0
         orig_scalar = not is_list_like(qs)
@@ -1700,7 +1682,6 @@ def putmask(self, mask, new, align=True, inplace=False, axis=0, transpose=False)
         # use block's copy logic.
         # .values may be an Index which does shallow copy by default
         new_values = self.values if inplace else self.copy().values
-        new_values = self._coerce_values(new_values)
         new = self._try_coerce_args(new)
 
         if isinstance(new, np.ndarray) and len(new) == len(mask):
@@ -2405,7 +2386,7 @@ def get_values(self, dtype=None):
         """
         values = self.values
         if is_object_dtype(dtype):
-            values = values._box_values(values._data)
+            values = values.astype(object)
 
         values = np.asarray(values)
 

From 0b8bdba7be9fa799789904461f60e11d690754fc Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 17 Jul 2019 10:20:27 -0700
Subject: [PATCH 08/16] comments

---
 pandas/core/internals/blocks.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index fa18c73e93e65..b57450e585b9f 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -1825,6 +1825,7 @@ def get_values(self, dtype=None):
             values = values.reshape((1,) + values.shape)
         return values
 
+    # TODO: should this reshape?
     def to_dense(self):
         return np.asarray(self.values)
 
@@ -2402,6 +2403,7 @@ def get_values(self, dtype=None):
             values = values.reshape(1, -1)
         return values
 
+    # TODO: should this reshape?
     def to_dense(self):
         # we request M8[ns] dtype here, even though it discards tzinfo,
         # as lots of code (e.g. anything using values_from_object)

From 6500ed8d1789a900542056cc50d4943c291bcca7 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Tue, 23 Jul 2019 17:30:32 -0700
Subject: [PATCH 09/16] Cleanup

---
 pandas/core/internals/blocks.py | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 85f9f51ccb48b..9114ac9ac24a8 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -390,9 +390,8 @@ def apply(self, func, **kwargs):
         with np.errstate(all="ignore"):
             result = func(self.values, **kwargs)
         if not isinstance(result, Block):
-            # TODO: do we need this condition?  It could only fail if the user
-            #  passed a `func` that itself returned a Block
             result = self.make_block(values=_block_shape(result, ndim=self.ndim))
+
         return result
 
     def fillna(self, value, limit=None, inplace=False, downcast=None):
@@ -1829,7 +1828,6 @@ def get_values(self, dtype=None):
             values = values.reshape((1,) + values.shape)
         return values
 
-    # TODO: should this reshape?
     def to_dense(self):
         return np.asarray(self.values)
 
@@ -2407,7 +2405,6 @@ def get_values(self, dtype=None):
             values = values.reshape(1, -1)
         return values
 
-    # TODO: should this reshape?
     def to_dense(self):
         # we request M8[ns] dtype here, even though it discards tzinfo,
         # as lots of code (e.g. anything using values_from_object)

From 79128ede808fabd71c7f1c6017d6376c0f9076aa Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Tue, 23 Jul 2019 18:31:54 -0700
Subject: [PATCH 10/16] use extract_array

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

diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index 44d03a386e90a..70fc157a9dd5b 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -34,7 +34,6 @@ class providing the base-class of operations.
     is_numeric_dtype,
     is_scalar,
 )
-from pandas.core.dtypes.generic import ABCDatetimeArray
 from pandas.core.dtypes.missing import isna, notna
 
 from pandas.api.types import is_datetime64_dtype, is_integer_dtype, is_object_dtype
@@ -52,6 +51,7 @@ class providing the base-class of operations.
 from pandas.core.generic import NDFrame
 from pandas.core.groupby import base
 from pandas.core.index import CategoricalIndex, Index, MultiIndex
+from pandas.core.internals.arrays import extract_array
 from pandas.core.series import Series
 from pandas.core.sorting import get_group_index_sorter
 
@@ -804,10 +804,7 @@ def _try_cast(self, result, obj, numeric_only=False):
                 # Prior results _may_ have been generated in UTC.
                 # Ensure we localize to UTC first before converting
                 # to the target timezone
-                if isinstance(obj, ABCDatetimeArray):
-                    arr = obj
-                else:
-                    arr = obj._values
+                arr = extract_array(obj)
                 try:
                     result = arr._from_sequence(
                         result, dtype="datetime64[ns, UTC]"

From 5d73147eb958dbea4059583f64467e83c420339b Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 24 Jul 2019 09:29:47 -0700
Subject: [PATCH 11/16] blackify

---
 pandas/core/groupby/groupby.py | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/pandas/core/groupby/groupby.py b/pandas/core/groupby/groupby.py
index 70fc157a9dd5b..d4fdaa13ef712 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -806,9 +806,7 @@ def _try_cast(self, result, obj, numeric_only=False):
                 # to the target timezone
                 arr = extract_array(obj)
                 try:
-                    result = arr._from_sequence(
-                        result, dtype="datetime64[ns, UTC]"
-                    )
+                    result = arr._from_sequence(result, dtype="datetime64[ns, UTC]")
                     result = result.astype(dtype)
                 except TypeError:
                     # _try_cast was called at a point where the result

From 6ed302ceff777986f4f6e8403a7743dff4282f20 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Wed, 24 Jul 2019 09:30:03 -0700
Subject: [PATCH 12/16] isort

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

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 9114ac9ac24a8..87dd04acf7e3f 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -7,7 +7,7 @@
 
 import numpy as np
 
-from pandas._libs import NaT, lib, tslib, tslibs, Timestamp
+from pandas._libs import NaT, Timestamp, lib, tslib, tslibs
 import pandas._libs.internals as libinternals
 from pandas._libs.tslibs import Timedelta, conversion
 from pandas._libs.tslibs.timezones import tz_compare

From df6ac0ab73368b422a5216b791d9df596a836157 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Thu, 25 Jul 2019 13:23:35 -0700
Subject: [PATCH 13/16] update import

---
 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 d4fdaa13ef712..0dff6b4f7fd99 100644
--- a/pandas/core/groupby/groupby.py
+++ b/pandas/core/groupby/groupby.py
@@ -47,11 +47,11 @@ class providing the base-class of operations.
     SpecificationError,
 )
 import pandas.core.common as com
+from pandas.core.construction import extract_array
 from pandas.core.frame import DataFrame
 from pandas.core.generic import NDFrame
 from pandas.core.groupby import base
 from pandas.core.index import CategoricalIndex, Index, MultiIndex
-from pandas.core.internals.arrays import extract_array
 from pandas.core.series import Series
 from pandas.core.sorting import get_group_index_sorter
 

From 58489379d8a4d1d3862d877954b6d8f43b20925e Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Thu, 25 Jul 2019 15:43:25 -0700
Subject: [PATCH 14/16] Fix incorrect test

---
 pandas/tests/indexing/test_datetime.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/pandas/tests/indexing/test_datetime.py b/pandas/tests/indexing/test_datetime.py
index 31e9cff68445e..fb8f62d7a06c5 100644
--- a/pandas/tests/indexing/test_datetime.py
+++ b/pandas/tests/indexing/test_datetime.py
@@ -51,7 +51,7 @@ def test_indexing_with_datetime_tz(self):
         # indexing
         result = df.iloc[1]
         expected = Series(
-            [Timestamp("2013-01-02 00:00:00-0500", tz="US/Eastern"), np.nan, np.nan],
+            [Timestamp("2013-01-02 00:00:00-0500", tz="US/Eastern"), pd.NaT, pd.NaT],
             index=list("ABC"),
             dtype="object",
             name=1,
@@ -59,7 +59,7 @@ def test_indexing_with_datetime_tz(self):
         tm.assert_series_equal(result, expected)
         result = df.loc[1]
         expected = Series(
-            [Timestamp("2013-01-02 00:00:00-0500", tz="US/Eastern"), np.nan, np.nan],
+            [Timestamp("2013-01-02 00:00:00-0500", tz="US/Eastern"), pd.NaT, pd.NaT],
             index=list("ABC"),
             dtype="object",
             name=1,

From 53585b2d8a59aee78980466d05fa8c21d901e41a Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Fri, 26 Jul 2019 09:17:46 -0700
Subject: [PATCH 15/16] comment

---
 pandas/core/internals/blocks.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 80a5288e78be6..ef12f3a96ac96 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -2471,6 +2471,7 @@ def _try_coerce_result(self, result):
         """ reverse of try_coerce_args """
         if isinstance(result, np.ndarray):
             if result.ndim == 2:
+                # kludge for 2D blocks with 1D EAs
                 result = result[0, :]
             if result.dtype == np.float64:
                 # needed for post-groupby.median

From ba043bbef3e20a8f4ea021e1f60cd6fa6052d6b1 Mon Sep 17 00:00:00 2001
From: jbrockmendel <jbrockmendel@gmail.com>
Date: Fri, 26 Jul 2019 09:55:54 -0700
Subject: [PATCH 16/16] post merge fix

---
 pandas/core/internals/blocks.py | 1 -
 1 file changed, 1 deletion(-)

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index ef12f3a96ac96..4ca867b1088e7 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -868,7 +868,6 @@ def setitem(self, indexer, value):
         if self._can_hold_element(value):
             value = self._try_coerce_args(value)
 
-            values = self._coerce_values(values)
             # can keep its own dtype
             if hasattr(value, "dtype") and is_dtype_equal(values.dtype, value.dtype):
                 dtype = self.dtype