From 527f196c1c18da11b4fc3bf629fde5a5ede0f5fd Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Mon, 15 Feb 2021 18:04:56 -0800
Subject: [PATCH 1/2] BUG: DataFrame.append

---
 pandas/core/internals/concat.py | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/pandas/core/internals/concat.py b/pandas/core/internals/concat.py
index a2c930f6d9b22..01d8cde3e9af2 100644
--- a/pandas/core/internals/concat.py
+++ b/pandas/core/internals/concat.py
@@ -291,9 +291,7 @@ def get_reindexed_values(self, empty_dtype: DtypeObj, upcasted_na) -> ArrayLike:
                     if len(values) and values[0] is None:
                         fill_value = None
 
-                if is_datetime64tz_dtype(blk_dtype) or is_datetime64tz_dtype(
-                    empty_dtype
-                ):
+                if is_datetime64tz_dtype(empty_dtype):
                     # TODO(EA2D): special case unneeded with 2D EAs
                     i8values = np.full(self.shape[1], fill_value.value)
                     return DatetimeArray(i8values, dtype=empty_dtype)
@@ -302,9 +300,8 @@ def get_reindexed_values(self, empty_dtype: DtypeObj, upcasted_na) -> ArrayLike:
                 elif is_extension_array_dtype(blk_dtype):
                     pass
                 elif is_extension_array_dtype(empty_dtype):
-                    missing_arr = empty_dtype.construct_array_type()._from_sequence(
-                        [], dtype=empty_dtype
-                    )
+                    cls = empty_dtype.construct_array_type()
+                    missing_arr = cls._from_sequence([], dtype=empty_dtype)
                     ncols, nrows = self.shape
                     assert ncols == 1, ncols
                     empty_arr = -1 * np.ones((nrows,), dtype=np.intp)

From 3706470759ea6247dd96d2c6eba425a61a90e760 Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Fri, 26 Feb 2021 09:35:36 -0800
Subject: [PATCH 2/2] REF: tighten types in maybe_downcast

---
 pandas/core/dtypes/cast.py | 16 +++++++---------
 1 file changed, 7 insertions(+), 9 deletions(-)

diff --git a/pandas/core/dtypes/cast.py b/pandas/core/dtypes/cast.py
index b30dbe32eec4b..8e5f386ae8d43 100644
--- a/pandas/core/dtypes/cast.py
+++ b/pandas/core/dtypes/cast.py
@@ -94,7 +94,6 @@
     PeriodDtype,
 )
 from pandas.core.dtypes.generic import (
-    ABCDataFrame,
     ABCExtensionArray,
     ABCIndex,
     ABCSeries,
@@ -233,19 +232,15 @@ def _disallow_mismatched_datetimelike(value, dtype: DtypeObj):
         raise TypeError(f"Cannot cast {repr(value)} to {dtype}")
 
 
-def maybe_downcast_to_dtype(result, dtype: Union[str, np.dtype]):
+def maybe_downcast_to_dtype(
+    result: ArrayLike, dtype: Union[str, np.dtype]
+) -> ArrayLike:
     """
     try to cast to the specified dtype (e.g. convert back to bool/int
     or could be an astype of float64->float32
     """
     do_round = False
 
-    if is_scalar(result):
-        return result
-    elif isinstance(result, ABCDataFrame):
-        # occurs in pivot_table doctest
-        return result
-
     if isinstance(dtype, str):
         if dtype == "infer":
             inferred_type = lib.infer_dtype(ensure_object(result), skipna=False)
@@ -265,6 +260,7 @@ def maybe_downcast_to_dtype(result, dtype: Union[str, np.dtype]):
                     do_round = True
 
             else:
+                # TODO: complex?  what if result is already non-object?
                 dtype = "object"
 
         dtype = np.dtype(dtype)
@@ -296,7 +292,9 @@ def maybe_downcast_to_dtype(result, dtype: Union[str, np.dtype]):
     return result
 
 
-def maybe_downcast_numeric(result, dtype: DtypeObj, do_round: bool = False):
+def maybe_downcast_numeric(
+    result: ArrayLike, dtype: DtypeObj, do_round: bool = False
+) -> ArrayLike:
     """
     Subset of maybe_downcast_to_dtype restricted to numeric dtypes.