From 21bcfd09c8aea319cf41f806f2daa555d28eb009 Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Sun, 9 Jul 2023 13:17:27 -0700
Subject: [PATCH 1/2] REF: share block methods

---
 pandas/core/internals/blocks.py | 49 +++++++++++++++++++--------------
 1 file changed, 28 insertions(+), 21 deletions(-)

diff --git a/pandas/core/internals/blocks.py b/pandas/core/internals/blocks.py
index 4480a1a0c6746..f34a9f7590a5e 100644
--- a/pandas/core/internals/blocks.py
+++ b/pandas/core/internals/blocks.py
@@ -156,10 +156,34 @@ class Block(PandasObject):
 
     __slots__ = ()
     is_numeric = False
-    is_object = False
-    is_extension = False
-    _can_consolidate = True
-    _validate_ndim = True
+
+    @final
+    @cache_readonly
+    def _validate_ndim(self) -> bool:
+        """
+        We validate dimension for blocks that can hold 2D values, which for now
+        means numpy dtypes or DatetimeTZDtype.
+        """
+        dtype = self.dtype
+        return not isinstance(dtype, ExtensionDtype) or isinstance(
+            dtype, DatetimeTZDtype
+        )
+
+    @final
+    @cache_readonly
+    def is_object(self) -> bool:
+        return self.values.dtype == _dtype_obj
+
+    @final
+    @cache_readonly
+    def is_extension(self) -> bool:
+        return not lib.is_np_dtype(self.values.dtype)
+
+    @final
+    @cache_readonly
+    def _can_consolidate(self) -> bool:
+        # We _could_ consolidate for DatetimeTZDtype but don't for now.
+        return not self.is_extension
 
     @final
     @cache_readonly
@@ -1905,10 +1929,6 @@ class ExtensionBlock(libinternals.Block, EABackedBlock):
     ExtensionArrays are limited to 1-D.
     """
 
-    _can_consolidate = False
-    _validate_ndim = False
-    is_extension = True
-
     values: ExtensionArray
 
     def fillna(
@@ -2172,10 +2192,6 @@ def is_numeric(self) -> bool:  # type: ignore[override]
 
         return kind in "fciub"
 
-    @cache_readonly
-    def is_object(self) -> bool:  # type: ignore[override]
-        return self.values.dtype.kind == "O"
-
 
 class NumericBlock(NumpyBlock):
     # this Block type is kept for backwards-compatibility
@@ -2196,12 +2212,6 @@ class NDArrayBackedExtensionBlock(libinternals.NDArrayBackedBlock, EABackedBlock
 
     values: NDArrayBackedExtensionArray
 
-    # error: Signature of "is_extension" incompatible with supertype "Block"
-    @cache_readonly
-    def is_extension(self) -> bool:  # type: ignore[override]
-        # i.e. datetime64tz, PeriodDtype
-        return not isinstance(self.dtype, np.dtype)
-
     @property
     def is_view(self) -> bool:
         """return a boolean if I am possibly a view"""
@@ -2239,9 +2249,6 @@ class DatetimeTZBlock(DatetimeLikeBlock):
     values: DatetimeArray
 
     __slots__ = ()
-    is_extension = True
-    _validate_ndim = True
-    _can_consolidate = False
 
     # Don't use values_for_json from DatetimeLikeBlock since it is
     # an invalid optimization here(drop the tz)

From 50fb950870f25fb6d65f94ddacb6ab336e70d055 Mon Sep 17 00:00:00 2001
From: Brock <jbrockmendel@gmail.com>
Date: Mon, 10 Jul 2023 10:26:19 -0700
Subject: [PATCH 2/2] Remove unnecessary test

---
 pandas/tests/extension/test_external_block.py | 39 -------------------
 1 file changed, 39 deletions(-)
 delete mode 100644 pandas/tests/extension/test_external_block.py

diff --git a/pandas/tests/extension/test_external_block.py b/pandas/tests/extension/test_external_block.py
deleted file mode 100644
index 1b5b46c6a01bb..0000000000000
--- a/pandas/tests/extension/test_external_block.py
+++ /dev/null
@@ -1,39 +0,0 @@
-import numpy as np
-import pytest
-
-from pandas._libs.internals import BlockPlacement
-import pandas.util._test_decorators as td
-
-import pandas as pd
-from pandas.core.internals import BlockManager
-from pandas.core.internals.blocks import ExtensionBlock
-
-pytestmark = td.skip_array_manager_invalid_test
-
-
-class CustomBlock(ExtensionBlock):
-    _holder = np.ndarray
-
-    # Cannot override final attribute "_can_hold_na"
-    @property  # type: ignore[misc]
-    def _can_hold_na(self) -> bool:
-        return False
-
-
-@pytest.fixture
-def df():
-    df1 = pd.DataFrame({"a": [1, 2, 3]})
-    blocks = df1._mgr.blocks
-    values = np.arange(3, dtype="int64")
-    bp = BlockPlacement(slice(1, 2))
-    custom_block = CustomBlock(values, placement=bp, ndim=2)
-    blocks = blocks + (custom_block,)
-    block_manager = BlockManager(blocks, [pd.Index(["a", "b"]), df1.index])
-    return pd.DataFrame(block_manager)
-
-
-def test_concat_axis1(df):
-    # GH17954
-    df2 = pd.DataFrame({"c": [0.1, 0.2, 0.3]})
-    res = pd.concat([df, df2], axis=1)
-    assert isinstance(res._mgr.blocks[1], CustomBlock)