better get_mask_array_type

Author: jreback

pandas/core/arrays/_mask.py

@@ -1,8 +1,12 @@
 """A boolean mask interace.
 
 This module provides an interface to a numpy / pyarrow boolean mask.
+This is limited as not all of the implementations can hold NA, so
+for consistency this is an internal.
 """
 
+_MaskArrayType = None
+
 
 class _MaskArray:
     _typ = "maskarray"
@@ -21,7 +25,14 @@ def _reduce(self, method, skipna=True, **kwargs):
 
 
 def get_mask_array_type():
-    # TODO: protect imports
+    """Set the mask array type to use, we need to do
+    this after all modules are imported as the implementations
+    e.g. pyarrow depend on pandas being importable
+    """
+    global _MaskArrayType
+
+    if _MaskArrayType is not None:
+        return _MaskArrayType
 
     # if ArrowBoolArray is available use it
     # otherwise use the NumpyMask
@@ -37,4 +48,5 @@ class MaskArray(_MaskArray, ArrowBoolArray):
         class MaskArray(_MaskArray, NumpyBoolArray):
             pass
 
-    return MaskArray
+    _MaskArrayType = MaskArray
+    return _MaskArrayType

pandas/core/arrays/_numpy_bool.py

@@ -3,6 +3,7 @@
 """
 
 import numpy as np
+
 from pandas.core.arrays import ExtensionArray
 
 

pandas/tests/dtypes/test_common.py

@@ -527,8 +527,6 @@ def test_is_bool_dtype():
     assert com.is_bool_dtype(np.bool)
     assert com.is_bool_dtype(np.array([True, False]))
     assert com.is_bool_dtype(pd.Index([True, False]))
-
-    # TODO: hack-a-minute
     assert com.is_bool_dtype(
         get_mask_array_type()._from_sequence([True, False]))