REF: check can_hold_element instead of try/except (#27298)

Author: jbrockmendel

pandas/core/internals/blocks.py

@@ -7,7 +7,7 @@
 
 import numpy as np
 
-from pandas._libs import lib, tslib, tslibs
+from pandas._libs import NaT, lib, tslib, tslibs
 import pandas._libs.internals as libinternals
 from pandas._libs.tslibs import Timedelta, conversion, is_null_datetimelike
 from pandas.util._validators import validate_bool_kwarg
@@ -405,33 +405,29 @@ def fillna(self, value, limit=None, inplace=False, downcast=None):
             else:
                 return self.copy()
 
-        # fillna, but if we cannot coerce, then try again as an ObjectBlock
-        try:
-            # Note: we only call try_coerce_args to let it raise
-            self._try_coerce_args(value)
-        except (TypeError, ValueError):
-
-            # we can't process the value, but nothing to do
-            if not mask.any():
-                return self if inplace else self.copy()
-
-            # operate column-by-column
-            def f(m, v, i):
-                block = self.coerce_to_target_dtype(value)
-
-                # slice out our block
-                if i is not None:
-                    block = block.getitem_block(slice(i, i + 1))
-                return block.fillna(value, limit=limit, inplace=inplace, downcast=None)
-
-            return self.split_and_operate(mask, f, inplace)
-        else:
+        if self._can_hold_element(value):
+            # equivalent: self._try_coerce_args(value) would not raise
             blocks = self.putmask(mask, value, inplace=inplace)
             blocks = [
                 b.make_block(values=self._try_coerce_result(b.values)) for b in blocks
             ]
             return self._maybe_downcast(blocks, downcast)
 
+        # we can't process the value, but nothing to do
+        if not mask.any():
+            return self if inplace else self.copy()
+
+        # operate column-by-column
+        def f(m, v, i):
+            block = self.coerce_to_target_dtype(value)
+
+            # slice out our block
+            if i is not None:
+                block = block.getitem_block(slice(i, i + 1))
+            return block.fillna(value, limit=limit, inplace=inplace, downcast=None)
+
+        return self.split_and_operate(mask, f, inplace)
+
     def split_and_operate(self, mask, f, inplace):
         """
         split the block per-column, and apply the callable f
@@ -2275,7 +2271,13 @@ def _can_hold_element(self, element):
         tipo = maybe_infer_dtype_type(element)
         if tipo is not None:
             return tipo == _NS_DTYPE or tipo == np.int64
-        return is_integer(element) or isinstance(element, datetime) or isna(element)
+        if isinstance(element, datetime):
+            return element.tzinfo is None
+        if is_integer(element):
+            return element == tslibs.iNaT
+
+        # TODO: shouldnt we exclude timedelta64("NaT")?  See GH#27297
+        return isna(element)
 
     def _coerce_values(self, values):
         return values.view("i8")
@@ -2627,6 +2629,8 @@ def _can_hold_element(self, element):
         tipo = maybe_infer_dtype_type(element)
         if tipo is not None:
             return issubclass(tipo.type, (np.timedelta64, np.int64))
+        if element is NaT:
+            return True
         return is_integer(element) or isinstance(
             element, (timedelta, np.timedelta64, np.int64)
         )