BUG: maybe_promote with dt64tz and mismatched NA (#39743)

Author: jbrockmendel

pandas/core/dtypes/cast.py

@@ -24,7 +24,7 @@
 
 import numpy as np
 
-from pandas._libs import lib, missing as libmissing, tslib
+from pandas._libs import lib, tslib
 from pandas._libs.tslibs import (
     NaT,
     OutOfBoundsDatetime,
@@ -86,7 +86,12 @@
     ABCSeries,
 )
 from pandas.core.dtypes.inference import is_list_like
-from pandas.core.dtypes.missing import is_valid_na_for_dtype, isna, notna
+from pandas.core.dtypes.missing import (
+    is_valid_na_for_dtype,
+    isna,
+    na_value_for_dtype,
+    notna,
+)
 
 if TYPE_CHECKING:
     from pandas import Series
@@ -529,16 +534,26 @@ def maybe_promote(dtype: np.dtype, fill_value=np.nan):
         dtype = np.dtype(object)
         return dtype, fill_value
 
+    kinds = ["i", "u", "f", "c", "m", "M"]
+    if is_valid_na_for_dtype(fill_value, dtype) and dtype.kind in kinds:
+        dtype = ensure_dtype_can_hold_na(dtype)
+        fv = na_value_for_dtype(dtype)
+        return dtype, fv
+
+    elif isna(fill_value):
+        dtype = np.dtype(object)
+        if fill_value is None:
+            # but we retain e.g. pd.NA
+            fill_value = np.nan
+        return dtype, fill_value
+
     # returns tuple of (dtype, fill_value)
     if issubclass(dtype.type, np.datetime64):
         if isinstance(fill_value, datetime) and fill_value.tzinfo is not None:
             # Trying to insert tzaware into tznaive, have to cast to object
             dtype = np.dtype(np.object_)
-        elif is_integer(fill_value) or (is_float(fill_value) and not isna(fill_value)):
+        elif is_integer(fill_value) or is_float(fill_value):
             dtype = np.dtype(np.object_)
-        elif is_valid_na_for_dtype(fill_value, dtype):
-            # e.g. pd.NA, which is not accepted by Timestamp constructor
-            fill_value = np.datetime64("NaT", "ns")
         else:
             try:
                 fill_value = Timestamp(fill_value).to_datetime64()
@@ -547,14 +562,11 @@ def maybe_promote(dtype: np.dtype, fill_value=np.nan):
     elif issubclass(dtype.type, np.timedelta64):
         if (
             is_integer(fill_value)
-            or (is_float(fill_value) and not np.isnan(fill_value))
+            or is_float(fill_value)
             or isinstance(fill_value, str)
         ):
             # TODO: What about str that can be a timedelta?
             dtype = np.dtype(np.object_)
-        elif is_valid_na_for_dtype(fill_value, dtype):
-            # e.g pd.NA, which is not accepted by the  Timedelta constructor
-            fill_value = np.timedelta64("NaT", "ns")
         else:
             try:
                 fv = Timedelta(fill_value)
@@ -615,17 +627,6 @@ def maybe_promote(dtype: np.dtype, fill_value=np.nan):
                 # e.g. mst is np.complex128 and dtype is np.complex64
                 dtype = mst
 
-    elif fill_value is None or fill_value is libmissing.NA:
-        # Note: we already excluded dt64/td64 dtypes above
-        if is_float_dtype(dtype) or is_complex_dtype(dtype):
-            fill_value = np.nan
-        elif is_integer_dtype(dtype):
-            dtype = np.dtype(np.float64)
-            fill_value = np.nan
-        else:
-            dtype = np.dtype(np.object_)
-            if fill_value is not libmissing.NA:
-                fill_value = np.nan
     else:
         dtype = np.dtype(np.object_)