mypy fixup

Author: jbrockmendel

pandas/core/arrays/datetimelike.py

@@ -157,6 +157,8 @@
         Sequence,
     )
 
+    from pandas._typing import TimeUnit
+
     from pandas import Index
     from pandas.core.arrays import (
         DatetimeArray,
@@ -2114,7 +2116,7 @@ def _creso(self) -> int:
         return get_unit_from_dtype(self._ndarray.dtype)
 
     @cache_readonly
-    def unit(self) -> str:
+    def unit(self) -> TimeUnit:
         """
         The precision unit of the datetime data.
 

pandas/core/resample.py

@@ -3095,7 +3095,7 @@ def asfreq(
 
         new_obj.index = _asfreq_compat(obj.index, freq)
     else:
-        unit = None
+        unit: TimeUnit = "ns"
         if isinstance(obj.index, DatetimeIndex):
             # TODO: should we disallow non-DatetimeIndex?
             unit = obj.index.unit