comments, typo

Author: jbrockmendel

pandas/core/arrays/timedeltas.py

@@ -240,7 +240,9 @@ def astype(self, dtype, copy=True):
         dtype = pandas_dtype(dtype)
 
         if is_timedelta64_dtype(dtype) and not is_timedelta64_ns_dtype(dtype):
-            # essentially this is division
+            # by pandas convention, converting to non-nano timedelta64
+            #  returns an int64-dtyped array with ints representing multiples
+            #  of the desired timedelta unit.  This is essentially division
             result = self._data.astype(dtype, copy=copy)
             if self._hasnans:
                 values = self._maybe_mask_results(result,

pandas/core/indexes/datetimelike.py

@@ -542,7 +542,9 @@ def astype(self, dtype, copy=True):
         if is_integer_dtype(dtype):
             dtype = np.dtype("int64")
 
-        return Index(new_values, dtype=dtype, name=self.name)
+        # pass copy=False because any copying will be done in the
+        #  _eadata.astype call above
+        return Index(new_values, dtype=dtype, name=self.name, copy=False)
 
     @Appender(DatetimeLikeArrayMixin._time_shift.__doc__)
     def _time_shift(self, periods, freq=None):

pandas/core/indexes/period.py

@@ -544,7 +544,7 @@ def astype(self, dtype, copy=True, how='start'):
         dtype = pandas_dtype(dtype)
 
         if is_datetime64_any_dtype(dtype):
-            # 'how' is index-speicifc, isn't part of the EA interface.
+            # 'how' is index-specific, isn't part of the EA interface.
             tz = getattr(dtype, 'tz', None)
             return self.to_timestamp(how=how).tz_localize(tz)