Implement UInt64 handling, tests, and docs

Author: TomAugspurger

doc/source/whatsnew/v0.24.0.rst

@@ -1324,6 +1324,7 @@ Datetimelike
 - Bug in :func:`to_datetime` where ``box`` and ``utc`` arguments were ignored when passing a :class:`DataFrame` or ``dict`` of unit mappings (:issue:`23760`)
 - Bug in :attr:`Series.dt` where the cache would not update properly after an in-place operation (:issue:`24408`)
 - Bug in :class:`PeriodIndex` where comparisons against an array-like object with length 1 failed to raise ``ValueError`` (:issue:`23078`)
+- Bug in :meth:`DatetimeIndex.astype`, :meth:`PeriodIndex.astype` and :meth:`TimedeltaIndex.astype` ignoring the sign of the ``dtype`` for unsigned integer dtypes (:issue:`24405`).
 
 Timedelta
 ^^^^^^^^^

pandas/core/arrays/datetimelike.py

@@ -21,7 +21,8 @@
     is_datetime64_dtype, is_datetime64tz_dtype, is_datetime_or_timedelta_dtype,
     is_dtype_equal, is_extension_array_dtype, is_float_dtype, is_integer_dtype,
     is_list_like, is_object_dtype, is_offsetlike, is_period_dtype,
-    is_string_dtype, is_timedelta64_dtype, needs_i8_conversion, pandas_dtype)
+    is_string_dtype, is_timedelta64_dtype, is_unsigned_integer_dtype,
+    needs_i8_conversion, pandas_dtype)
 from pandas.core.dtypes.generic import ABCDataFrame, ABCIndexClass, ABCSeries
 from pandas.core.dtypes.missing import isna
 
@@ -419,6 +420,11 @@ def astype(self, dtype, copy=True):
             # we deliberately ignore int32 vs. int64 here.
             # See https://github.com/pandas-dev/pandas/issues/24381 for more.
             values = self.asi8
+
+            if is_unsigned_integer_dtype(dtype):
+                # Again, we ignore int32 vs. int64
+                values = values.view("uint64")
+
             if copy:
                 values = values.copy()
             return values

pandas/core/indexes/base.py

@@ -739,8 +739,9 @@ def view(self, cls=None):
         Parameters
         ----------
         dtype : numpy dtype or pandas type
-            Note that any integer `dtype` is treated as ``'int64'``,
-            regardless of the sign and size.
+            Note that any signed integer `dtype` is treated as ``'int64'``,
+            and any unsigned integer `dtype` is treated as ``'uint64'``,
+            regardless of the size.
         copy : bool, default True
             By default, astype always returns a newly allocated object.
             If copy is set to False and internal requirements on dtype are

pandas/tests/indexes/datetimes/test_astype.py

@@ -33,6 +33,15 @@ def test_astype(self):
         tm.assert_index_equal(result, Index(rng.asi8))
         tm.assert_numpy_array_equal(result.values, rng.asi8)
 
+    def test_astype_uint(self):
+        arr = date_range('2000', periods=2)
+        expected = pd.UInt64Index(
+            np.array([946684800000000000, 946771200000000000], dtype="uint64")
+        )
+
+        tm.assert_index_equal(arr.astype("uint64"), expected)
+        tm.assert_index_equal(arr.astype("uint32"), expected)
+
     def test_astype_with_tz(self):
 
         # with tz

pandas/tests/indexes/period/test_astype.py

@@ -41,6 +41,12 @@ def test_astype_conversion(self):
         tm.assert_index_equal(result, Index(idx.asi8))
         tm.assert_numpy_array_equal(result.values, idx.asi8)
 
+    def test_astype_uint(self):
+        arr = period_range('2000', periods=2)
+        expected = pd.UInt64Index(np.array([10957, 10958], dtype='uint64'))
+        tm.assert_index_equal(arr.astype("uint64"), expected)
+        tm.assert_index_equal(arr.astype("uint32"), expected)
+
     def test_astype_object(self):
         idx = pd.PeriodIndex([], freq='M')
 

pandas/tests/indexes/timedeltas/test_astype.py

@@ -54,6 +54,15 @@ def test_astype(self):
         tm.assert_index_equal(result, Index(rng.asi8))
         tm.assert_numpy_array_equal(rng.asi8, result.values)
 
+    def test_astype_uint(self):
+        arr = timedelta_range('1H', periods=2)
+        expected = pd.UInt64Index(
+            np.array([3600000000000, 90000000000000], dtype="uint64")
+        )
+
+        tm.assert_index_equal(arr.astype("uint64"), expected)
+        tm.assert_index_equal(arr.astype("uint32"), expected)
+
     def test_astype_timedelta64(self):
         # GH 13149, GH 13209
         idx = TimedeltaIndex([1e14, 'NaT', NaT, np.NaN])