Makes NumericIndex constructor dtype aware

doc/source/whatsnew/v1.0.0.rst

@@ -336,6 +336,7 @@ Numeric
 - Bug in :class:`DataFrame` logical operations (`&`, `|`, `^`) not matching :class:`Series` behavior by filling NA values (:issue:`28741`)
 - Bug in :meth:`DataFrame.interpolate` where specifying axis by name references variable before it is assigned (:issue:`29142`)
 - Improved error message when using `frac` > 1 and `replace` = False (:issue:`27451`)
+- Bug in :class:`UInt64Index` precision loss while constructing from a list with values in the ``np.uint64`` range (:issue:`29526`)
 -
 
 Conversion

pandas/core/indexes/base.py

@@ -4026,30 +4026,6 @@ def _string_data_error(cls, data):
             "to explicitly cast to a numeric type"
         )
 
-    @classmethod
-    def _coerce_to_ndarray(cls, data):
-        """
-        Coerces data to ndarray.
-
-        Converts other iterables to list first and then to array.
-        Does not touch ndarrays.
-
-        Raises
-        ------
-        TypeError
-            When the data passed in is a scalar.
-        """
-
-        if not isinstance(data, (np.ndarray, Index)):
-            if data is None or is_scalar(data):
-                raise cls._scalar_data_error(data)
-
-            # other iterable of some kind
-            if not isinstance(data, (ABCSeries, list, tuple)):
-                data = list(data)
-            data = np.asarray(data)
-        return data
-
     def _coerce_scalar_to_index(self, item):
         """
         We need to coerce a scalar to a compat for our index type.

pandas/core/indexes/numeric.py

@@ -22,6 +22,7 @@
     ABCFloat64Index,
     ABCInt64Index,
     ABCRangeIndex,
+    ABCSeries,
     ABCUInt64Index,
 )
 from pandas.core.dtypes.missing import isna
@@ -56,8 +57,16 @@ def __new__(cls, data=None, dtype=None, copy=False, name=None, fastpath=None):
             if fastpath:
                 return cls._simple_new(data, name=name)
 
-        # is_scalar, generators handled in coerce_to_ndarray
-        data = cls._coerce_to_ndarray(data)
+        # Coerce to ndarray if not already ndarray or Index
+        if not isinstance(data, (np.ndarray, Index)):
+            if is_scalar(data):
+                raise cls._scalar_data_error(data)
+
+            # other iterable of some kind
+            if not isinstance(data, (ABCSeries, list, tuple)):
+                data = list(data)
+
+            data = np.asarray(data, dtype=dtype)
 
         if issubclass(data.dtype.type, str):
             cls._string_data_error(data)

pandas/tests/indexes/test_numeric.py

@@ -944,6 +944,11 @@ def test_constructor(self):
         res = Index(np.array([-1, 2 ** 63], dtype=object))
         tm.assert_index_equal(res, idx)
 
+        # https://github.com/pandas-dev/pandas/issues/29526
+        idx = UInt64Index([1, 2 ** 63 + 1], dtype=np.uint64)
+        res = Index([1, 2 ** 63 + 1], dtype=np.uint64)
+        tm.assert_index_equal(res, idx)
+
     def test_get_indexer(self, index_large):
         target = UInt64Index(np.arange(10).astype("uint64") * 5 + 2 ** 63)
         indexer = index_large.get_indexer(target)