Add getitem support.

scinum/__init__.py

@@ -840,7 +840,7 @@ def copy(
         if uncertainties is None:
             uncertainties = self.uncertainties
 
-        return self.__class__(nominal, uncertainties=uncertainties)
+        return self.__class__(nominal, uncertainties=uncertainties, **self._init_kwargs())  # type: ignore[arg-type] # noqa
 
     def get(
         self,
@@ -1113,6 +1113,19 @@ def __call__(
         # shorthand for get
         return self.get(direction=direction, names=names, unc=unc, factor=factor)
 
+    def __getitem__(self, key: int | slice) -> Number:
+        if not self.is_numpy:
+            raise TypeError("cannot index non-NumPy number")
+
+        return self.__class__(
+            self.nominal[key],
+            uncertainties={
+                name: (up[key], down[key])
+                for name, (up, down) in self.uncertainties.items()
+            },
+            **self._init_kwargs(),  # type: ignore[arg-type]
+        )
+
     def __float__(self) -> OutValueType:
         # extract nominal value
         return self.nominal

tests/test_number.py

@@ -150,6 +150,14 @@ def test_copy_numpy(self) -> None:
         self.assertEqual(len(num.uncertainties), 1)
         self.assertEqual(num.u(direction=UP).shape, (3,))
 
+    @if_numpy
+    def test_getitem_numpy(self) -> None:
+        num = Number(np.array([5, 27, 42]), 5)[1:]
+
+        self.assertEqual(tuple(num.nominal), (27, 42))
+        self.assertEqual(len(num.uncertainties), 1)
+        self.assertEqual(tuple(num.uncertainties["default"][0]), (5, 5))
+
     def test_string_formats(self) -> None:
         self.assertEqual(len(self.num.str()), 102)
         self.assertEqual(len(self.num.str("%.3f")), 126)