ArrayData: Allow defining array(s) on construction

Currently, the constructor does not allow to define any arrays to set
when constructing a new node, so one is forced to multi line code:

    node = ArrayData()
    node.set_array('a', np.array([1, 2]))
    node.set_array('b', np.array([3, 4]))

This commit allows initialization upon construction simplifying the code
above to:

    node = ArrayData({'a': np.array([1, 2]), 'b': np.array([3, 4])})

Note that it is also possible to pass a single array to the constructor,
in which case the array name is taken from the `default_array_name`
class attribute.

For backwards compatibility, it remains possible to construct an
`ArrayData` without any arrays.

aiida/orm/nodes/data/array/array.py

@@ -39,15 +39,32 @@ class ArrayData(Data):
       cache with the :py:meth:`.clear_internal_cache` method.
     """
     array_prefix = 'array|'
+    default_array_name = 'default'
 
-    def __init__(self, **kwargs):
+    def __init__(self, arrays: 'ndarray' | dict[str, 'ndarray'] | None = None, **kwargs):
         """Construct a new instance and set one or multiple numpy arrays.
 
-        :param arrays: A single numpy array, or a dictionary of numpy arrays to store.
+        :param arrays: An optional single numpy array, or dictionary of numpy arrays to store.
         """
+        import numpy
+
         super().__init__(**kwargs)
         self._cached_arrays: dict[str, 'ndarray'] = {}
 
+        arrays = arrays if arrays is not None else {}
+
+        if isinstance(arrays, numpy.ndarray):
+            arrays = {self.default_array_name: arrays}
+
+        if (
+            not isinstance(arrays, dict)  # type: ignore[redundant-expr]
+            or any(not isinstance(a, numpy.ndarray) for a in arrays.values())
+        ):
+            raise TypeError(f'`arrays` should be a single numpy array or dictionary of numpy arrays but got: {arrays}')
+
+        for key, value in arrays.items():
+            self.set_array(key, value)
+
     def initialize(self):
         super().initialize()
         self._cached_arrays = {}

tests/orm/nodes/data/test_array.py

@@ -26,3 +26,20 @@ def test_read_stored():
 
     loaded = load_node(node.uuid)
     assert numpy.array_equal(loaded.get_array('array'), array)
+
+
+def test_constructor():
+    """Test the various construction options."""
+    node = ArrayData()
+    assert node.get_arraynames() == []
+
+    arrays = numpy.array([1, 2])
+    node = ArrayData(arrays)
+    assert node.get_arraynames() == [ArrayData.default_array_name]
+    assert (node.get_array(ArrayData.default_array_name) == arrays).all()
+
+    arrays = {'a': numpy.array([1, 2]), 'b': numpy.array([3, 4])}
+    node = ArrayData(arrays)
+    assert sorted(node.get_arraynames()) == ['a', 'b']
+    assert (node.get_array('a') == arrays['a']).all()
+    assert (node.get_array('b') == arrays['b']).all()