XyData: 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 = XyData()
    node.set_x(np.array([1, 2]), 'name', unit')
    node.set_y(np.array([3, 4]), 'name', unit')

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

    node = XyData(
        np.array([1, 2]),
        np.array([3, 4]),
        x_name='name',
        x_unit='unit',
        y_names='name',
        y_units='unit'
    )

The units and names are intentionally made into keyword argument only
in order to prevent accidental swapping of values.

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

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

@@ -50,6 +50,34 @@ class XyData(ArrayData):
     Y arrays, which can be considered functions of X.
     """
 
+    def __init__(
+        self,
+        x_array: 'ndarray' | None = None,
+        y_arrays: 'ndarray' | list['ndarray'] | None = None,
+        *,
+        x_name: str | None = None,
+        x_units: str | None = None,
+        y_names: str | list[str] | None = None,
+        y_units: str | list[str] | None = None,
+        **kwargs
+    ):
+        """Construct a new instance, optionally setting the x and y arrays.
+
+        .. note:: If the ``x_array`` is specified, all other keywords need to be specified as well.
+
+        :param x_array: The x array.
+        :param y_arrays: The y arrays.
+        :param x_name: The name of the x array.
+        :param x_units: The unit of the x array.
+        :param y_names: The names of the y arrays.
+        :param y_units: The units of the y arrays.
+        """
+        super().__init__(**kwargs)
+
+        if x_array is not None:
+            self.set_x(x_array, x_name, x_units)  # type: ignore[arg-type]
+            self.set_y(y_arrays, y_names, y_units)  # type: ignore[arg-type]
+
     @staticmethod
     def _arrayandname_validator(array: 'ndarray', name: str, units: str) -> None:
         """

tests/orm/nodes/data/test_xy.py

@@ -0,0 +1,53 @@
+# -*- coding: utf-8 -*-
+###########################################################################
+# Copyright (c), The AiiDA team. All rights reserved.                     #
+# This file is part of the AiiDA code.                                    #
+#                                                                         #
+# The code is hosted on GitHub at https://github.com/aiidateam/aiida-core #
+# For further information on the license, see the LICENSE.txt file        #
+# For further information please visit http://www.aiida.net               #
+###########################################################################
+"""Tests for the :mod:`aiida.orm.nodes.data.array.xy` module."""
+import numpy
+import pytest
+
+from aiida.common.exceptions import NotExistent
+from aiida.orm import XyData, load_node
+
+
+def test_read_stored():
+    """Test reading an array from an ``XyData`` after storing and loading it."""
+    x_array = numpy.array([1, 2])
+    y_array = numpy.array([3, 4])
+    node = XyData(x_array, y_array, x_name='x_name', x_units='x_unit', y_names='y_name', y_units='y_units')
+
+    assert numpy.array_equal(node.get_x()[1], x_array)
+    assert numpy.array_equal(node.get_y()[0][1], y_array)
+
+    node.store()
+    assert numpy.array_equal(node.get_x()[1], x_array)
+    assert numpy.array_equal(node.get_y()[0][1], y_array)
+
+    loaded = load_node(node.uuid)
+    assert numpy.array_equal(loaded.get_x()[1], x_array)
+    assert numpy.array_equal(loaded.get_y()[0][1], y_array)
+
+
+def test_constructor():
+    """Test the various construction options."""
+    with pytest.raises(TypeError):
+        node = XyData(numpy.array([1, 2]))
+
+    node = XyData()
+
+    with pytest.raises(NotExistent):
+        node.get_x()
+
+    with pytest.raises(NotExistent):
+        node.get_y()
+
+    x_array = numpy.array([1, 2])
+    y_array = numpy.array([3, 4])
+    node = XyData(x_array, y_array, x_name='x_name', x_units='x_unit', y_names='y_name', y_units='y_units')
+    assert numpy.array_equal(node.get_x()[1], x_array)
+    assert numpy.array_equal(node.get_y()[0][1], y_array)