recfunctions.append_fields fails on arrays containing objects (Trac #1751) #2346

class TestAppendFieldsObj(TestCase):
    """
    Test append_fields with arrays containing objects
    """
    def setUp(self):
        from datetime import date
        self.data = dict(obj=date(2000, 1, 1))

    def test_append_to_objects(self):
        "Test append_fields when the base array contains objects"
        obj = self.data['obj']
        x = np.array([(obj, 1.), (obj, 2.)], dtype=[('A', object), ('B', float)])
        y = np.array([10, 20], dtype=int)
        test = append_fields(x, 'C', data=y, usemask=False)
        control = np.array([(obj, 1.0, 10), (obj, 2.0, 20)],
                           dtype=[('A', object), ('B', float), ('C', int)])
        assert_equal(test, control)
    #
    def test_append_with_objects(self):
        "Test append_fields when the appended data contains objects"
        obj = self.data['obj']
        x = np.array([(10, 1.), (20, 2.)], dtype=[('A', int), ('B', float)])
        y = np.array([obj, obj], dtype=object)
        test = append_fields(y, 'C', data=y, dtypes=object, usemask=False)
        control = np.array([(10, 1.0, obj), (20, 2.0, obj)],
                           dtype=[('A', int), ('B', float), ('C', object)])
        assert_equal(test, control)






======================================================================
ERROR: Test append_fields when the base array contains objects
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Traceback (most recent call last):
  File "/home/kolpakov/lib/python2.6/site-packages/numpy/lib/tests/test_recfunctions.py", line 406, in test_append_to_objects
    test = append_fields(x, 'C', data=y, usemask=False)
  File "/home/kolpakov/lib/python2.6/site-packages/numpy/lib/recfunctions.py", line 629, in append_fields
    base = merge_arrays(base, usemask=usemask, fill_value=fill_value)
  File "/home/kolpakov/lib/python2.6/site-packages/numpy/lib/recfunctions.py", line 399, in merge_arrays
    return seqarrays.view(dtype=seqdtype, type=seqtype)
TypeError: Cannot change data-type for object array.

======================================================================
ERROR: Test append_fields when the appended data contains objects
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/kolpakov/lib/python2.6/site-packages/numpy/lib/tests/test_recfunctions.py", line 416, in test_append_with_objects
    test = append_fields(y, 'C', data=y, dtypes=object, usemask=False)
  File "/home/kolpakov/lib/python2.6/site-packages/numpy/lib/recfunctions.py", line 627, in append_fields
    for (a, n, d) in zip(data, names, dtypes)]
TypeError: Cannot change data-type for object array.

----------------------------------------------------------------------
Ran 33 tests in 0.062s

base = merge_arrays(base, usemask=usemask, fill_value=fill_value)