Merge pull request #7213 from saimn/fix-table-subclass

 Fix issue with serialization when using a Table subclass

CHANGES.rst

@@ -291,6 +291,8 @@ astropy.io.misc
 astropy.io.registry
 ^^^^^^^^^^^^^^^^^^^
 
+- Fix reading files with serialized metadata when using a Table subclass. [#7213]
+
 astropy.io.votable
 ^^^^^^^^^^^^^^^^^^
 

astropy/io/registry.py

@@ -517,18 +517,14 @@ def read(cls, *args, format=None, **kwargs):
         data = reader(*args, **kwargs)
 
         if not isinstance(data, cls):
-            if issubclass(cls, data.__class__):
-                # User has read with a subclass where only the parent class is
-                # registered.  This returns the parent class, so try coercing
-                # to desired subclass.
-                try:
-                    data = cls(data)
-                except Exception:
-                    raise TypeError('could not convert reader output to {0} '
-                                    'class.'.format(cls.__name__))
-            else:
-                raise TypeError("reader should return a {0} instance"
-                                "".format(cls.__name__))
+            # User has read with a subclass where only the parent class is
+            # registered.  This returns the parent class, so try coercing
+            # to desired subclass.
+            try:
+                data = cls(data)
+            except Exception:
+                raise TypeError('could not convert reader output to {0} '
+                                'class.'.format(cls.__name__))
     finally:
         if ctx is not None:
             ctx.__exit__(*sys.exc_info())

astropy/io/tests/test_registry.py

@@ -1,7 +1,5 @@
 # Licensed under a 3-clause BSD style license - see LICENSE.rst
 
-
-
 import os
 from copy import copy
 from io import StringIO
@@ -12,11 +10,18 @@
 from ..registry import _readers, _writers, _identifiers
 from .. import registry as io_registry
 from ...table import Table
+from ... import units as u
 
 _READERS_ORIGINAL = copy(_readers)
 _WRITERS_ORIGINAL = copy(_writers)
 _IDENTIFIERS_ORIGINAL = copy(_identifiers)
 
+try:
+    import yaml  # pylint: disable=W0611
+    HAS_YAML = True
+except ImportError:
+    HAS_YAML = False
+
 
 class TestData:
     read = classmethod(io_registry.read)
@@ -317,13 +322,6 @@ def test_read_valid_return():
     assert isinstance(t, TestData)
 
 
-def test_read_invalid_return():
-    io_registry.register_reader('test', TestData, lambda: 'spam')
-    with pytest.raises(TypeError) as exc:
-        TestData.read(format='test')
-    assert str(exc.value) == "reader should return a TestData instance"
-
-
 def test_non_existing_unknown_ext():
     """Raise the correct error when attempting to read a non-existing
     file with an unknown extension."""
@@ -410,3 +408,30 @@ class MyTable(Table):
         mt = MyTable([[1], [2]], names=['a', 'b'])
         mt.write(buffer, format='ascii')
         assert buffer.getvalue() == os.linesep.join(['a b', '1 2', ''])
+
+    def test_read_table_subclass_with_columns_attributes(self, tmpdir):
+        """Regression test for https://github.com/astropy/astropy/issues/7181
+        """
+
+        class MTable(Table):
+            pass
+
+        mt = MTable([[1, 2.5]], names=['a'])
+        mt['a'].unit = u.m
+        mt['a'].format = '.4f'
+        mt['a'].description = 'hello'
+
+        testfile = str(tmpdir.join('junk.fits'))
+        mt.write(testfile, overwrite=True)
+
+        t = MTable.read(testfile)
+        assert np.all(mt == t)
+        assert mt.colnames == t.colnames
+        assert type(t) is MTable
+        assert t['a'].unit == u.m
+        if HAS_YAML:
+            assert t['a'].format == '.4f'
+            assert t['a'].description == 'hello'
+        else:
+            assert t['a'].format is None
+            assert t['a'].description is None