From e305456cc4d1331d8629b3a0b39019b2b29f481e Mon Sep 17 00:00:00 2001
From: System Administrator <root@aaryas-MacBook-Pro.local>
Date: Sat, 25 Mar 2017 13:41:17 +0530
Subject: [PATCH 01/12] preliminary fix for quantity columns to be written to
 fits

---
 astropy/table/table.py            |  5 ++---
 astropy/table/tests/test_mixin.py | 17 +++++++++--------
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/astropy/table/table.py b/astropy/table/table.py
index a029bcd5852..0e71cd647a4 100644
--- a/astropy/table/table.py
+++ b/astropy/table/table.py
@@ -852,10 +852,9 @@ def __bytes__(self):
     @property
     def has_mixin_columns(self):
         """
-        True if table has any mixin columns (defined as columns that are not Column
-        subclasses)
+        True if QTable has any mixin columns other than Quantity subclasses.
         """
-        return any(has_info_class(col, MixinInfo) for col in self.columns.values())
+        return any(not isinstance(col, (BaseColumn, Quantity)) for col in self.columns.values())
 
     def _add_as_mixin_column(self, col):
         """
diff --git a/astropy/table/tests/test_mixin.py b/astropy/table/tests/test_mixin.py
index 691d69549a1..bf59ec546f5 100644
--- a/astropy/table/tests/test_mixin.py
+++ b/astropy/table/tests/test_mixin.py
@@ -26,7 +26,7 @@
 from ... import units as u
 from .. import table_helpers
 from .conftest import MIXIN_COLS
-
+from ...units import Quantity
 
 def test_attributes(mixin_cols):
     """
@@ -110,13 +110,14 @@ def test_io_write_fail(mixin_cols):
     this just confirms no exceptions.
     """
     t = QTable(mixin_cols)
-    for fmt in ('fits', 'votable', 'hdf5'):
-        if fmt == 'hdf5' and not HAS_H5PY:
-            continue
-        out = StringIO()
-        with pytest.raises(ValueError) as err:
-            t.write(out, format=fmt)
-        assert 'cannot write table with mixin column(s)' in str(err.value)
+    if all(not isinstance(col, Quantity) for col in t.columns.values()):
+        for fmt in ('fits', 'votable', 'hdf5'):
+            if fmt == 'hdf5' and not HAS_H5PY:
+                continue
+            out = StringIO()
+            with pytest.raises(ValueError) as err:
+                t.write(out, format=fmt)
+            assert 'cannot write table with mixin column(s)' in str(err.value)
 
 
 def test_join(table_types):

From 9924a94486ccb28b7b1b4130cbe6961a37af5a9d Mon Sep 17 00:00:00 2001
From: System Administrator <root@aaryas-MacBook-Pro.local>
Date: Sun, 26 Mar 2017 12:53:59 +0530
Subject: [PATCH 02/12] Requested changes done and votable changes for Quantity
 columns

---
 CHANGES.rst                       |  2 +
 astropy/io/fits/convenience.py    | 15 ++++---
 astropy/io/misc/hdf5.py           | 14 ++++---
 astropy/io/votable/connect.py     | 15 ++++---
 astropy/io/votable/tree.py        | 65 +++++++++++++++++++------------
 astropy/table/table.py            | 18 ++++++++-
 astropy/table/tests/test_mixin.py | 42 +++++++++++++-------
 7 files changed, 114 insertions(+), 57 deletions(-)

diff --git a/CHANGES.rst b/CHANGES.rst
index 484050f1e52..9ef6dad0ffc 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -62,6 +62,8 @@ New Features
     the string gets truncated.  This can occur because numpy string
     arrays are fixed-width and silently drop characters which do not
     fit within the fixed width. [#5624]
+  - Added functionality to allow ``astropy.units.Quantity`` to be written 
+    as a normal column to FITS, hdf5, and votable files. [#5910]
 
 - ``astropy.time``
 
diff --git a/astropy/io/fits/convenience.py b/astropy/io/fits/convenience.py
index b538cc6aeb7..b773f88e132 100644
--- a/astropy/io/fits/convenience.py
+++ b/astropy/io/fits/convenience.py
@@ -72,11 +72,12 @@
 from .fitsrec import FITS_rec
 from ...units import Unit
 from ...units.format.fits import UnitScaleError
+from ...units import Quantity
 from ...extern import six
 from ...extern.six import string_types
 from ...utils.exceptions import AstropyUserWarning
 from ...utils.decorators import deprecated_renamed_argument
-
+from ...table.column import BaseColumn
 
 __all__ = ['getheader', 'getdata', 'getval', 'setval', 'delval', 'writeto',
            'append', 'update', 'info', 'tabledump', 'tableload',
@@ -460,12 +461,14 @@ def table_to_hdu(table):
     # Avoid circular imports
     from .connect import is_column_keyword, REMOVE_KEYWORDS
 
-    # Tables with mixin columns are not supported
+    # Not all tables with mixin columns are supported
     if table.has_mixin_columns:
-        mixin_names = [name for name, col in table.columns.items()
-                       if not isinstance(col, table.ColumnClass)]
-        raise ValueError('cannot write table with mixin column(s) {0}'
-                         .format(mixin_names))
+        # Only those columns which are instances of BaseColumn or Quantity can be written
+        unsupported_cols = table.columns.not_isinstance(BaseColumn, Quantity)
+        if unsupported_cols:
+            unsupported_names = [col.info.name for col in unsupported_cols]
+            raise ValueError('cannot write table with mixin column(s) {0}'
+                         .format(unsupported_names))
 
     # Create a new HDU object
     if table.masked:
diff --git a/astropy/io/misc/hdf5.py b/astropy/io/misc/hdf5.py
index 80831950642..10f48c24710 100644
--- a/astropy/io/misc/hdf5.py
+++ b/astropy/io/misc/hdf5.py
@@ -15,6 +15,8 @@
 from ...utils.exceptions import AstropyUserWarning
 from ...extern import six
 from ...table import meta
+from ...units import Quantity
+from ...table.column import BaseColumn
 
 HDF5_SIGNATURE = b'\x89HDF\r\n\x1a\n'
 META_KEY = '__table_column_meta__'
@@ -194,12 +196,14 @@ def write_table_hdf5(table, output, path=None, compression=False,
     except ImportError:
         raise Exception("h5py is required to read and write HDF5 files")
 
-    # Tables with mixin columns are not supported
+    # Not all tables with mixin columns are supported
     if table.has_mixin_columns:
-        mixin_names = [name for name, col in table.columns.items()
-                       if not isinstance(col, table.ColumnClass)]
-        raise ValueError('cannot write table with mixin column(s) {0} to HDF5'
-                         .format(mixin_names))
+        # Only those columns which are instances of BaseColumn or Quantity can be written
+        unsupported_cols = table.columns.not_isinstance(BaseColumn, Quantity)
+        if unsupported_cols:
+            unsupported_names = [col.info.name for col in unsupported_cols]
+            raise ValueError('cannot write table with mixin column(s) {0} to HDF5'
+                         .format(unsupported_names))
 
     if path is None:
         raise ValueError("table path should be set via the path= argument")
diff --git a/astropy/io/votable/connect.py b/astropy/io/votable/connect.py
index 633cd572e31..a42eaeca022 100644
--- a/astropy/io/votable/connect.py
+++ b/astropy/io/votable/connect.py
@@ -10,7 +10,8 @@
 from .tree import VOTableFile, Table as VOTable
 from .. import registry as io_registry
 from ...table import Table
-
+from ...table.column import BaseColumn
+from ...units import Quantity
 
 def is_votable(origin, filepath, fileobj, *args, **kwargs):
     """
@@ -139,12 +140,14 @@ def write_table_votable(input, output, table_id=None, overwrite=False,
         ``tabledata``.  See :ref:`votable-serialization`.
     """
 
-    # Tables with mixin columns are not supported
+    # Not all tables with mixin columns are supported
     if input.has_mixin_columns:
-        mixin_names = [name for name, col in input.columns.items()
-                       if not isinstance(col, input.ColumnClass)]
-        raise ValueError('cannot write table with mixin column(s) {0} to VOTable'
-                         .format(mixin_names))
+        # Only those columns which are instances of BaseColumn or Quantity can be written
+        unsupported_cols = input.columns.not_isinstance(BaseColumn, Quantity)
+        if unsupported_cols:
+            unsupported_names = [col.info.name for col in unsupported_cols]
+            raise ValueError('cannot write table with mixin column(s) {0} to VOTable'
+                         .format(unsupported_names))
 
     # Check if output file already exists
     if isinstance(output, six.string_types) and os.path.exists(output):
diff --git a/astropy/io/votable/tree.py b/astropy/io/votable/tree.py
index 7183f03ff0a..63e81d509a8 100644
--- a/astropy/io/votable/tree.py
+++ b/astropy/io/votable/tree.py
@@ -25,7 +25,7 @@
 from ...utils.xml.writer import XMLWriter
 from ...utils.exceptions import AstropyDeprecationWarning
 from ...utils.misc import InheritDocstrings
-
+from ...units import Quantity
 from . import converters
 from .exceptions import (warn_or_raise, vo_warn, vo_raise, vo_reraise,
                          warn_unknown_attrs, W06, W07, W08, W09, W10, W11, W12,
@@ -1115,22 +1115,25 @@ def to_table_column(self, column):
         column.meta['values'] = meta
 
     def from_table_column(self, column):
-        if 'values' not in column.meta:
-            return
-
-        meta = column.meta['values']
-        for key in ['ID', 'null']:
-            val = meta.get(key, None)
-            if val is not None:
-                setattr(self, key, val)
-        if 'min' in meta:
-            self.min = meta['min']['value']
-            self.min_inclusive = meta['min']['inclusive']
-        if 'max' in meta:
-            self.max = meta['max']['value']
-            self.max_inclusive = meta['max']['inclusive']
-        if 'options' in meta:
-            self._options = list(meta['options'].items())
+        if isinstance(column, Quantity):
+            column = column.info
+        if column.meta is not None:
+            if 'values' not in column.meta:
+                return
+
+            meta = column.meta['values']
+            for key in ['ID', 'null']:
+                val = meta.get(key, None)
+                if val is not None:
+                    setattr(self, key, val)
+            if 'min' in meta:
+                self.min = meta['min']['value']
+                self.min_inclusive = meta['min']['inclusive']
+            if 'max' in meta:
+                self.max = meta['max']['value']
+                self.max_inclusive = meta['max']['inclusive']
+            if 'options' in meta:
+                self._options = list(meta['options'].items())
 
 
 class Field(SimpleElement, _IDProperty, _NameProperty, _XtypeProperty,
@@ -1546,26 +1549,38 @@ def from_table_column(cls, votable, column):
         Restores a `Field` instance from a given
         `astropy.table.Column` instance.
         """
+        Q_column = None
+        if isinstance(column, Quantity):
+            Q_column = column
+            column = column.info
         kwargs = {}
         for key in ['ucd', 'width', 'precision', 'utype', 'xtype']:
-            val = column.meta.get(key, None)
-            if val is not None:
-                kwargs[key] = val
+            if column.meta is not None:
+                val = column.meta.get(key, None)
+                if val is not None:
+                    kwargs[key] = val
         # TODO: Use the unit framework when available
         if column.unit is not None:
             kwargs['unit'] = column.unit
         kwargs['name'] = column.name
-        result = converters.table_column_to_votable_datatype(column)
+        if Q_column is not None:
+            result = converters.table_column_to_votable_datatype(Q_column)
+        else:
+            result = converters.table_column_to_votable_datatype(column)
         kwargs.update(result)
 
         field = cls(votable, **kwargs)
 
         if column.description is not None:
             field.description = column.description
-        field.values.from_table_column(column)
-        if 'links' in column.meta:
-            for link in column.meta['links']:
-                field.links.append(Link.from_table_column(link))
+        if Q_column is not None:
+            field.values.from_table_column(Q_column)
+        else:
+            field.values.from_table_column(column)
+        if column.meta is not None:
+            if 'links' in column.meta:
+                for link in column.meta['links']:
+                    field.links.append(Link.from_table_column(link))
 
         # TODO: Parse format into precision and width
         return field
diff --git a/astropy/table/table.py b/astropy/table/table.py
index 0e71cd647a4..f170b1d0474 100644
--- a/astropy/table/table.py
+++ b/astropy/table/table.py
@@ -150,6 +150,19 @@ def keys(self):
     def values(self):
         return list(OrderedDict.values(self))
 
+    def isinstance(self, *cls):
+        '''
+        Return a list of columns which are instances of the specified classes.
+        '''
+        cols = [col for col in self.values() if isinstance(col, cls)]
+        return cols
+
+    def not_isinstance(self, *cls):
+        '''
+        Return a list of columns which are not instances of the specified classes.
+        '''
+        cols = [col for col in self.values() if not isinstance(col, cls)]
+        return cols
 
 class Table(object):
     """A class to represent tables of heterogeneous data.
@@ -852,9 +865,10 @@ def __bytes__(self):
     @property
     def has_mixin_columns(self):
         """
-        True if QTable has any mixin columns other than Quantity subclasses.
+        True if table has any mixin columns (defined as columns that are not Column
+        subclasses)        
         """
-        return any(not isinstance(col, (BaseColumn, Quantity)) for col in self.columns.values())
+        return any(has_info_class(col, MixinInfo) for col in self.columns.values())
 
     def _add_as_mixin_column(self, col):
         """
diff --git a/astropy/table/tests/test_mixin.py b/astropy/table/tests/test_mixin.py
index bf59ec546f5..bc2f5952914 100644
--- a/astropy/table/tests/test_mixin.py
+++ b/astropy/table/tests/test_mixin.py
@@ -27,6 +27,7 @@
 from .. import table_helpers
 from .conftest import MIXIN_COLS
 from ...units import Quantity
+from ..column import BaseColumn
 
 def test_attributes(mixin_cols):
     """
@@ -100,24 +101,39 @@ def test_io_ascii_write():
         if fmt['Write'] and '.fast_' not in fmt['Format']:
             out = StringIO()
             t.write(out, format=fmt['Format'])
-
+            
+def test_io_Quantity_write():
+    """
+    Test that table with Quantity mixin column can be written by io.votable,
+    io.fits, and io.misc.hdf5. No validation of the output is done,
+    this just confirms no exceptions.
+    """
+    t = QTable()
+    t['a'] = Quantity([1,2,4], unit='Angstrom')
+    for fmt in ('fits', 'votable', 'hdf5'):
+        if fmt == 'hdf5' and not HAS_H5PY:
+            continue
+        out = StringIO()
+        t.write(out, format=fmt)
 
 def test_io_write_fail(mixin_cols):
     """
-    Test that table with mixin column cannot be written by io.votable,
-    io.fits, and io.misc.hdf5
-    every pure Python writer.  No validation of the output is done,
-    this just confirms no exceptions.
+    Test that table with mixin column (excluding Quantity) cannot be written by io.votable,
+    io.fits, and io.misc.hdf5.
     """
     t = QTable(mixin_cols)
-    if all(not isinstance(col, Quantity) for col in t.columns.values()):
-        for fmt in ('fits', 'votable', 'hdf5'):
-            if fmt == 'hdf5' and not HAS_H5PY:
-                continue
-            out = StringIO()
-            with pytest.raises(ValueError) as err:
-                t.write(out, format=fmt)
-            assert 'cannot write table with mixin column(s)' in str(err.value)
+    #Only do this test if there are unsupported column types (i.e. anything besides
+    #BaseColumn or Quantity subclasses.
+    unsupported_cols = t.columns.not_isinstance(BaseColumn, Quantity)
+    if not unsupported_cols:
+        pytest.skip("no unsupported column types")
+    for fmt in ('fits', 'votable', 'hdf5'):
+        if fmt == 'hdf5' and not HAS_H5PY:
+            continue
+        out = StringIO()
+        with pytest.raises(ValueError) as err:
+            t.write(out, format=fmt)
+        assert 'cannot write table with mixin column(s)' in str(err.value)
 
 
 def test_join(table_types):

From 1e9e9fe47927ca76db01ace27fc0764ef1bce562 Mon Sep 17 00:00:00 2001
From: System Administrator <root@aaryas-MacBook-Pro.local>
Date: Mon, 27 Mar 2017 19:49:26 +0530
Subject: [PATCH 03/12] Changes requested

---
 astropy/io/fits/convenience.py    |  3 +-
 astropy/io/votable/tree.py        | 72 +++++++++++++------------------
 astropy/table/table.py            | 30 ++++++++++---
 astropy/table/tests/test_mixin.py |  8 +++-
 4 files changed, 63 insertions(+), 50 deletions(-)

diff --git a/astropy/io/fits/convenience.py b/astropy/io/fits/convenience.py
index b773f88e132..929d6e44835 100644
--- a/astropy/io/fits/convenience.py
+++ b/astropy/io/fits/convenience.py
@@ -77,7 +77,6 @@
 from ...extern.six import string_types
 from ...utils.exceptions import AstropyUserWarning
 from ...utils.decorators import deprecated_renamed_argument
-from ...table.column import BaseColumn
 
 __all__ = ['getheader', 'getdata', 'getval', 'setval', 'delval', 'writeto',
            'append', 'update', 'info', 'tabledump', 'tableload',
@@ -463,6 +462,8 @@ def table_to_hdu(table):
 
     # Not all tables with mixin columns are supported
     if table.has_mixin_columns:
+        from ...table.column import BaseColumn
+
         # Only those columns which are instances of BaseColumn or Quantity can be written
         unsupported_cols = table.columns.not_isinstance(BaseColumn, Quantity)
         if unsupported_cols:
diff --git a/astropy/io/votable/tree.py b/astropy/io/votable/tree.py
index 63e81d509a8..e166e6fd7ef 100644
--- a/astropy/io/votable/tree.py
+++ b/astropy/io/votable/tree.py
@@ -1115,25 +1115,22 @@ def to_table_column(self, column):
         column.meta['values'] = meta
 
     def from_table_column(self, column):
-        if isinstance(column, Quantity):
-            column = column.info
-        if column.meta is not None:
-            if 'values' not in column.meta:
-                return
-
-            meta = column.meta['values']
-            for key in ['ID', 'null']:
-                val = meta.get(key, None)
-                if val is not None:
-                    setattr(self, key, val)
-            if 'min' in meta:
-                self.min = meta['min']['value']
-                self.min_inclusive = meta['min']['inclusive']
-            if 'max' in meta:
-                self.max = meta['max']['value']
-                self.max_inclusive = meta['max']['inclusive']
-            if 'options' in meta:
-                self._options = list(meta['options'].items())
+        if column.info.meta is None or 'values' not in column.info.meta:
+            return
+
+        meta = column.info.meta['values']
+        for key in ['ID', 'null']:
+            val = meta.get(key, None)
+            if val is not None:
+                setattr(self, key, val)
+        if 'min' in meta:
+            self.min = meta['min']['value']
+            self.min_inclusive = meta['min']['inclusive']
+        if 'max' in meta:
+            self.max = meta['max']['value']
+            self.max_inclusive = meta['max']['inclusive']
+        if 'options' in meta:
+            self._options = list(meta['options'].items())
 
 
 class Field(SimpleElement, _IDProperty, _NameProperty, _XtypeProperty,
@@ -1549,37 +1546,26 @@ def from_table_column(cls, votable, column):
         Restores a `Field` instance from a given
         `astropy.table.Column` instance.
         """
-        Q_column = None
-        if isinstance(column, Quantity):
-            Q_column = column
-            column = column.info
         kwargs = {}
+        meta = column.info.meta or {}
         for key in ['ucd', 'width', 'precision', 'utype', 'xtype']:
-            if column.meta is not None:
-                val = column.meta.get(key, None)
-                if val is not None:
-                    kwargs[key] = val
+            val = meta.get(key, None)
+            if val is not None:
+                kwargs[key] = val
         # TODO: Use the unit framework when available
-        if column.unit is not None:
-            kwargs['unit'] = column.unit
-        kwargs['name'] = column.name
-        if Q_column is not None:
-            result = converters.table_column_to_votable_datatype(Q_column)
-        else:
-            result = converters.table_column_to_votable_datatype(column)
+        if column.info.unit is not None:
+            kwargs['unit'] = column.info.unit
+        kwargs['name'] = column.info.name
+        result = converters.table_column_to_votable_datatype(column)
         kwargs.update(result)
 
         field = cls(votable, **kwargs)
 
-        if column.description is not None:
-            field.description = column.description
-        if Q_column is not None:
-            field.values.from_table_column(Q_column)
-        else:
-            field.values.from_table_column(column)
-        if column.meta is not None:
-            if 'links' in column.meta:
-                for link in column.meta['links']:
+        if column.info.description is not None:
+            field.description = column.info.description
+        field.values.from_table_column(column)
+        if 'links' in meta:
+            for link in meta['links']:
                     field.links.append(Link.from_table_column(link))
 
         # TODO: Parse format into precision and width
diff --git a/astropy/table/table.py b/astropy/table/table.py
index f170b1d0474..1263b63b25c 100644
--- a/astropy/table/table.py
+++ b/astropy/table/table.py
@@ -151,16 +151,36 @@ def values(self):
         return list(OrderedDict.values(self))
 
     def isinstance(self, *cls):
-        '''
+        """
         Return a list of columns which are instances of the specified classes.
-        '''
+
+        Parameters
+        ----------
+        *cls : argument list of Column classes
+            List of Column (including mixin) classes.
+
+        Returns
+        -------
+        col_list : list of Columns
+            List of Column objects which are instances of given classes.
+        """
         cols = [col for col in self.values() if isinstance(col, cls)]
         return cols
 
     def not_isinstance(self, *cls):
-        '''
+        """
         Return a list of columns which are not instances of the specified classes.
-        '''
+
+        Parameters
+        ----------
+        *cls : argument list of Column classes
+            List of Column (including mixin) classes.
+
+        Returns
+        -------
+        col_list : list of Columns
+            List of Column objects which are not instances of given classes.
+        """
         cols = [col for col in self.values() if not isinstance(col, cls)]
         return cols
 
@@ -866,7 +886,7 @@ def __bytes__(self):
     def has_mixin_columns(self):
         """
         True if table has any mixin columns (defined as columns that are not Column
-        subclasses)        
+        subclasses).
         """
         return any(has_info_class(col, MixinInfo) for col in self.columns.values())
 
diff --git a/astropy/table/tests/test_mixin.py b/astropy/table/tests/test_mixin.py
index bc2f5952914..3a43962f8f4 100644
--- a/astropy/table/tests/test_mixin.py
+++ b/astropy/table/tests/test_mixin.py
@@ -29,6 +29,7 @@
 from ...units import Quantity
 from ..column import BaseColumn
 
+
 def test_attributes(mixin_cols):
     """
     Required attributes for a column can be set.
@@ -101,7 +102,8 @@ def test_io_ascii_write():
         if fmt['Write'] and '.fast_' not in fmt['Format']:
             out = StringIO()
             t.write(out, format=fmt['Format'])
-            
+
+
 def test_io_Quantity_write():
     """
     Test that table with Quantity mixin column can be written by io.votable,
@@ -114,8 +116,12 @@ def test_io_Quantity_write():
         if fmt == 'hdf5' and not HAS_H5PY:
             continue
         out = StringIO()
+        if fmt == 'hdf5':
+            t.write(out, format=fmt, path='data')
+            continue
         t.write(out, format=fmt)
 
+
 def test_io_write_fail(mixin_cols):
     """
     Test that table with mixin column (excluding Quantity) cannot be written by io.votable,

From b161978cb9bd71939916eb37a46d7885e88f06ea Mon Sep 17 00:00:00 2001
From: System Administrator <root@aaryas-MacBook-Pro.local>
Date: Mon, 27 Mar 2017 19:56:30 +0530
Subject: [PATCH 04/12] Few changes

---
 CHANGES.rst | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGES.rst b/CHANGES.rst
index 9ef6dad0ffc..a596601529b 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -63,7 +63,7 @@ New Features
     arrays are fixed-width and silently drop characters which do not
     fit within the fixed width. [#5624]
   - Added functionality to allow ``astropy.units.Quantity`` to be written 
-    as a normal column to FITS, hdf5, and votable files. [#5910]
+    as a normal column to FITS, HDF5, and votable files. [#5910]
 
 - ``astropy.time``
 

From e307ad4cc0a88fe6d12481be1b4010f7ca989a92 Mon Sep 17 00:00:00 2001
From: System Administrator <root@aaryas-MacBook-Pro.local>
Date: Mon, 27 Mar 2017 20:03:23 +0530
Subject: [PATCH 05/12] Indentation fix

---
 astropy/io/fits/convenience.py | 1 +
 astropy/io/votable/tree.py     | 2 +-
 2 files changed, 2 insertions(+), 1 deletion(-)

diff --git a/astropy/io/fits/convenience.py b/astropy/io/fits/convenience.py
index 929d6e44835..2052b4003e7 100644
--- a/astropy/io/fits/convenience.py
+++ b/astropy/io/fits/convenience.py
@@ -78,6 +78,7 @@
 from ...utils.exceptions import AstropyUserWarning
 from ...utils.decorators import deprecated_renamed_argument
 
+
 __all__ = ['getheader', 'getdata', 'getval', 'setval', 'delval', 'writeto',
            'append', 'update', 'info', 'tabledump', 'tableload',
            'table_to_hdu', 'printdiff']
diff --git a/astropy/io/votable/tree.py b/astropy/io/votable/tree.py
index e166e6fd7ef..6253a4f2e86 100644
--- a/astropy/io/votable/tree.py
+++ b/astropy/io/votable/tree.py
@@ -1566,7 +1566,7 @@ def from_table_column(cls, votable, column):
         field.values.from_table_column(column)
         if 'links' in meta:
             for link in meta['links']:
-                    field.links.append(Link.from_table_column(link))
+                field.links.append(Link.from_table_column(link))
 
         # TODO: Parse format into precision and width
         return field

From 38cda35bd248818e2666bc83d8601b90b4753b2f Mon Sep 17 00:00:00 2001
From: System Administrator <root@aaryas-MacBook-Pro.local>
Date: Mon, 27 Mar 2017 20:07:29 +0530
Subject: [PATCH 06/12] Circular import comment

---
 astropy/io/fits/convenience.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/astropy/io/fits/convenience.py b/astropy/io/fits/convenience.py
index 2052b4003e7..21287d0fb96 100644
--- a/astropy/io/fits/convenience.py
+++ b/astropy/io/fits/convenience.py
@@ -463,6 +463,7 @@ def table_to_hdu(table):
 
     # Not all tables with mixin columns are supported
     if table.has_mixin_columns:
+        #the import is done here, in order to avoid a circular import
         from ...table.column import BaseColumn
 
         # Only those columns which are instances of BaseColumn or Quantity can be written

From d4804399061784c5fe14aaf639650e7cfc29a61c Mon Sep 17 00:00:00 2001
From: System Administrator <root@aaryas-MacBook-Pro.local>
Date: Tue, 28 Mar 2017 10:53:00 +0530
Subject: [PATCH 07/12] Test Changes and Import comment

---
 astropy/io/fits/convenience.py    |  2 +-
 astropy/table/tests/test_mixin.py | 12 +++++++++---
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/astropy/io/fits/convenience.py b/astropy/io/fits/convenience.py
index 21287d0fb96..ddd8b1fe197 100644
--- a/astropy/io/fits/convenience.py
+++ b/astropy/io/fits/convenience.py
@@ -463,7 +463,7 @@ def table_to_hdu(table):
 
     # Not all tables with mixin columns are supported
     if table.has_mixin_columns:
-        #the import is done here, in order to avoid a circular import
+        #the import is done here, in order to avoid it at build time as erfa is not yet available then
         from ...table.column import BaseColumn
 
         # Only those columns which are instances of BaseColumn or Quantity can be written
diff --git a/astropy/table/tests/test_mixin.py b/astropy/table/tests/test_mixin.py
index 3a43962f8f4..db82ef90940 100644
--- a/astropy/table/tests/test_mixin.py
+++ b/astropy/table/tests/test_mixin.py
@@ -104,7 +104,7 @@ def test_io_ascii_write():
             t.write(out, format=fmt['Format'])
 
 
-def test_io_Quantity_write():
+def test_io_Quantity_write(tmpdir):
     """
     Test that table with Quantity mixin column can be written by io.votable,
     io.fits, and io.misc.hdf5. No validation of the output is done,
@@ -112,14 +112,20 @@ def test_io_Quantity_write():
     """
     t = QTable()
     t['a'] = Quantity([1,2,4], unit='Angstrom')
+    
+    filename = tmpdir.join("table-tmp").strpath
+    open(filename, 'w').close()
+    
     for fmt in ('fits', 'votable', 'hdf5'):
         if fmt == 'hdf5' and not HAS_H5PY:
             continue
         out = StringIO()
         if fmt == 'hdf5':
-            t.write(out, format=fmt, path='data')
+            t.write(filename, format=fmt, path='data', overwrite=True)
             continue
-        t.write(out, format=fmt)
+        t.write(filename, format=fmt, overwrite=True)
+        if fmt == 'fits':
+            assert QTable.read(filename, format=fmt)['a'].unit == 'Angstrom'
 
 
 def test_io_write_fail(mixin_cols):

From 3a7af1e0a93797e48ca9d07a704e1bc3247a6d71 Mon Sep 17 00:00:00 2001
From: System Administrator <root@aaryas-MacBook-Pro.local>
Date: Tue, 28 Mar 2017 12:39:53 +0530
Subject: [PATCH 08/12] remove whitespace

---
 astropy/table/tests/test_mixin.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/astropy/table/tests/test_mixin.py b/astropy/table/tests/test_mixin.py
index db82ef90940..eb8b9386bae 100644
--- a/astropy/table/tests/test_mixin.py
+++ b/astropy/table/tests/test_mixin.py
@@ -112,10 +112,10 @@ def test_io_Quantity_write(tmpdir):
     """
     t = QTable()
     t['a'] = Quantity([1,2,4], unit='Angstrom')
-    
+
     filename = tmpdir.join("table-tmp").strpath
     open(filename, 'w').close()
-    
+
     for fmt in ('fits', 'votable', 'hdf5'):
         if fmt == 'hdf5' and not HAS_H5PY:
             continue

From fda7b16172f3866aa8b970947e4b29dfd088e935 Mon Sep 17 00:00:00 2001
From: AustereCuriosity <aaryapatil1996@gmail.com>
Date: Wed, 19 Apr 2017 23:27:37 +0530
Subject: [PATCH 09/12] Minor changes

---
 CHANGES.rst                | 1 +
 astropy/io/votable/tree.py | 1 -
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/CHANGES.rst b/CHANGES.rst
index a596601529b..1deb57784e9 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -62,6 +62,7 @@ New Features
     the string gets truncated.  This can occur because numpy string
     arrays are fixed-width and silently drop characters which do not
     fit within the fixed width. [#5624]
+
   - Added functionality to allow ``astropy.units.Quantity`` to be written 
     as a normal column to FITS, HDF5, and votable files. [#5910]
 
diff --git a/astropy/io/votable/tree.py b/astropy/io/votable/tree.py
index 6253a4f2e86..d6546f1b4a4 100644
--- a/astropy/io/votable/tree.py
+++ b/astropy/io/votable/tree.py
@@ -25,7 +25,6 @@
 from ...utils.xml.writer import XMLWriter
 from ...utils.exceptions import AstropyDeprecationWarning
 from ...utils.misc import InheritDocstrings
-from ...units import Quantity
 from . import converters
 from .exceptions import (warn_or_raise, vo_warn, vo_raise, vo_reraise,
                          warn_unknown_attrs, W06, W07, W08, W09, W10, W11, W12,

From 0fd7c063d6d0b1eecfcaeac62182e46be9e16742 Mon Sep 17 00:00:00 2001
From: AustereCuriosity <aaryapatil1996@gmail.com>
Date: Thu, 20 Apr 2017 00:52:08 +0530
Subject: [PATCH 10/12] Added tests and a few changes

---
 astropy/io/fits/tests/test_connect.py |  7 ++++---
 astropy/io/votable/tree.py            |  1 +
 astropy/table/tests/test_mixin.py     | 13 +++++++------
 3 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/astropy/io/fits/tests/test_connect.py b/astropy/io/fits/tests/test_connect.py
index 8cf78f6d670..3100d0f36b0 100644
--- a/astropy/io/fits/tests/test_connect.py
+++ b/astropy/io/fits/tests/test_connect.py
@@ -92,13 +92,14 @@ def test_simple_noextension(self, tmpdir):
         t2 = Table.read(filename)
         assert equal_data(t1, t2)
 
-    def test_with_units(self, tmpdir):
+    @pytest.mark.parametrize('table_type', (Table, QTable))
+    def test_with_units(self, table_type, tmpdir):
         filename = str(tmpdir.join('test_with_units.fits'))
-        t1 = Table(self.data)
+        t1 = table_type(self.data)
         t1['a'].unit = u.m
         t1['c'].unit = u.km / u.s
         t1.write(filename, overwrite=True)
-        t2 = Table.read(filename)
+        t2 = table_type.read(filename)
         assert equal_data(t1, t2)
         assert t2['a'].unit == u.m
         assert t2['c'].unit == u.km / u.s
diff --git a/astropy/io/votable/tree.py b/astropy/io/votable/tree.py
index d6546f1b4a4..46bb6835317 100644
--- a/astropy/io/votable/tree.py
+++ b/astropy/io/votable/tree.py
@@ -25,6 +25,7 @@
 from ...utils.xml.writer import XMLWriter
 from ...utils.exceptions import AstropyDeprecationWarning
 from ...utils.misc import InheritDocstrings
+
 from . import converters
 from .exceptions import (warn_or_raise, vo_warn, vo_raise, vo_reraise,
                          warn_unknown_attrs, W06, W07, W08, W09, W10, W11, W12,
diff --git a/astropy/table/tests/test_mixin.py b/astropy/table/tests/test_mixin.py
index eb8b9386bae..913492d7ccc 100644
--- a/astropy/table/tests/test_mixin.py
+++ b/astropy/table/tests/test_mixin.py
@@ -24,10 +24,9 @@
 from ... import time
 from ... import coordinates
 from ... import units as u
+from ..column import BaseColumn
 from .. import table_helpers
 from .conftest import MIXIN_COLS
-from ...units import Quantity
-from ..column import BaseColumn
 
 
 def test_attributes(mixin_cols):
@@ -104,14 +103,14 @@ def test_io_ascii_write():
             t.write(out, format=fmt['Format'])
 
 
-def test_io_Quantity_write(tmpdir):
+def test_io_quantity_write(tmpdir):
     """
     Test that table with Quantity mixin column can be written by io.votable,
     io.fits, and io.misc.hdf5. No validation of the output is done,
     this just confirms no exceptions.
     """
     t = QTable()
-    t['a'] = Quantity([1,2,4], unit='Angstrom')
+    t['a'] = u.Quantity([1,2,4], unit='Angstrom')
 
     filename = tmpdir.join("table-tmp").strpath
     open(filename, 'w').close()
@@ -125,7 +124,9 @@ def test_io_Quantity_write(tmpdir):
             continue
         t.write(filename, format=fmt, overwrite=True)
         if fmt == 'fits':
-            assert QTable.read(filename, format=fmt)['a'].unit == 'Angstrom'
+            qt = QTable.read(filename, format=fmt)
+            assert isinstance(qt['a'], u.Quantity)
+            assert qt['a'].unit == 'Angstrom'
 
 
 def test_io_write_fail(mixin_cols):
@@ -136,7 +137,7 @@ def test_io_write_fail(mixin_cols):
     t = QTable(mixin_cols)
     #Only do this test if there are unsupported column types (i.e. anything besides
     #BaseColumn or Quantity subclasses.
-    unsupported_cols = t.columns.not_isinstance(BaseColumn, Quantity)
+    unsupported_cols = t.columns.not_isinstance(BaseColumn, u.Quantity)
     if not unsupported_cols:
         pytest.skip("no unsupported column types")
     for fmt in ('fits', 'votable', 'hdf5'):

From f7b42a964d51302b50cb25d1e1735705671b543a Mon Sep 17 00:00:00 2001
From: AustereCuriosity <aaryapatil1996@gmail.com>
Date: Thu, 20 Apr 2017 01:10:19 +0530
Subject: [PATCH 11/12] Minor error

---
 astropy/io/fits/tests/test_connect.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/astropy/io/fits/tests/test_connect.py b/astropy/io/fits/tests/test_connect.py
index 3100d0f36b0..c808b6f63b3 100644
--- a/astropy/io/fits/tests/test_connect.py
+++ b/astropy/io/fits/tests/test_connect.py
@@ -10,7 +10,7 @@
 
 from .... import units as u
 from ....extern.six.moves import range, zip
-from ....table import Table
+from ....table import Table, QTable
 from ....tests.helper import pytest, catch_warnings
 from ....units.format.fits import UnitScaleError
 

From 9d914372300d8bda4c7426fe2bfdbfc74c9ee063 Mon Sep 17 00:00:00 2001
From: AustereCuriosity <aaryapatil1996@gmail.com>
Date: Fri, 21 Apr 2017 20:15:08 +0530
Subject: [PATCH 12/12] Remove all changes for votable and HDF5

---
 CHANGES.rst                       |  2 +-
 astropy/io/fits/convenience.py    |  2 +-
 astropy/io/misc/hdf5.py           | 14 +++++---------
 astropy/io/votable/connect.py     | 15 ++++++---------
 astropy/io/votable/tree.py        | 21 ++++++++++-----------
 astropy/table/table.py            | 12 ++++++------
 astropy/table/tests/test_mixin.py | 23 ++++++++++++-----------
 7 files changed, 41 insertions(+), 48 deletions(-)

diff --git a/CHANGES.rst b/CHANGES.rst
index 1deb57784e9..c8f04911e73 100644
--- a/CHANGES.rst
+++ b/CHANGES.rst
@@ -64,7 +64,7 @@ New Features
     fit within the fixed width. [#5624]
 
   - Added functionality to allow ``astropy.units.Quantity`` to be written 
-    as a normal column to FITS, HDF5, and votable files. [#5910]
+    as a normal column to FITS files. [#5910]
 
 - ``astropy.time``
 
diff --git a/astropy/io/fits/convenience.py b/astropy/io/fits/convenience.py
index ddd8b1fe197..a59d7e4b2e0 100644
--- a/astropy/io/fits/convenience.py
+++ b/astropy/io/fits/convenience.py
@@ -467,7 +467,7 @@ def table_to_hdu(table):
         from ...table.column import BaseColumn
 
         # Only those columns which are instances of BaseColumn or Quantity can be written
-        unsupported_cols = table.columns.not_isinstance(BaseColumn, Quantity)
+        unsupported_cols = table.columns.not_isinstance((BaseColumn, Quantity))
         if unsupported_cols:
             unsupported_names = [col.info.name for col in unsupported_cols]
             raise ValueError('cannot write table with mixin column(s) {0}'
diff --git a/astropy/io/misc/hdf5.py b/astropy/io/misc/hdf5.py
index 10f48c24710..80831950642 100644
--- a/astropy/io/misc/hdf5.py
+++ b/astropy/io/misc/hdf5.py
@@ -15,8 +15,6 @@
 from ...utils.exceptions import AstropyUserWarning
 from ...extern import six
 from ...table import meta
-from ...units import Quantity
-from ...table.column import BaseColumn
 
 HDF5_SIGNATURE = b'\x89HDF\r\n\x1a\n'
 META_KEY = '__table_column_meta__'
@@ -196,14 +194,12 @@ def write_table_hdf5(table, output, path=None, compression=False,
     except ImportError:
         raise Exception("h5py is required to read and write HDF5 files")
 
-    # Not all tables with mixin columns are supported
+    # Tables with mixin columns are not supported
     if table.has_mixin_columns:
-        # Only those columns which are instances of BaseColumn or Quantity can be written
-        unsupported_cols = table.columns.not_isinstance(BaseColumn, Quantity)
-        if unsupported_cols:
-            unsupported_names = [col.info.name for col in unsupported_cols]
-            raise ValueError('cannot write table with mixin column(s) {0} to HDF5'
-                         .format(unsupported_names))
+        mixin_names = [name for name, col in table.columns.items()
+                       if not isinstance(col, table.ColumnClass)]
+        raise ValueError('cannot write table with mixin column(s) {0} to HDF5'
+                         .format(mixin_names))
 
     if path is None:
         raise ValueError("table path should be set via the path= argument")
diff --git a/astropy/io/votable/connect.py b/astropy/io/votable/connect.py
index a42eaeca022..633cd572e31 100644
--- a/astropy/io/votable/connect.py
+++ b/astropy/io/votable/connect.py
@@ -10,8 +10,7 @@
 from .tree import VOTableFile, Table as VOTable
 from .. import registry as io_registry
 from ...table import Table
-from ...table.column import BaseColumn
-from ...units import Quantity
+
 
 def is_votable(origin, filepath, fileobj, *args, **kwargs):
     """
@@ -140,14 +139,12 @@ def write_table_votable(input, output, table_id=None, overwrite=False,
         ``tabledata``.  See :ref:`votable-serialization`.
     """
 
-    # Not all tables with mixin columns are supported
+    # Tables with mixin columns are not supported
     if input.has_mixin_columns:
-        # Only those columns which are instances of BaseColumn or Quantity can be written
-        unsupported_cols = input.columns.not_isinstance(BaseColumn, Quantity)
-        if unsupported_cols:
-            unsupported_names = [col.info.name for col in unsupported_cols]
-            raise ValueError('cannot write table with mixin column(s) {0} to VOTable'
-                         .format(unsupported_names))
+        mixin_names = [name for name, col in input.columns.items()
+                       if not isinstance(col, input.ColumnClass)]
+        raise ValueError('cannot write table with mixin column(s) {0} to VOTable'
+                         .format(mixin_names))
 
     # Check if output file already exists
     if isinstance(output, six.string_types) and os.path.exists(output):
diff --git a/astropy/io/votable/tree.py b/astropy/io/votable/tree.py
index 46bb6835317..7183f03ff0a 100644
--- a/astropy/io/votable/tree.py
+++ b/astropy/io/votable/tree.py
@@ -1115,10 +1115,10 @@ def to_table_column(self, column):
         column.meta['values'] = meta
 
     def from_table_column(self, column):
-        if column.info.meta is None or 'values' not in column.info.meta:
+        if 'values' not in column.meta:
             return
 
-        meta = column.info.meta['values']
+        meta = column.meta['values']
         for key in ['ID', 'null']:
             val = meta.get(key, None)
             if val is not None:
@@ -1547,25 +1547,24 @@ def from_table_column(cls, votable, column):
         `astropy.table.Column` instance.
         """
         kwargs = {}
-        meta = column.info.meta or {}
         for key in ['ucd', 'width', 'precision', 'utype', 'xtype']:
-            val = meta.get(key, None)
+            val = column.meta.get(key, None)
             if val is not None:
                 kwargs[key] = val
         # TODO: Use the unit framework when available
-        if column.info.unit is not None:
-            kwargs['unit'] = column.info.unit
-        kwargs['name'] = column.info.name
+        if column.unit is not None:
+            kwargs['unit'] = column.unit
+        kwargs['name'] = column.name
         result = converters.table_column_to_votable_datatype(column)
         kwargs.update(result)
 
         field = cls(votable, **kwargs)
 
-        if column.info.description is not None:
-            field.description = column.info.description
+        if column.description is not None:
+            field.description = column.description
         field.values.from_table_column(column)
-        if 'links' in meta:
-            for link in meta['links']:
+        if 'links' in column.meta:
+            for link in column.meta['links']:
                 field.links.append(Link.from_table_column(link))
 
         # TODO: Parse format into precision and width
diff --git a/astropy/table/table.py b/astropy/table/table.py
index 1263b63b25c..1e47544d0cb 100644
--- a/astropy/table/table.py
+++ b/astropy/table/table.py
@@ -150,14 +150,14 @@ def keys(self):
     def values(self):
         return list(OrderedDict.values(self))
 
-    def isinstance(self, *cls):
+    def isinstance(self, cls):
         """
         Return a list of columns which are instances of the specified classes.
 
         Parameters
         ----------
-        *cls : argument list of Column classes
-            List of Column (including mixin) classes.
+        cls : class or tuple of classes
+            Column class (including mixin) or tuple of Column classes.
 
         Returns
         -------
@@ -167,14 +167,14 @@ def isinstance(self, *cls):
         cols = [col for col in self.values() if isinstance(col, cls)]
         return cols
 
-    def not_isinstance(self, *cls):
+    def not_isinstance(self, cls):
         """
         Return a list of columns which are not instances of the specified classes.
 
         Parameters
         ----------
-        *cls : argument list of Column classes
-            List of Column (including mixin) classes.
+        cls : class or tuple of classes
+            Column class (including mixin) or tuple of Column classes.
 
         Returns
         -------
diff --git a/astropy/table/tests/test_mixin.py b/astropy/table/tests/test_mixin.py
index 913492d7ccc..1214a8eed72 100644
--- a/astropy/table/tests/test_mixin.py
+++ b/astropy/table/tests/test_mixin.py
@@ -105,9 +105,10 @@ def test_io_ascii_write():
 
 def test_io_quantity_write(tmpdir):
     """
-    Test that table with Quantity mixin column can be written by io.votable,
-    io.fits, and io.misc.hdf5. No validation of the output is done,
-    this just confirms no exceptions.
+    Test that table with Quantity mixin column can be written by io.fits,
+    but not by io.votable and io.misc.hdf5. Validation of the output is done.
+    Test that io.fits writes a table containing Quantity mixin columns that can
+    be round-tripped (metadata unit).
     """
     t = QTable()
     t['a'] = u.Quantity([1,2,4], unit='Angstrom')
@@ -116,17 +117,17 @@ def test_io_quantity_write(tmpdir):
     open(filename, 'w').close()
 
     for fmt in ('fits', 'votable', 'hdf5'):
-        if fmt == 'hdf5' and not HAS_H5PY:
-            continue
-        out = StringIO()
-        if fmt == 'hdf5':
-            t.write(filename, format=fmt, path='data', overwrite=True)
-            continue
-        t.write(filename, format=fmt, overwrite=True)
         if fmt == 'fits':
+            t.write(filename, format=fmt, overwrite=True)
             qt = QTable.read(filename, format=fmt)
             assert isinstance(qt['a'], u.Quantity)
             assert qt['a'].unit == 'Angstrom'
+            continue
+        if fmt == 'hdf5' and not HAS_H5PY:
+            continue
+        with pytest.raises(ValueError) as err:
+            t.write(filename, format=fmt, overwrite=True)
+        assert 'cannot write table with mixin column(s)' in str(err.value)
 
 
 def test_io_write_fail(mixin_cols):
@@ -137,7 +138,7 @@ def test_io_write_fail(mixin_cols):
     t = QTable(mixin_cols)
     #Only do this test if there are unsupported column types (i.e. anything besides
     #BaseColumn or Quantity subclasses.
-    unsupported_cols = t.columns.not_isinstance(BaseColumn, u.Quantity)
+    unsupported_cols = t.columns.not_isinstance((BaseColumn, u.Quantity))
     if not unsupported_cols:
         pytest.skip("no unsupported column types")
     for fmt in ('fits', 'votable', 'hdf5'):