Pandas hdf functions should support the hdf5 ExternalLink functionality when reading/writing.
When attempting to use pandas.read_hdf() to read a link from an h5py created data file with an ExternalLink to an HDFStore() created entry, the following backtrace is received:

/Users/xxx/.pyenv/versions/anaconda/lib/python2.7/site-packages/pandas/io/pytables.pyc in select(self, key, where, start, stop, columns, iterator, chunksize, auto_close, **kwargs)
    618         # create the storer and axes
    619         where = _ensure_term(where)
--> 620         s = self._create_storer(group)
    621         s.infer_axes()
    622 

/Users/xxx/.pyenv/versions/anaconda/lib/python2.7/site-packages/pandas/io/pytables.pyc in _create_storer(self, group, format, value, append, **kwargs)
   1119             )
   1120 
-> 1121         pt = _ensure_decoded(getattr(group._v_attrs, 'pandas_type', None))
   1122         tt = _ensure_decoded(getattr(group._v_attrs, 'table_type', None))
   1123 

/Users/xxx/.pyenv/versions/anaconda/lib/python2.7/site-packages/tables/link.pyc in **getattr**(self, name)
     77             def **getattr**(self, name):
     78                 raise KeyError("you cannot get attributes from this "
---> 79                                "`%s` instance" % self.**class**.**name**)
     80 
     81             def **setattr**(self, name, value):

KeyError: 'you cannot get attributes from this `NoAttrs` instance'

In this example, 'store.h5' was created with HDFStore() and a single Series was stored in it at the location '/banana'. h5py.File was then used to create 'external.h5' with a single entry for /external that pointed to store.h5:/banana using h5py.ExternalLink.

In my use case, I had written code to parse and store some complex data and associated metadata in hdf5 using h5py. My intention was then to read that raw data in using pandas and then re-store the cooked data using HDFStore.

Unfortunately, pandas HDFStore() did not like the metadata in my h5py written file.

--snip--
/Users/xxx/.pyenv/versions/anaconda/lib/python2.7/site-packages/tables/attributeset.py:294: DataTypeWarning: Unsupported type for attribute 'is_key' in node 'some_node'. Offending HDF5 class: 8
  value = self._g_getattr(self._v_node, name)
--snip--

I expected that I could work around this by simply storing the pandas content in a native HDFStore() written file and use ExternalLinks in the parent file. Unfortunately, that did not work properly either.

This is with pandas '0.13.0'.

Thanks!

-jbl 
