to_hdf:[unicode] is not implemented as a table column
First,sorry for my bad english:)
I want to store data use DataFrame.to_hdf() function.
when i use df600000.to_hdf(path_or_buf='H:\store.h5',key='SH600000',format='f',mode='r+'),it works good,since i change format='t' will raise TypeError,why?
detail as followed:
## In [55]:df600000.to_hdf(path_or_buf='H:\store.h5',key='SH600000',format='t',mode='r+')

TypeError                                 Traceback (most recent call last)
<ipython-input-55-ce1cae8be680> in <module>()
----> 1 df600000.to_hdf(path_or_buf='H:\store.h5',key='SH600000',format='t',mode='r+')

D:\winpython\WinPython-32bit-2.7.6.4\python-2.7.6\lib\site-packages\pandas\core\generic.pyc in to_hdf(self, path_or_buf, key, *_kwargs)
    882 
    883         from pandas.io import pytables
--> 884         return pytables.to_hdf(path_or_buf, key, self, *_kwargs)
    885 
    886     def to_msgpack(self, path_or_buf=None, **kwargs):

D:\winpython\WinPython-32bit-2.7.6.4\python-2.7.6\lib\site-packages\pandas\io\pytables.pyc in to_hdf(path_or_buf, key, value, mode, complevel, complib, append, **kwargs)
    277         with get_store(path_or_buf, mode=mode, complevel=complevel,
    278                        complib=complib) as store:
--> 279             f(store)
    280     else:
    281         f(path_or_buf)

D:\winpython\WinPython-32bit-2.7.6.4\python-2.7.6\lib\site-packages\pandas\io\pytables.pyc in <lambda>(store)
    272         f = lambda store: store.append(key, value, *_kwargs)
    273     else:
--> 274         f = lambda store: store.put(key, value, *_kwargs)
    275 
    276     if isinstance(path_or_buf, string_types):

D:\winpython\WinPython-32bit-2.7.6.4\python-2.7.6\lib\site-packages\pandas\io\pytables.pyc in put(self, key, value, format, append, *_kwargs)
    819             format = get_option("io.hdf.default_format") or 'fixed'
    820         kwargs = self._validate_format(format, kwargs)
--> 821         self._write_to_group(key, value, append=append, *_kwargs)
    822 
    823     def remove(self, key, where=None, start=None, stop=None):

D:\winpython\WinPython-32bit-2.7.6.4\python-2.7.6\lib\site-packages\pandas\io\pytables.pyc in _write_to_group(self, key, value, format, index, append, complib, encoding, *_kwargs)
   1271 
   1272         # write the object
-> 1273         s.write(obj=value, append=append, complib=complib, *_kwargs)
   1274 
   1275         if s.is_table and index:

D:\winpython\WinPython-32bit-2.7.6.4\python-2.7.6\lib\site-packages\pandas\io\pytables.pyc in write(self, obj, axes, append, complib, complevel, fletcher32, min_itemsize, chunksize, expectedrows, dropna, *_kwargs)
   3576         self.create_axes(axes=axes, obj=obj, validate=append,
   3577                          min_itemsize=min_itemsize,
-> 3578                          *_kwargs)
   3579 
   3580         if not self.is_exists:

D:\winpython\WinPython-32bit-2.7.6.4\python-2.7.6\lib\site-packages\pandas\io\pytables.pyc in create_axes(self, axes, obj, validate, nan_rep, data_columns, min_itemsize, **kwargs)
   3271                 self.values_axes.append(col)
   3272             except (NotImplementedError, ValueError, TypeError) as e:
-> 3273                 raise e
   3274             except Exception as detail:
   3275                 raise Exception(

TypeError: [unicode] is not implemented as a table column

In [5]:df600000.dtypes
Out[5]:
trad_date     object
open         float64
high         float64
low          float64
close        float64
vol            int64
val          float64
dtype: object

In [51]: df600000[:5]

Out[51]:
trad_date   open    high    low close   vol val
0    2000-01-04  3.43    3.54    3.40    3.51    4496000     113946784
1    2000-01-05  3.51    3.56    3.45    3.47    5252800     134465424
2    2000-01-06  3.45    3.61    3.44    3.57    6229600     160059792
3    2000-01-07  3.61    3.77    3.58    3.69    21355300    575751104
4    2000-01-10  3.70    3.82    3.66    3.74    16539700    450453504
## INSTALLED VERSIONS

commit: None
python: 2.7.6.final.0
python-bits: 32
OS: Windows
OS-release: 7
machine: AMD64
processor: Intel64 Family 6 Model 42 Stepping 7, GenuineIntel
byteorder: little
LC_ALL: None
LANG: None

pandas: 0.13.1
Cython: 0.20.1
numpy: 1.8.1
scipy: 0.13.3
statsmodels: 0.5.0
IPython: 2.0.0
sphinx: 1.2.2
patsy: 0.2.1
scikits.timeseries: None
dateutil: 2.2
pytz: 2013.9
bottleneck: None
tables: 3.1.1
numexpr: 2.3.1
matplotlib: 1.3.1
openpyxl: None
xlrd: 0.9.3
xlwt: 0.7.5
xlsxwriter: None
sqlalchemy: 0.9.4
lxml: 3.3.5
bs4: 4.3.2
html5lib: None
bq: None
apiclient: None
