filtered traitlet

[jchuahtacc]

Added filtered traitlet which allows python client to retrieve indices of what is currently viewable (after filtering)

[TimShawver]

It seems like your code isn't working with grids that have a Timestamp index. I get the following error when running #2 under Example 1 in the demo notebook https://github.com/quantopian/qgrid/blob/master/qgrid_demo.ipynb

qgrid.show_grid(spy)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-9-7f2f26238472> in <module>()
----> 1 qgrid.show_grid(spy)

/Users/tshawver/repo/qgrid-master/qgrid/grid.pyc in show_grid(data_frame, show_toolbar, remote_js, precision, grid_options)
    205     grid = QGridWidget(df=data_frame, precision=precision,
    206                        grid_options=grid_options,
--> 207                        remote_js=remote_js)
    208 
    209     if show_toolbar:

/Users/tshawver/repo/qgrid-master/qgrid/grid.pyc in __init__(self, *args, **kwargs)
    249         self._selected_rows = []
    250         if self.df is not None:
--> 251             self._update_table()
    252 
    253     def _grid_options_default(self):

/Users/tshawver/repo/qgrid-master/qgrid/grid.pyc in _update_table(self)
    273             df.index.name = 'Index'
    274 
--> 275         self.filtered = df.index.tolist()
    276 
    277         if type(df.index) == pd.core.index.MultiIndex:

/usr/local/lib/python2.7/site-packages/traitlets/traitlets.pyc in __set__(self, obj, value)
    581             raise TraitError('The "%s" trait is read-only.' % self.name)
    582         else:
--> 583             self.set(obj, value)
    584 
    585     def _validate(self, obj, value):

/usr/local/lib/python2.7/site-packages/traitlets/traitlets.pyc in set(self, obj, value)
    570             # we explicitly compare silent to True just in case the equality
    571             # comparison above returns something other than True/False
--> 572             obj._notify_trait(self.name, old_value, new_value)
    573 
    574     def __set__(self, obj, value):

/usr/local/lib/python2.7/site-packages/traitlets/traitlets.pyc in _notify_trait(self, name, old_value, new_value)
   1135             new=new_value,
   1136             owner=self,
-> 1137             type='change',
   1138         ))
   1139 

/usr/local/lib/python2.7/site-packages/ipywidgets/widgets/widget.pyc in notify_change(self, change)
    366                 # Send new state to front-end
    367                 self.send_state(key=name)
--> 368         LoggingConfigurable.notify_change(self, change)
    369 
    370     #-------------------------------------------------------------------------

/usr/local/lib/python2.7/site-packages/traitlets/traitlets.pyc in notify_change(self, change)
   1172                 c = getattr(self, c.name)
   1173 
-> 1174             c(change)
   1175 
   1176     def _add_notifiers(self, handler, name, type):

/Users/tshawver/repo/qgrid-master/qgrid/grid.pyc in filtered_changed(self, change)
    394         self.filtered = [ ]
    395         for index in change['new']:
--> 396             self.filtered.append(int(index))
    397 

TypeError: int() argument must be a string or a number, not 'Timestamp'