the "total" function does not work on a table which generated by filter.

[Fatalerr]

for example:

t1 = TableFu()
t2 = t1.filter(type='xxx')
t2.total('column_name')    

the last cause will raise an error such like:

D:\tools\WinPython-32bit-2.7.3.3\python-2.7.3\lib\site-packages\table_fu\__init__.pyc in __getitem__(self, column_name)
     343         datum = self.get(column_name)
     344         if datum is None:
--> 345             raise KeyError("%s isn't a column in this table" % column_name)
     346         else:
     347             return datum

     KeyError: "3 isn't a column in this table"