[web2py] How to retrieve data from FieldStorage

[vortex]

I would like to obtain the filename string from request.vars.xls_file
such as:

filename = request.vars.xls_file
"filename"      'backup_2011-02-08_11h24.xls'

but I get the FieldStorage:

filename = request.vars.xls_file
"filename"      FieldStorage: FieldStorage('xls_file',
'backup_2011-02-08_11h24.xls', '\\xd0\\...')

How do I get the filename only from FieldStorage?