Xml

<button name="import_xls" string="Import" type="object" />

Py

import base64
import xlrd

    xls_file = fields.Binary('File')

    def import_xls(self):
         wb = xlrd.open_workbook(file_contents=base64.decodestring(self.xls_file))
         for sheet in wb.sheets():
             for row in range(sheet.nrows):
                 for col in range(sheet.ncols):
                     print  (sheet.cell(row,col).value)

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