what is this UnicodeDecodeError:....?

[kath]

I have a number of excel files. In each file DATE is represented by
different name. I want to read the date from those different file. Also
the date is in different column in different file.

To identify the date field in different files I have created a file
called _globals where I keep all aliases for DATE in a array called
'alias_DATE'.

Array alias_DATE looks like,

alias_DATE=['TRADEDATE', 'Accounting Date', 'Date de VL','Datum',
'Kurs-datum', 'Date', 'Fecha Datos', 'Calculation Date', 'ClosingDate',
'Pricing Date', 'NAV Date', 'NAVDate', 'NAVDATE', 'ValuationDate',
'Datestamp', 'Fecha de Valoración', 'Kurs-','datum',
"""Kurs-\ndatum""", "Kurs-\ndatum"]

Now I want the index of the column where date is there.  I followed the
with followin code.


>>> b=xlrd.open_workbook('Santander_051206.xls')
>>> sh=b.sheet_by_index(0)
>>> sh.cell_value(rowx=0, colx=11)
u'Fecha de Valoraci\xf3n'
>>> val=sh.cell_value(rowx=0, colx=11)
>>> val
u'Fecha de Valoraci\xf3n'
>>> print val
Fecha de Valoración
>>> import _globals		# the file where I have stored my 'alias_DATE' array
>>> _globals.alias_DATE.index(val)
Traceback (most recent call last):
  File "<interactive input>", line 1, in ?
UnicodeDecodeError: 'ascii' codec can't decode byte 0xf3 in position
17: ordinal not in range(128)
>>>

Though I have matching value in the array, why I am getting this error.
Can any one please tell me why is this error, and how to get rid of
this error. Because I have some files which containing some more
special characters. 


Thank you in advance.
Sudhir.