Ascii Encoding Error with UTF-8 encoder

[Mike Currie]

Can anyone explain why I'm getting an ascii encoding error when I'm trying 
to write out using a UTF-8 encoder?

Thanks

Python 2.4.3 (#69, Mar 29 2006, 17:35:34) [MSC v.1310 32 bit (Intel)] on
win32
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>>> filterMap = {}
>>> for i in range(0,255):
...     filterMap[chr(i)] = chr(i)
...
>>> filterMap[chr(9)] = chr(136)
>>> filterMap[chr(10)] = chr(133)
>>> filterMap[chr(136)] = chr(9)
>>> filterMap[chr(133)] = chr(10)
>>> line = '''this      has
... tabs        and     line
... breaks'''
>>> filteredLine = ''.join([ filterMap[a] for a in line])
>>> import codecs
>>> f = codecs.open('foo.txt', 'wU', 'utf-8')
>>> print filteredLine
thisêhasêàtabsêandêlineàbreaks
>>> f.write(filteredLine)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "C:\Python24\lib\codecs.py", line 501, in write
    return self.writer.write(data)
  File "C:\Python24\lib\codecs.py", line 178, in write
    data, consumed = self.encode(object, self.errors)
UnicodeDecodeError: 'ascii' codec can't decode byte 0x88 in position 4:
ordinal
not in range(128)