I have the same issue, don't understand why there's a "< 0". I'm not sure if there is anything I can do to make the code work.

For those that need the Python dictionary:
d = {
'ą':'a',
'ć':'c',
'ę':'e',
'ł':'l',
'ń':'n',
'ó':'o',
'ś':'s',
'ź':'z',
'ż':'z'
}