I need to change some characters that are not ASCII to \'_\'. For example,
Tannh‰user -> Tannh_user
To answer the question
'[\u0080-\uFFFF]'
will match any UTF-8 character not in the range of the first 128 characters
re.sub('[\u0080-\uFFFF]+', '_', x)
will replace any sequence of consecutive nonascii characters with an underscore