I got a tiny script in ArcGIS which creates a hyperlink.
My code:
def Befahrung(value1, value2):
    if value1 is '':
        return ''
    else:
        return "G:\\Example\\" + str(value1) + "\\File_" + str(value2) + ".pdf"
The error (only when !Bezeichnun! contains a special character):
ERROR 000539: Error running expression: Befahrung(u" ",u"1155Mönch1")
Traceback (most recent call last):
  File "<expression>", line 1 in <module>
  File "<string>", line 5 in Befahrung
UnicodeEncodeError: 'ascii' codec can't encode character u'\xf6' in position 5: ordinal not in range(128)
!Bezeichnun! and !Auftrag! are both strings. It works very well until !Bezeichnun! contains a special character. I can't change the characters, I need to save them.
What do I have to change?
 
     
     
    