def normalize(form, unistr):
"""
Return the normal form 'form' for the Unicode string unistr. Valid
values for form are 'NFC', 'NFKC', 'NFD', and 'NFKD'.
"""
try:
normalizer_form = _forms[form]
except KeyError:
raise ValueError('invalid normalization form')
return Normalizer.normalize(unistr, normalizer_form)
