code: def singular(plural):
      
      if plural.endswith('ies'):
          return plural[:-3] + 'y'
      if plural.endswith('s'):
          return plural[:-1]
      raise ValueError('unknown plural form %r' % (plural,))
docs: Take a plural English word and turn it into singular
  
      Obviously, this doesn't work in general. It know just enough words to
      generate XML tag names for list items. For example, if we have an element
      called 'tracks' in the response, it will be serialized as a list without
      named items in JSON, but we need names for items in XML, so those will be
      called 'track'.