code: def last_word(text, include='alphanum_underscore'):
      
  
      if not text:   # Empty string
          return ''
  
      if text[-1].isspace():
          return ''
      else:
          regex = cleanup_regex[include]
          matches = regex.search(text)
          if matches:
              return matches.group(0)
          else:
              return ''
docs: Find the last word in a sentence.
      >>> last_word('abc')
      'abc'
      >>> last_word(' abc')
      'abc'
      >>> last_word('')
      ''
      >>> last_word(' ')
      ''
      >>> last_word('abc ')
      ''
      >>> last_word('abc def')
      'def'
      >>> last_word('abc def ')
      ''
      >>> last_word('abc def;')
      ''
      >>> last_word('bac $def')
      'def'
      >>> last_word('bac $def', include='most_punctuations')
      '$def'
      >>> last_word('bac \def', include='most_punctuations')
      '\\\\def'
      >>> last_word('bac \def;', include='most_punctuations')
      '\\\\def;'
      >>> last_word('bac::def', include='most_punctuations')
      'def'