code: def tokens(istr):
      
  
      # make a list of all alphanumeric tokens
      toks = re.findall(r'[^\*\\\+\-\^\(\)]+\(?', istr)
  
      # remove the functions
      return [t for t in toks if not t.endswith('(')]
docs: Same as tokenize, but returns only tokens
      (and at all parantheses levels).