code: def split(values, separator=re.compile("[ ,]+")):
      
      if not isinstance(values, list):
          values = [values]
      return sum([separator.split(value) for value in values], [])
docs: Convert space-or-comma-separated values into a single list
  
      Common use case for this is merging content of options with multiple
      values allowed into a single list of strings thus allowing any of
      the formats below and converts them into ['a', 'b', 'c']::
  
          --option a --option b --option c ... ['a', 'b', 'c']
          --option a,b --option c ............ ['a,b', 'c']
          --option 'a b c' ................... ['a b c']
  
      Accepts both string and list. By default space and comma are used as
      value separators. Use any regular expression for custom separator.