code: def __parse_request_range(range_header_text):
      
  
      left = None
      right = None
  
      if not range_header_text:
          return left, right
  
      range_header_text = range_header_text.strip()
      if not range_header_text.startswith('bytes'):
          return left, right
  
      components = range_header_text.split("=")
      if len(components) != 2:
          return left, right
  
      components = components[1].split("-")
  
      try:
          right = int(components[1])
      except:
          pass
  
      try:
          left = int(components[0])
      except:
          pass
  
      return left, right
docs: Return a tuple describing the byte range requested in a GET request
      If the range is open ended on the left or right side, then a value of None
      will be set.
      RFC7233: http://svn.tools.ietf.org/svn/wg/httpbis/specs/rfc7233.html#header.range
      Examples:
        Range : bytes=1024-
        Range : bytes=10-20
        Range : bytes=-999