docstr: Parse the attribute line if it knows how. Returns the parsed
  attribute, or None.
  
  For nominal attributes, the attribute string would be like '{<attr_1>,
   <attr2>, <attr_3>}'.
docstr_tok: ["Parse","the","attribute","line","if","it","knows","how",".","Returns","the","parsed","attribute",",","or","None",".","For","nominal","attributes",",","the","attribute","string","would","be","like","'","{","<","attr_1",">",",","<","attr2",">",",","<","attr_3",">","}","'","."]
code: def parse_attribute(cls, name, attr_string):
      """
      Parse the attribute line if it knows how. Returns the parsed
      attribute, or None.
  
      For nominal attributes, the attribute string would be like '{<attr_1>,
       <attr2>, <attr_3>}'.
      """
      if attr_string[0] == "{":
          values = cls._get_nom_val(attr_string)
          return cls(name, values)
      else:
          return None
  
imports: import re
  import datetime
  import numpy
  import csv
  import ctypes
label_desc: Use image node_id 3 for calling the NominalAttribute obj's underlying member method code with example usage: obj.parse_attribute(cls, name, attr_string) and returns: cls, None