code: def coderef_to_ecoclass(self, code, reference=None):
          
          mcls = None
          for (this_code,this_ref,cls) in self.mappings():
              if str(this_code) == str(code):
                  if this_ref  == reference:
                      return cls
                  if this_ref is None:
                      mcls = cls
                      
          return mcls
docs: Map a GAF code to an ECO class
  
          Arguments
          ---------
          code : str
              GAF evidence code, e.g. ISS, IDA
          reference: str
              CURIE for a reference for the evidence instance. E.g. GO_REF:0000001.
              Optional - If provided can give a mapping to a more specific ECO class
  
          Return
          ------
          str
              ECO class CURIE/ID