code: def p_field_id(self, p):
          '''field_id : INTCONSTANT ':'
                      | '''
          if len(p) == 3:
  
              if p[1] == 0:
                  # Prevent users from ever using field ID 0. It's reserved for
                  # internal use only.
                  raise ThriftParserError(
                      'Line %d: Field ID 0 is reserved for internal use.'
                      % p.lineno(1)
                  )
  
              p[0] = p[1]
          else:
              p[0] = Nonf p_field_id(self, p):
          '''field_id : INTCONSTANT ':'
                      | '''
          if len(p) == 3:
  
              if p[1] == 0:
                  # Prevent users from ever using field ID 0. It's reserved for
                  # internal use only.
                  raise ThriftParserError(
                      'Line %d: Field ID 0 is reserved for internal use.'
                      % p.lineno(1)
                  )
  
              p[0] = p[1]
          else:
              p[0] = None
docs: field_id : INTCONSTANT ':'
                      |