code: def get(self, terser):
          
          key = terser
          # if the expression in not found n the qualified names
          # find the alias
          if terser not in self.data and terser in self.aliasKeys:
              key = self.aliasKeys[terser]
  
          value = self.data.get(key, None)
  
          # if the value is not found, it can be a partial terser
          if value:
              return value
          else:
              # find the values : simple startswith : should it be a regexp ? (more powerful, more slower)
              values = list(filter(lambda k: k.startswith(key), self.aliasKeys))
              if len(values) > 0:
                  return values
              else:
                  return None
docs: Get a value in the HL7 dictionary. The terser can be fully qualified or not.
              Fully qualified : OBR[1]-10-01
              Simpliest form  : OBR-10-1 (in this case, 1 uniq segment OBR is present in the HL7 message)
  
              :return : the value or a list of values. Otherwise None.