code: def get_history_tags(self, exp, rep=0):
          
          history = self.get_history(exp, rep, 'all')
          return history.keys()
docs: returns all available tags (logging keys) of the given experiment 
              repetition. 
              
              Note: Technically, each repetition could have different
              tags, therefore the rep number can be passed in as parameter, 
              even though usually all repetitions have the same tags. The default 
              repetition is 0 and in most cases, can be omitted.