How to access multiple tuples in Bolt

[Dcoder-D]

My topology in short is as follows:

from streamparse import Topology, Spout, Bolt, Stream


class Dataspout(Spout):
     outputs = [Stream(fields=['to_validate'], name='to_validate'),
                Stream(fields=['to_combine'],  name='to_combine')]

     def next_tuple(self):
          ###Does something
          self.emit(value_for_validate, stream='to_validate')
          self.emit(value_for_combine,  stream='to_combine')


class ValidateBolt(Bolt):
     outputs = [Stream(fields=['validated1', 'validated2'], name='validated')]

     def process(self, tup):
          ###Does something
          self.emit([a_list, b_list], stream='validated')     


class CombineBolt(Bolt):
     outputs = []
     
     def process(self, tup):
          """----------Highlight: My question is here-----------"""


class MyTopology(Topology):
     data_spout    = Dataspout.spec()
     validate_bolt = ValidateBolt.spec(inputs=[data_spout['to_validate']])
     combine_bolt  = CombineBolt.spec(inputs=[validate_bolt['validated'],
                                              data_spout['to_combine']]) 

Ideally, in the highlighted part I wish I could access the [a_list, b_list] emitted by validate_bolt and the value_for_combine emitted by data_spout in my combine_bolt. However, in the process(self, tup) function of CombineBolt, the tup.values only contains the tuple emitted by data_spout. (When I print out tup.values, it writes Data_Spoutto_validateTuple(to_validate=...) ) How could I access the tuple emitted by ValidationBolt?