code: def from_detections_assignment(detections_1, detections_2, assignments):
          
          traces = []
  
          for d1n, d2n in six.iteritems(assignments):
              # check if the match is between existing cells
              if d1n < len(detections_1) and d2n < len(detections_2):
                  traces.append(Trace(detections_1[d1n], detections_2[d2n]))
  
          return traces
docs: Creates traces out of given assignment and cell data.