code: def _construct_post_data(self):
          
          definitions = [msm.build_api_struct() for msm in self.measurements]
          probes = [source.build_api_struct() for source in self.sources]
          self.post_data = {
              "definitions": definitions,
              "probes": probes,
              "is_oneoff": self.is_oneoff
          }
  
          if self.is_oneoff:
              self.post_data.update({"is_oneoff": self.is_oneoff})
  
          if self.start_time:
              self.post_data.update(
                  {"start_time": int(calendar.timegm(self.start_time.timetuple()))}
              )
          if self.stop_time:
              self.post_data.update(
                  {"stop_time": int(calendar.timegm(self.stop_time.timetuple()))}
              )
  
          if self.bill_to:
              self.post_data.update({"bill_to": self.bill_to})
docs: Constructs the data structure that is required from the atlas API based
          on measurements, sources and times user has specified.