transform.py

all_securities = Security.objects.filter(company=company).for_report().iterator()

def flatten(*args):
    def transform_pipeline(mdl):
        data = FlatData()
        for fn in args:
            fn(data, mdl)
        return data
    return transform_pipeline

def add_issue_date(flat, mdl):
    flat.issue_date = mdl.get_issue_date()

def add_label(flat, mdl):
    flat.label = mdl.get_label()

flat_securities = (
  conduit(all_securities)
      ...
      .map(
          flatten(
              add_issue_date,
              add_label
          )
      )
      ...
)