code: def select_event(
      event     = None,
      selection = "ejets"
      ):
      
      if selection == "ejets":
          # Require single lepton.
          # Require >= 4 jets.
          if \
              0 < len(event.el_pt) < 2 and \
              len(event.jet_pt) >= 4 and \
              len(event.ljet_m) >= 1:
              return True
          else:
              return False
docs: Select a HEP event.