code: def current_securities(self, dt):
      for kd in self._knowledge_dates:
          if dt < kd:
              break
          if kd in self._cache:
              self._current_set = self._cache[kd]
              continue
  
          for effective_date, changes in iter(self.data[kd].items()):
              self.update_current(
                  effective_date, changes["add"], self._current_set.add
              )
  
              self.update_current(
                  effective_date,
                  changes["delete"],
                  self._current_set.remove,
              )
  
          self._cache[kd] = self._current_set
      return self._current_set
  
imports: import warnings
  from datetime import datetime
  from os import listdir
  import os.path
  import pandas
  import pytz
  import catalyst
  from catalyst.errors import SymbolNotFound
  from catalyst.finance.asset_restrictions import SecurityListRestrictions
  from catalyst.catalyst_warnings import ZiplineDeprecationWarning
label_desc: Use image node_id 5 for calling the SecurityList obj's underlying member method code with example usage: obj.current_securities(dt) and returns: self