class_docstr: Parameters
  ----------
  - trading_calendar : catalyst.utils.trading_calendar.TradingCalendar
  - asset_finder : catalyst.assets.AssetFinder
  - readers : dict
      A dict mapping Asset type to the corresponding
      [Minute|Session]BarReader
  - last_available_dt : pd.Timestamp or None, optional
      If not provided, infers it by using the min of the
      last_available_dt values of the underlying readers.
class_docstr_tok: ["Parameters","--","--","--","--","--","-","trading_calendar",":","catalyst.utils.trading_calendar.TradingCalendar","-","asset_finder",":","catalyst.assets.AssetFinder","-","readers",":","dict","A","dict","mapping","Asset","type","to","the","corresponding","[","Minute|Session","]","BarReader","-","last_available_dt",":","pd.Timestamp","or","None",",","optional","If","not","provided",",","infers","it","by","using","the","min","of","the","last_available_dt","values","of","the","underlying","readers","."]
code: def __init__(
      self,
      trading_calendar,
      asset_finder,
      readers,
      last_available_dt=None,
  ):
      self._trading_calendar = trading_calendar
      self._asset_finder = asset_finder
      self._readers = readers
      self._last_available_dt = last_available_dt
  
      for t, r in iteritems(self._readers):
          assert trading_calendar == r.trading_calendar, (
              "All readers must share target trading_calendar. "
              "Reader={0} for type={1} uses calendar={2} which does not "
              "match the desired shared calendar={3} ".format(
                  r, t, r.trading_calendar, trading_calendar
              )
          )
  
imports: from abc import ABCMeta, abstractmethod
  from numpy import full, nan, int64, float64, zeros
  from six import iteritems, with_metaclass
  from catalyst.utils.memoize import lazyval
label_desc: Use image node_id 1 to create a new AssetDispatchBarReader object from inherited base classes:  with example: obj = AssetDispatchBarReader(trading_calendar, asset_finder, readers, last_available_dt)