class_docstr: Class that chains datas
class_docstr_tok: ["Class","that","chains","datas"]
code: def start(self):
      super(Chainer, self).start()
      for d in self._args:
          d.setenvironment(self._env)
          d._start()
  
      # put the references in a separate list to have pops
      self._ds = list(self._args)
      self._d = self._ds.pop(0) if self._ds else None
      self._lastdt = datetime.min
  
file_path: backtrader/backtrader/feeds/chainer.py
imports: from __future__ import absolute_import, division, print_function, unicode_literals
  from datetime import datetime
  import backtrader
  from backtrader.utils.py3 import range
label_desc: Use image node_id 3 for calling the Chainer obj's underlying member method code with example usage: obj.start() without return types