class_docstr: Start node for a set of Streams
  
  Source nodes emit data into other nodes. They typically get this data
  by polling external sources, and are necessarily run by an event loop.
  
  Parameters
  ----------
  start: bool
      Whether to call the run method immediately. If False, nothing
      will happen until ``source.start()`` is called.
class_docstr_tok: ["Start","node","for","a","set","of","Streams","Source","nodes","emit","data","into","other","nodes",".","They","typically","get","this","data","by","polling","external","sources",",","and","are","necessarily","run","by","an","event","loop",".","Parameters","--","--","--","--","--","start",":","bool","Whether","to","call","the","run","method","immediately",".","If","False",",","nothing","will","happen","until","``","source.start","(",")","``","is","called","."]
docstr: start polling
  
  If already running, this has no effect. If the source was started and then
  stopped again, this will restart the ``self.run`` coroutine.
docstr_tok: ["start","polling","If","already","running",",","this","has","no","effect",".","If","the","source","was","started","and","then","stopped","again",",","this","will","restart","the","``","self.run","``","coroutine","."]
code: def start(self):
      """start polling
  
      If already running, this has no effect. If the source was started and then
      stopped again, this will restart the ``self.run`` coroutine.
      """
      if self.stopped:
          self.stopped = False
          self.started = True
          self.loop.add_callback(self.run)
  
imports: import asyncio
  from glob import glob
  import queue
  import os
  import time
  from tornado import gen
  import weakref
  from .core import Stream, convert_interval, RefCounter, sync
label_desc: Use image node_id 3 for calling the Source obj's underlying member method code with example usage: obj.start() without return types