code: def file_write():
      watcher = WatcherBase()
      stream = watcher.create_stream(
          expr="lambda vars:(vars.x, vars.x**2)",
          devices=[r"c:\temp\obs.txt"],
      )
  
      for i in range(5):
          watcher.observe(x=i)
  
file_path: tensorwatch/test/files/file_stream.py
imports: from tensorwatch.watcher_base import WatcherBase
  from tensorwatch.stream import Stream
  from tensorwatch.file_stream import FileStream
  from tensorwatch import LinePlot
  from tensorwatch.image_utils import plt_loop
  import tensorwatch
label_desc: Use image node_id 1 for calling a global function with example usage: file_write() without return types