code: def __init__(self):
      if CanvasManager.SINGLETON is not None:
          raise Exception("Can only create one canvas manager.")
      CanvasManager.SINGLETON = self
      QtCore.QObject.__init__(self)
      self.canvases = weakref.WeakValueDictionary()
  
file_path: pyqtgraph/pyqtgraph/canvas/CanvasManager.py
imports: from ..Qt import QtCore, QtWidgets
  import weakref
label_desc: Use image node_id 1 to create a new CanvasManager object from inherited base classes: QtCore with example: obj = CanvasManager()