code: def _is_valid_annotation(ann):
      if not isinstance(ann, dict):
          return False
      if not _is_rectangle_annotation(ann):
          # Not necessarily valid, but we bypass stricter checks (we simply do
          # not care about non-rectangle types)
          return True
      return (
          "coordinates" in ann
          and isinstance(ann["coordinates"], dict)
          and set(ann["coordinates"].keys())
          == {"x", "y", "width", "height"}
          and ann["coordinates"]["width"] > 0
          and ann["coordinates"]["height"] > 0
          and "label" in ann
      )
  
imports: from __future__ import print_function
  from __future__ import division
  from __future__ import absolute_import
  import turicreate
label_desc: Use image node_id 3 for calling a global function with example usage: _is_valid_annotation(ann) and returns: unknown, False, True