code: def is_builtin(func):
      """Return true if the function is a DGL builtin function."""
      return isinstance(func, fn.BuiltinFunction)
  
file_path: dgl/python/dgl/core.py
imports: import numpy
  from .None import backend, function, ops
  from .base import ALL, dgl_warning, DGLError, EID, is_all, NID
  from .frame import Frame
  from .udf import EdgeBatch, NodeBatch
label_desc: Use image node_id 1 for calling a global function with example usage: is_builtin(func) and returns: isinstance