code: def copy_u(u, out):
      """Builtin message function that computes message using source node
      feature.
  
      Parameters
      ----------
      u : str
          The source feature field.
      out : str
          The output message field.
  
      Examples
      --------
      >>> import dgl
      >>> message_func = dgl.function.copy_u('h', 'm')
  
      The above example is equivalent to the following user defined function:
  
      >>> def message_func(edges):
      >>>     return {'m': edges.src['h']}
      """
      return CopyMessageFunction(TargetCode.SRC, u, out)
  
file_path: dgl/python/dgl/function/message.py
imports: from __future__ import absolute_import
  import sys
  from itertools import product
  from .base import BuiltinFunction, TargetCode
label_desc: Use image node_id 1 for calling a global function with example usage: copy_u(u, out) and returns: CopyMessageFunction