code: def free_vars(expr):
      """Get free Vars from expression expr in Post DFS order.
  
      Parameters
      ----------
      expr : tvm.relay.Expr
          The input expression
  
      Returns
      -------
      free : List[tvm.relay.Var]
          The list of free variables in post DFS order.
  
      Note
      ----
      The fact that Vars are post-DFS ordred are useful in
      neural networks: usually this means weights of previous
      are ordered first.
      """
      return _ffi_api.free_vars(expr)
  
imports: from ...ir import IRModule
  from ...relay import transform, build_module
  from ...runtime.ndarray import cpu
  from .None import _ffi_api
  from .feature import Feature
label_desc: Use image node_id 6 for calling a global function with example usage: free_vars(expr) and returns: _ffi_api