code: def _parse_with_unset_ctx(expr_source):
      ast_node = parser.parse_expression(expr_source)
      _CtxClearer().visit(ast_node)
      return ast_node
  
imports: import imp
  import unittest
  import gast
  from nvidia.dali._autograph.pyct import gast_util
  from nvidia.dali._autograph.pyct import loader
  from nvidia.dali._autograph.pyct import parser
  from nvidia.dali._autograph.pyct import qual_names
  from nvidia.dali._autograph.pyct import templates
label_desc: Use image node_id 1 for calling a global function with example usage: _parse_with_unset_ctx(expr_source) and returns: ast_node