class_docstr: Interpret AST nodes to gleam useful debugging information. 
class_docstr_tok: ["Interpret","AST","nodes","to","gleam","useful","debugging","information","."]
code: def visit_UnaryOp(self, unary):
      pattern = unary_map[unary.op.__class__]
      operand_explanation, operand_result = self.visit(unary.operand)
      explanation = pattern % (operand_explanation,)
      co = self._compile(pattern % ("__exprinfo_expr",))
      try:
          result = self.frame.eval(co, __exprinfo_expr=operand_result)
      except Exception:
          raise Failure(explanation)
      return explanation, result
  
imports: import sys
  import ast
  import py
  from py._code.assertion import _format_explanation, BuiltinAssertionError
label_desc: Use image node_id 9 for calling the DebugInterpreter obj's underlying member method code with example usage: obj.visit_UnaryOp(unary) and returns: explanation,  result