<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _exec_eval(data, expr):
 """ Internal function to isolate an exec. Executes ``data`` and returns the ``expr`` evaluation afterwards. """

  ns = {}
  exec(data, ns)
  return eval(expr, ns)