input: Write a function to evaluate a numerical expression represented as a string and return the result.
  
  def eval_expr(expr):
     return eval(expr)
  
  assert eval_expr("3 + 4 * 2")==11
  assert eval_expr("(3 + 4) * 2")==14
  assert eval_expr("10 / 2 + 3")==8
  assert eval_expr("2 ** 3 - 4")==4
  assert eval_expr("5 % 2 + 1")==2
output: def eval_expr(expr):
      return eval(expr)