input: Write a function to evaluate a numerical expression given as a string and return the result.
  
  assert eval_expr("10 + 20 * 3") == 70
  assert eval_expr("(10 + 20) * 3") == 90
  assert eval_expr("5 ** 2") == 25
  assert eval_expr("20 / 4 + 3") == 8.0
  assert eval_expr("100 - 50 * 2") == 0
  assert eval_expr("0") == 0
output: def eval_expr(expression):
      return eval(expression)