input: from typing import List
  
  def eval_expr(expr: str) -> float:
      """Takes a string containing a numerical expression and returns the result.
      >>> eval_expr("2 + 3 * 4")
      14.0
      >>> eval_expr("10 / 2")
      5.0
      >>> eval_expr("5 - 2 + 3")
      6.0
      """
output:     return float(eval(expr))