input: 
  from typing import List
  
  
  def eval_expr(expr: str) -> float:
      """Evaluates a given string containing a numerical expression and returns the result.
      >>> eval_expr("2 + 2")
      4.0
      >>> eval_expr("10 * 5 - 3")
      47.0
      """
  
output:     return float(eval(expr))