input: from typing import List
  
  def num_common_chars(str1: str, str2: str) -> int:
      """ Find the total number of common characters present in both strings.
      >>> num_common_chars('hello', 'bello')
      4
      >>> num_common_chars('apple', 'orange')
      3
      """
output:     common_chars = set(str1) & set(str2)
      return len(common_chars)