input: 
  def num_common_chars(str1: str, str2: str) -> int:
      """ Given two strings, find the total number of common characters present in both strings.
      >>> num_common_chars('hello', 'world')
      3
      >>> num_common_chars('abc', 'def')
      0
      >>> num_common_chars('shared', 'dare')
      4
      """
  
output:     common_chars = set(str1) & set(str2)
      return len(common_chars)