input: def num_common_chars(str1: str, str2: str) -> int:
      """ Finds the total number of common characters present in both strings
      >>> num_common_chars("hello", "world")
      4
      >>> num_common_chars("abc", "def")
      0
      >>> num_common_chars("aaabbc", "aab")
      3
      """
output:     set1 = set(str1)
      set2 = set(str2)
      common_chars = set1 & set2
      return len(common_chars)