input: Write a function to find the total number of common characters present in both strings. The function takes two strings as input and returns the count of characters that are present in both strings.
  
  def num_common_chars(str1, str2):
      common = 0
      for c in str1:
          if c in str2:
              common += 1
      return common
  
  assert num_common_chars("hello", "world")==2
  assert num_common_chars("abc", "def")==0
  assert num_common_chars("aaabbc", "abbcddd")==4
  assert num_common_chars("", "test")==0
  assert num_common_chars("python", "java")==2
output: def num_common_chars(str1, str2):
      common = 0
      for c in str1:
          if c in str2:
              common += 1
      return common