input: from typing import List
  
  def longest_string(str_list: List[str]) -> str:
      """ Find and return the longest string in the given list.
      >>> longest_string(['foo', 'test', 'longstring', 'bar'])
      'longstring'
      """
      longest_str = ''
      for s in str_list:
          if len(s) > len(longest_str):
              longest_str = s
      return longest_str
output:     longest_str = ''
      for s in str_list:
          if len(s) > len(longest_str):
              longest_str = s
      return longest_str