input: def validate_brackets(brackets: str):
      """ brackets is a string containing "<" and ">" characters.
      return True if each opening bracket has a matching closing bracket.
  
      >>> validate_brackets("<")
      False
      >>> validate_brackets("<>")
      True
      >>> validate_brackets("<<><>>")
      True
      >>> validate_brackets("><<>")
      False
      """
output:     stack = []
      for bracket in brackets:
          if bracket == '<':
              stack.append(bracket)
          elif bracket == '>':
              if not stack:
                  return False
              stack.pop()
      return not stack