code: def assert_not_in(first, second, msg_fmt="{msg}"):
      
      if first in second:
          msg = "{!r} is in {!r}".format(first, second)
          fail(msg_fmt.format(msg=msg, first=first, second=second))
docs: Fail if first is in a collection second.
  
      >>> assert_not_in("bar", [4, "foo", {}])
      >>> assert_not_in("foo", [4, "foo", {}])
      Traceback (most recent call last):
          ...
      AssertionError: 'foo' is in [4, 'foo', {}]
  
      The following msg_fmt arguments are supported:
      * msg - the default error message
      * first - the element looked for
      * second - the container looked in