Caught me out!
And -- for the edification of future readers -- in addition to conj. and prep., "but" can also be or 'be used as':
in reply to Re^2: A few grammar checks for strings
in thread A few grammar checks for strings
- a noun "I'll take no but as an answer"
- a pronoun "no one but has his fault..." (or, depending on your ed. of Shakespeare, "nobody but..."
- an adverb "That's but a little tree."