这个except 相当于but,这是少数的可以跟不定式的词.但是因为前面有实意动词did/do/to do 介词后面的不定式符号to 省略.如He did nothing but sleep./He had nothing to do but wait./ He had no choice but to sleep.
大部分情况下except 和but 可以替换,如all the class went there except/but Tom. there was nothing in the room except /but a chair. 但是except 后面可以跟that 从句,but 不可以,如I know nothing about him except that he is from America.