2014-11-29 11:36 GMT+08:00 Chris Angelico <ros...@gmail.com>: > You can use id() on any object. You are guaranteed to get back an > integer which is both stable and unique among all ids of objects that > exist at the same time as the one you called it on. For as long as the > object continues to exist, that number *will* stay the same. Sometimes > that's all you need; for instance, imagine a simple mail server which > produces logs like this: > > [142857] Beginning processing of message > [142857] Parsing headers > [314159] Beginning processing of message > [314159] Parsing headers > [142857] Storing in destination mailbox > [314159] Connecting to destination server > [142857] Finished processing of message > [314159] Message accepted by destination > [271871] Beginning processing of message > [314159] Finished processing of message > > You can easily see, from the initial numbers, what log lines are > associated with what messages. (Note that emails have their own IDs, > which could in theory be used, but the id() of an internal dict can be > used even before the email's ID has been read - as you see from the > example, a log entry for "Parsing headers" has to be made prior to > info from the headers being used.) It's not a problem if another > 142857 comes up later on; there's a very clear begin and end to the > message, and you're guaranteed that nothing can possibly be > interspersed with a colliding ID. > > In other implementations of Python, these numbers might look less > arbitrary (Jython, I believe, allocates them sequentially); but the > code will work just as well on any compliant implementation of the > language, because everything I've said above is a language guarantee, > not a CPython implementation detail. > > ChrisA
Thanks. Informed. The implementation dependent thing is "id(obj)" == virtual mem addr (which caused my bad feeling). Apparently have nothing to do with it here, though. And 'id' is seemingly great to differentiate each obj. -- 吾輩は猫である。ホームーページはhttp://introo.me。 -- https://mail.python.org/mailman/listinfo/python-list
