Gary Herron wrote: >> Huh? How am I supposed to compare immutable types for identity then? Your >> bizarre instruction would prohibit: >> >> if something is None >> > > Just use: > > if something == None > > It does *exactly* the same thing.
Wrong. "something is None" is a pointer comparison. It's blindingly fast, and it will only return True if something is the same object as None. Any other object *must* return False. "something == None" calls something.__eq__(None), which is a method of arbitrary complexity, which may cause arbitrary side-effects. It can have false positives, where objects with unexpected __eq__ methods may return True, which is almost certainly not the intention of the function author and therefore a bug. [...] > If they use a couple "something==None" instead of "something is None" > in their code while learning Python, it won't hurt, Apart from the subtle bugs they introduce into their code. > and they can change > their style when they understand the difference. And meanwhile they > will skip traps newbies fall into when they don't understand these > things yet. How about teaching them the right reasons for using "is" instead of giving them false information by telling them they should never use it? -- Steven -- http://mail.python.org/mailman/listinfo/python-list
