Best way to check that you are at the beginning (the end) of an iterable?

[Laurent]

I totally understand the performance issue that an hypothetical "istail" would bring, even if I think it would just be the programmer's responsibility not to use it when it's not certain that an end can be detected. 
But I don't see why *adding* something like "ishead" would be so bad (at worse by using a boolean somewhere as you mentioned).

Anyway I was just asking if there is something better than enumerate. So the answer is no? The fact that I have to create a tuple with an incrementing integer for something as simple as checking that I'm at the head just sounds awfully unpythonic to me.