do { } while(0);

This is often seen in kernel code. Here's a nice explanation from the linux kernel newbies FAQ:

http://kernelnewbies.org/FAQ/DoWhile0

Python's "for-else" and "while-else" loops

Almost every imperative procedural language has a for and while kind of loop. But Python is the only language that has an "else" attached to for or while. And the else does not have what you would think is the intuitive meaning (it doesn't get executed only if the for or while is never executed i.e. the condition is false to begin with). Rather, if the for or while ends normally without a break statement (i.e. it ends because its condition becomes false), the else is executed.

To me with my beginners knowledge of Python, it seems a bit unclean, and out of place for a precise and tightly controlled feature set language like Python. Let's see if I am proven wrong when I know more.

Edit on 4/8:
As expected, I was proven wrong. Turns out there is a very useful common idiom that is addressed by this. We typically code a "did_it_happen_flag" in a for or a while loop (pseudocode)


while(...) {

  if(...) {

    did_it_happen = TRUE;

    break;

  }

}



if(!did_it_happen) {

  printf("It didn't :-(");

  // Do something useful

}








This can be coded in Python like this:


while (...):

  if(...) : break

  ...

else:

  print "It didn't :-("



This way that extra check is not required - if the break were never hit, the else associated with the while takes care of taking the action we need.