Guido van Rossum wrote:
Simply put:
a += 1 IS NOT ATOMIC!
If that's the case, then why do we need augemented assignments at all ?
(I understood the atomicness being the main argument for introducing augmented assigns.)
Huh? Where did you get that idea? Can you point to a message where this was indicated?
It was advertised this way by Thomas: http://www.python.org/pipermail/python-list/2000-June/060680.html And since assignments in Python are thread safe, I thought it would only be natural for augemented assigns to also be thread safe which would have been a real advantage, since a=a+1 is not thread safe. All other uses simply boil down to reducing typing efforts, IMHO. (But that shouldn't keep you from adding it to the language ;-) Some comments:
The reason for introducing it is that it's been the single-most requested feature ever since Python's inception. I think the reason it's been requested so much is that it's a waste of typing skills as well as (and more importantly) unnecessary extra effort to deduce what's going on in code like
a.b.f().x[i] = a.b.f().x[i] + 1
This can be written as: result = a.b.f().x result[i] = result[i] + 1
Another important reason is that in cases like
a[long_and_expensive_call()] = a[long_and_expensive_call()] + 1
Dito for this one: i = long_and_expensive_call() a[i] = a[i] + 1
you want to avoid doing the long_and_expensive_call() twice. Introducing a temp variable reduces the readability of the code.
Not really... in fact if the name makes it clear what it refers too, it can augment the readbility. Besdies, a.b.f().x[i] isn't good style to begin with ;-)
Note that my proposed semantics guarantee that in
a[long_and_expensive_call()] += 1
the index is computed only once -- but this is not the same as atomicity (which has to do with other threads, signal handlers and similar asynchronous things).
Nevermind... I just wanted to hint at the added value of making these assignments atomic operations and not just an optimization of a = a + 1. -- Marc-Andre Lemburg ______________________________________________________________________ Business: http://www.lemburg.com/ Python Pages: http://www.lemburg.com/python/