Tidy up "for" tag

[Chris Beaven]

Just a follow-up patch related to #3523 (Extend "for" tag to allow unpacking of lists) and it's recent checkin.

Currently there is a small difference between the single behaviour and the unpacking behaviour: for unpacking, the context scope is popped every loop iteration. This patch changes this behaviour to use the same scope throughout the loop's lifespan (making it behave more like the older single behaviour).

The patch also tidies up the comma-splitting through the use of re.split.

[Jacob]

Hrm... this is a tricky one. The re.split change is obviously good, but the other one looks like it'll be a bit slower, which I don't like.

[Chris Beaven]

Going back through some of my old tickets.

If anything, I'd say this would be a speed increase. Currently, we're pushing and popping the context like crazy for unpacked fors. The second for is a safety method which is mostly a noop (except for a len() call) for most normal usage.

Apart from that, it is also a subtle change in behaviour (new items placed on the context are local to each iteration unpacked fors).

[Chris Beaven]

This is much less important now we have a RenderContext which should be used if you really care about context. Due to the age of the ticket, switching back to the original behavior would potentially cause more side-effects in third party projects than leaving it as-is.

The ticket is being left open because as jacob says the split change is good. So the "improved" patch just needs to do that.

[Chris Beaven]

(In [14656]) Fixed #4552 -- minor tidy up of the {% for %} tag's comma splitting