Fixing tests

Posted Apr 12, 2012 19:57 UTC (Thu) by dskoll (subscriber, #1630)
In reply to: Fixing tests by man_ls
Parent article: Python 2.6.8, 2.7.3, 3.1.5, and 3.2.3 security release

I believe it's an implementation artifact. I don't think JavaScript hashes guarantee any kind of order.

PHP (yuck) arrays do seem to guarantee an order. PHP is completely broken and confusingly combines hashes and arrays into the same data structure. Internally, it keeps extra pointers around so you can pull out elements in the same order you put them in. So a PHP hash bucket costs at least two pointers worth of space more than it should, not to mention the constant time overhead of maintaining the two extra pointers.

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Fixing tests

Posted Apr 12, 2012 20:22 UTC (Thu) by man_ls (guest, #15091) [Link] (5 responses)

My mistake, Gecko and WebKit return keys in insertion order, not alphabetical. And it is not javascript arrays but objects; as you probably know, Javascript Does Not Support Associative Arrays

By the way, PHP also returns keys in insertion order, this time with real associative arrays. It is a nice feature IMHO; it may have some overhead but the results are much more intuitive than with Python's dicts. In a certain sense these other languages are hiding the details of the implementation, so that e.g. primitive testing schemes do not rely on the particular hashing function used.

Fixing tests

Posted Apr 12, 2012 20:41 UTC (Thu) by spaetz (guest, #32870) [Link] (2 responses)

Why dont you use OrderedDicts from python's collections module, if that is what you want?

Fixing tests

Posted Apr 12, 2012 20:50 UTC (Thu) by man_ls (guest, #15091) [Link] (1 responses)

Why, OrderedDicts didn't exist when I began coding eLyXer (and Python in general). Even if they had, they are new in Python 3.1 and I am still using Python 2. And I wanted to maintain compatibility back to Python 2.4 (Debian oldstable at the time), now back to Python 2.5.

Also, I did not know that I might eventually need insertion order at the time. I am guessing that also pure inertia might have played a role, although if OrderedDicts keep the same interface (and it appears that they do) that would make the switch quite painless. So I have at least three good reasons and two good excuses :)

Fixing tests

Posted Apr 13, 2012 6:54 UTC (Fri) by cathectic (guest, #40543) [Link]

There is a backport of it for older Python releases all the way back to 2.4:

http://pypi.python.org/pypi/ordereddict

Fixing tests

Posted Apr 13, 2012 13:10 UTC (Fri) by dskoll (subscriber, #1630) [Link] (1 responses)

By the way, PHP also returns keys in insertion order, this time with real associative arrays. It is a nice feature IMHO

I don't like the fact that PHP treats arrays and hashes as the same thing. I would prefer a different syntax for a numerically-indexed array than for an associative array. I would also rather that hashes don't return keys in insertion order by default. PHP should provide a separate data type similar to Python's OrderedDict for those times you want insertion order respected and are willing to pay the overhead.

Fixing tests

Posted Apr 13, 2012 14:17 UTC (Fri) by cortana (subscriber, #24596) [Link]

Let's not get ahead of ourselves. I'd much prefer that PHP provide basic things like a working < operator before moving on to such advanced features!