[Python-Dev] Dict access with double-dot (syntactic sugar)

[Jameson Quinn]

2011/3/24 Brian Curtin <brian.curtin at gmail.com>

> On Thu, Mar 24, 2011 at 06:40, Jameson Quinn <jameson.quinn at gmail.com>wrote:
>
>> "class attrdict" is a perennial dead-end for intermediate pythonistas who
>> want to save 3 characters/5 keystrokes for item access. Other languages such
>> as javascript allow "somedict.foo" to mean the same as "somedict['foo']", so
>> why not python? Well, there are a number of reasons why not, beginning with
>> all the magic method names in python.
>>
>> But saving keystrokes is still a reasonable goal.
>>
>
> Code is read far more often than it is written, so readability tends to
> count more than most other metrics.
>
> So what about a compromise? Allow "somedict..foo", with two dots, to take
>> that place. It still saves 2 characters (often 4 keystrokes; and I find even
>> ', "[", or "]" harder to type than ".").
>>
>
> I don't see the benefit, but maybe it'll save a few bytes in file size.
> Anyone reviewing your code now has to think "does this need one or two
> dots?"
>
>  Anyways, why not just do something like this:
>
> class AttrDict(dict):
>     def __getattr__(self, attr):
>         return super(AttrDict, self).__getitem__(attr)
>
> >>> d = AttrDict()
> >>> d["a"] = 1
> >>> d.a
> 1
>

There are a few reasons not to do it your way. For one, you could easily
forget about one of the built-in dict methods (e.g. d.get != d["get"]). For
another, if you look on the web, you'll find at least 15 different recipes
for that thing you just made, several of which have more-or-less subtle
errors waiting to get you. Furthermore, the whole point is to have this
available for built-in dicts. Say you get a dict as json - you can either
subclass your own json decoder, with all the pitfalls, or you can explicitly
pass the decoded dict to AttrDict, causing an extra object to be created and
obfuscating your code. And finally, who wants to copy that AttrDict code for
the 137th time?

As for the question of "one or two dots", it's exactly the same question you
face now with "dot or bracket", so I don't see the problem.

It's not merely a matter of saving keystrokes. To me, it would be actually
easier to read code in this style. When I'm doing things like accessing my
json data, that is essentially attribute access; why should my syntax
colorer color it the same as my UI strings?

In sum:
-Saves keystrokes
-saves bugs from miscooked recipes
-faster and less memory than any such recipe
-more-readable code
-very low-risk for old code

Jameson
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