[Python-ideas] possible attribute-oriented class
steve at pearwood.info
Tue Sep 8 02:15:10 CEST 2009
On Mon, 7 Sep 2009 09:37:35 am Jan Kaliszewski wrote:
> 06-09-2009 o 20:20:21 Ethan Furman <ethan at stoneleaf.us> wrote:
> > ... I love being able to type
> > current_record.full_name == last_record.full_name
> > instead of
> > current_record['full_name'] == last_record['full_name']
> Me too, and I suppose many people too...
> The latter:
> * makes your code less readable if there is high density of such
> * makes typing much more strenuous/irritating -- what is not very
> important in case of advanced development (when time of typing is
> short in relation to time of thinking/reading/testing) but becomes
> quite important in case of scripting (which is still important
> area of Python usage).
If you have a large number of such expressions, what's wrong with this?
FNAME = "full_name" # Define the string in one place only.
current_record[FNAME] == last_record[FNAME] # Use it in many places.
Not only is it shorter to use, but it's easy to change the
key "full_name" to (say) "complete_name" or "volledige_naam" with one
edit, and without mistakenly changing some other string which just
happens to match the key. (I don't know about others, but when I'm
first working on a piece of code, and before I settle on an API or
database schema, I often change field names two or three times before I
settle in on the final version.)
In any case, while I accept that this is sometimes useful, I also think
that it's a something which is simple enough to add to your classes
when necessary with just a few lines -- all you really need are the
__*attr__ methods, everything else is superfluous. If you're doing this
a lot, avoid boilerplate with a class decorator. Here's an untested
minimalistic version which probably does everything necessary:
"""Class decorator which adds attribute access to mappings."""
def __getattr__(self, name):
def __setattr__(self, name, value):
self[name] = value
def __delattr__(self, name):
for func in (__getattr__, __setattr__, __delattr__):
setattr(cls, func.__name__, func)
Fields of an object (attributes) and keys of a mapping are generally for
different purposes, and I'm not sure we should encourage people to
conflate the two. I think this belongs in the cookbook, not the
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