05-09-2009 Steven D'Aprano <st...@remove-this-cybersource.com.au> wrote:
On Fri, 04 Sep 2009 22:37:15 +0200, Jan Kaliszewski wrote:
Named tuples (which indeed are really very nice) are read-only, but the
approach they represent could (and IMHO should) be extended to some kind
of mutable objects.
[snip]
What sort of extensions did you have in mind?
Two useful (from my point of view) concepts have appeared (or been linked
to) in this thread -- on python-list and python-ideas:
* the namespace/AttrDict concept (see Ken Newton's, Nick Coghlan's and my
posts).
* record concept (see George Sakkis post).
The old discussion, the above link points to, shows that such a
dot-accessible dict-like class is something that many people need and
repeatedly implemet it (more or less perfectly) for themselves.
I think it's something which people copy from other languages because
that's what they're used to, not because they need it.
I don't think so, especially if we say about the former. IMHO it is simply
useful in practice, especially for scripting (but not only) -- being more
convenient than using empty class.
It offers (in compact way, without additional efforts and verbose
syntax -- once you have got such a tool implemented) three things at
the same time, without necessity to choose between them: comfortable
static attribute access, flexible dict-like dynamic access when needed
and possibility of iteration.
It's just a change in syntax. Whether you write x.key or x['key'] is a
matter of convenience. Attribute access is optimized for when you know
the key names at compile time, key access is optimized for when you don't
know the names until runtime.
Exactly. It is a matter of *convenience* (as well as large areas of Python)
and that's the point. I suppose that that is the reason for people to
repeatedly implement it for themselves.
05-09-2009 Steven D'Aprano <st...@remove-this-cybersource.com.au> wrote:
On Fri, 04 Sep 2009 22:51:39 -0700, Ken Newton wrote:
[snip]
I would think this is much more than just copy from other language
styles or 'just' a syntax change -- the apparent widespread use would
hint at a deeper need.
"Apparent" is the key word there. There are lots of people who *say* this
this useful functionality, but how many of them *actually* use it? And of
those who do use it, how many of them know what they're doing? There are
an awful lot of bad programmers out there.
If you do need such functionality, it's easy to implement. Here's one:
Neither you nor me have hard evidence about popularity/unpopularity of the
idea (number of places where you can find similar, more or less successful,
attempts to implement it seems to testify in favour of the idea) -- nor
about how it is used or abused.
Obviously there are a lot of bad programmers who are able to use globals
instead of function arguments etc.... Thats the fate of every language
feature.
But it's not the reason to resign from a feature that has particular common
and proper use-cases. Even official Python tutorial mentions a case that is
typical for the matter:
http://docs.python.org/3.1/tutorial/classes.html#odds-and-ends
As a
general rule, if obj.x is an attribute, then every valid obj should have
an attribute x. But if obj['x'] is a key/value, then it is data-specific:
some instances will have an 'x' key, and some won't.
It's often true but not always (see e.g. the above example in docs).
Cheers,
*j
--
Jan Kaliszewski (zuo) <z...@chopin.edu.pl>
--
http://mail.python.org/mailman/listinfo/python-list
