Python dynamic attribute creation
in [Python]
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From: Chris Rebert on 26 Jun 2010 21:35 On Sat, Jun 26, 2010 at 6:06 PM, Steven D'Aprano <steve(a)remove-this-cybersource.com.au> wrote: <snip> > CPython is a fairly plodding implementation. But that's due to the > conservativeness of CPython: Unladen Swallow is faster, and PyPI is > faster still, and the PyPI people expect to eventually be competitive > with C for speed. PyPy (http://pypy.org/), *not* PyPI (http://pypi.python.org/pypi). You're confusing a package index with a self-hosting interpreter; darn typos, eh? Cheers, Chris -- http://blog.rebertia.com
From: Steven D'Aprano on 26 Jun 2010 21:48 On Sat, 26 Jun 2010 18:35:25 -0700, Chris Rebert wrote: > On Sat, Jun 26, 2010 at 6:06 PM, Steven D'Aprano > <steve(a)remove-this-cybersource.com.au> wrote: <snip> >> CPython is a fairly plodding implementation. But that's due to the >> conservativeness of CPython: Unladen Swallow is faster, and PyPI is >> faster still, and the PyPI people expect to eventually be competitive >> with C for speed. > > PyPy (http://pypy.org/), *not* PyPI (http://pypi.python.org/pypi). > You're confusing a package index with a self-hosting interpreter; darn > typos, eh? Damn news client, it should force me to write: set_language_name('PyPy') to catch these sorts of errors and reduce the need for me to proof-read my posts! *wink* -- Steven
From: Carl Banks on 27 Jun 2010 00:01 On Jun 25, 8:24 pm, WANG Cong <xiyou.wangc...(a)gmail.com> wrote: > Understand, but please consider my proposal again, if we switched to: > > setattr(foo, 'new_attr', "blah") > > by default, isn't Python still dynamic as it is? (Please teach me if I > am wrong here.) > > This why I said the questionable thing is not so much related with dynamic > programming or not. Because it makes dynamicism harder to do. Like I said, Python's goal isn't simply to make dynamicism possible, it's to make it easy. "foo.new_attr = 'blah'" is easier than using setattr. Carl Banks
From: Bruno Desthuilliers on 27 Jun 2010 06:35 WANG Cong a écrit : > On 06/25/10 15:34, Bruno Desthuilliers <bruno.42.desthuilliers(a)websiteburo.invalid> wrote: > >> WANG Cong a écrit : >>> Hi, list! >>> >>> I have a doubt about the design of dynamic attribute creation by >>> assignments in Python. >>> >>> As we know, in Python, we are able to create a new attribute of >>> a class dynamically by an assignment: >>> >>>>>> class test: pass >>> ... >>>>>> test.a = "hello" >>>>>> test.a >>> 'hello' >>> >>> However, I still don't get the points why Python designs it like this. >>> >>> My points are: >>> >> (snip) >> >> Python's classes are plain objects, and like any other object are >> created at runtime. Having to special-case them would break the >> simplicity and uniformity of Python for no good reason. Just like >> there's no good reason to make setattr() working differently for class >> and non-class objects. >> > > For implementaiton, perhaps, but not for the language design, how could > a language design be perfect if we can use setattr() like assignments > while use other things, e.g. delattr(), not? Is there any way to express > delattr() as simple as expressing setattr() with assignments? I doubt... cf Ethan's answer on this. > Using assignments to create an attribute hides metaprogramming > while using delattr() exposes it. Once again : in Python, none of this is "metaprogramming" - just plain ordinary programming. So called "metaprogramming" is just an artefact of static languages where datastructures are created at compile time.
From: Bruno Desthuilliers on 27 Jun 2010 06:44
WANG Cong a �crit : (snip) > > The point is why making metaprogramming easy is wonderful? Because it makes life easier ?-) > AND, even if > it were wonderful, why only this one, i.e. creating attributes by > assignments, not other things? Like : class Test(object): a = 1 del Test.a ?-) >>> 2) Metaprogramming should be distinguished with non-meta programming, >>> like templates in C++, it is obvious to see if you are using template >>> metaprogramming in C++. >> Why should it be? > > > It is, if you consider other things of metaprogramming in Python. For > example, deleting an attribute. cf above. >> >>> 3) Thus, allowing dynamic attribute creation by assignment _by default_ >>> is not a good design for me. It is not obvious at all to see if I am >>> doing metaprogramming at a first glance. >> Why do you care if you are doing metaprogramming? Perhaps other languages >> make it seem difficult and scary, but in Python it is not. It is simple >> and easy. >> > > > I do care, programming for a class is quite different from programming > for a non-class, Not when a class is just another ordinary object. |