On Sun, Jul 16, 2006 at 11:52:48PM -0700, Josiah Carlson wrote: > Andrew Bennetts <[EMAIL PROTECTED]> wrote: [...] > > > > Have you seen the "demandload" hack that Mercurial uses? You can find it > > here: > > http://selenic.com/repo/hg?f=cb4715847a81;file=mercurial/demandload.py > > > > You can see an example use of it here: > > http://selenic.com/repo/hg?f=d276571f2c4b;file=mercurial/commands.py > > The problem with that particular method is that it requires that you use > a string to describe the set of modules you would like to import, rather > than a name.
I agree, it's ugly. I'd like there to be a nicer solution. > In the py3k mailing list I recently described a mechanism (though not > implementation) for a somewhat related method to support automatic > reloading when a file has changed (for things like web frameworks), but > by removing that file change check, you get the equivalent to what you > describe, though you don't need to use strings, you can use names... > > from dynamicreload import DR > > and used like... > > DR.os.path.join(...) > > As long as you use the DR.-prefixed name, you get automatic reloading > (if desired) on access. Aside from also being ugly in its own way, a magic prefix like this would add a small performance penalty to places that use it. I believe demandload has the nice feature that once a demandloaded object is accessed, it is replaced with the actual object rather than the demandload gunk, so there's only a one-off performance penalty. > > The advantage for an interactive command line tool isn't so much memory > > consumption as speed. Why waste hundreds of milliseconds importing code > > that > > isn't used? There's an experimental branch to use the same demandload code > > in > > bzr, the reported results are "400ms for 'bzr rocks' down to 100ms, 'bzr > > root' > > from 400ms => 200ms, etc." (according to > > http://permalink.gmane.org/gmane.comp.version-control.bazaar-ng.general/13967) > > > > Over half the runtime wasted on importing unused code! There's a definite > > need > > for a nice solution to this, and it should be included in the standard > > batteries that come with Python. > > Well, just starting up Python without loading any modules can be time > consuming; perhaps even dwarfing the few hundred ms saved by dynamic > loading. Well, it's only about 10ms on my laptop running Ubuntu (it varies up to 90ms, but I expect that's just noise), and the "-S" switch makes no obvious difference (tested with "python -c ''"). 10ms overhead to start python I can live with. It takes about that long run "svn --version". > > If we can address related problems at the same time, like emitting > > deprecation > > warnings for accessing certain module attributes, then even better! > > __deprecated__ = ['name1', ...] > > Make your dynamic load/reload aware of the __deprecated__ attribute, and > you are done. I'm fine with that syntax. But regardless of how it's spelled, I'd really like the standard library or interpreter to have support for it, rather than having a non-standard 3rd-party system for it. I want there to "be one-- and preferably only one --obvious way to do it". -Andrew. _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
