[Distutils] [Python-Dev] distlib updated with resources API

Donald Stufft donald.stufft at gmail.com
Mon Oct 1 01:40:51 CEST 2012

On Sunday, September 30, 2012 at 6:50 PM, David Cournapeau wrote:
> I am not sure I understand the argument: whatever the syntax, if the
> feature is there, you will have the same problem ? The fact that it is
> used by existing solutions tend to convince me it is not a problem
> (cabal works much better than distutils/etc... in pretty much every
> way, including installing things with dependency from their package
> servers, not to speak about RPM).

I have a site that pulls data from python packages, one of my problems
of late has been pulling requirements data out of a setuptools setup.py. Simply
fetching the data for my current system is simple, however because of the use
of conditionals that affect the final outcome of the metadata in order to 
make sure I get a true and complete accounting of all the metadata I would
have to anticipate every combination of conditions used inside that file.

Now as far as I can tell, the bento.info conditionals have that same problem
except that they have a much narrow scope, so they have a smaller matrix.

How would I given a package that has an ``if os(windows)`` conditional, get
a representation of that files metadata as if it were in windows? I would need
to override what os(windows) is? Now if this same package also has conditonals
for flags, the matrix becomes larger and larger and I need to either create
my own custom parser that just ignores or annotates the conditionals or I need
to use the official parser and run it through once per item in the matrix to get
the "whole story". Am I incorrect in that?
Additionally, conditionals as they are (to my understanding, having never
used bento but having read the docs and some of it's source code) implemented
in bento complicate the parser and confuse reading a file with understanding
a file.

What additional power or benefit does:

        if os(windows):

provide over:

    "Library": { 
        "InstallRequires": [
            "pywin32; sys.playform == win32"

(Note I dislike the ; <foo> syntax too, but I dislike the conditionals more.)

Maybe i'm missing some powerful construct in the bento.info that warrants
throwing out a lot of hard work and testing of a lot of individuals for these
common formats, however I just don't see it in merely providing a simple
conditional statement. The ``bento.parser`` package contains ~1700 SLOC
now without investigating that terribly deeply I'm willing to bet almost all
of that could be thrown out in the use of a standard format.

I know you've mentioned Cabal a lot when talking about bento, and it's
obvious it's been a very big influence on your design. 
> Conditional markers do make the dependency harder to get right, as
> conditional in dependencies + provides is what makes dependency graph
> building complicated. It seems this can be solved neatly though (see
> http://www.slideshare.net/naderman/dependency-resolution-with-sat-symfony-live-2011-paris).
Good link :)  

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