[Distutils] [RFC] support configure + make pattern in distutils (or setuptools)

[Manlio Perillo]

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Hi.

Recently I have started a new project that needs some runtime configuration.

All the open sources projects I have reviewed, do the configuration step
by usually deriving from the build_ext command class, and then execute
some configuration code to set required options.

This result in what I believe is bad design, and in some cases the
setup.py ends up in a unreadable mess of code.

I think that the setup.py should be as much as declarative as possible.


I have studied the distutils source code, where I found a config command.
Unfortunately this command is never used by other commands, e.g., the
build_ext does not call self.set_undefined_options('config', ...)

Another problem is that you have to do something like this:

    $ python setup.py \
      config --pg_config=/usr/local/pgsql/bin/pg_config \
      build

every time you need to build code (e.g. during development).


This is the reason a decided to write an "improved" config command; I
have attached a sample implementation.

The new config command does the following:

If config.dat (adjacent to setup.py file) does not exists, or if user
has explicitly executed the config command or if setup.cfg is
newer than config.dat, then:

  call the configure method (that user must override), and then save
  all options to config.dat file, using pickle
  (XXX the code here is a bit tricky [1])

otherwise, load the config.dat file and set options in the config
command instace.


This implementation allow users to use the traditional configure + make
pattern:

    $ python setup.py config --pg_config=/usr/local/pgsql/bin/pg_config
    $ python setup.py build
    $ sudo python setup.py install (or develop, using setuptools)


A project that needs runtime configuration, will create a config.py
module (adjacent to setup.py) file, and will define a custom config
command, derived from the provided class.

The setup.py file will import the config module, and will use the
cmdclass setup option to register the new command.


The next step is to implement an "improved" build_ext command, that will
use options from the config command, as default values.


[1] a better solution is to have the configure method return a
    dictionary, but it is more verbose



Feedback is appreciated.



Thanks   Manlio Perillo
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