[Python-Dev] First draft of "sysconfig"

[Brett Cannon]

On Sat, Dec 12, 2009 at 12:02, Tarek Ziadé <ziade.tarek at gmail.com> wrote:

> Hello,
>
> A while ago I've proposed to refactor the APIs that provides access to
> the installation paths and configuration variables at runtime into a
> single module called "sysconfig", and make it easier for all
> implementations to work with them.
>
> I've started a branch and worked on it, and I'd like to ask here for
> some feedback. And in particular from Jython and IronPython people
> because they would probably need to work in that file for their
> implementation and/or propose things to add. My understanding is that
> we have people like Phillip (Jenvey), Michael F., Frank W. in this
> list so they can comment directly and I don't need to cross-post this
> mail elsewhere.
>
> == Installation schemes ==
>
> First, the module contains the installation schemes for each platform
> CPython uses.
> An install scheme is a mapping where the key is the "code" name for a
> directory, and
> the value the path of that directory, with some $variable that can be
> expanded.
>
> Install schemes are stored in a private mapping, where the keys are
> usually the value of os.name,
> and the value, the mapping I've mentionned earlier.
>
> So, for example, the paths for win32 are:
>
> _INSTALL_SCHEMES = {
>  ...
>  'nt': {
>        'stdlib': '$base/Lib',
>        'platstdlib': '$base/Lib',
>        'purelib': '$base/Lib/site-packages',
>        'platlib': '$base/Lib/site-packages',
>        'include': '$base/include',
>        'platinclude': '$base/include',
>        'scripts': '$base/Scripts',
>        'data'   : '$base',
>        },
>  ...
> }
>
>
Are you using string.Template because this code needs to run on installs
older than 2.6?

-Brett




> where each key corresponds to a directory that contains some Python files:
>
> - stdlib : root of the standard library
> - platstdlib: root of platform-specific elements of the standard library
> - purelib: the site-packages directory for pure python modules
> - platlib: the site-packages directory for platform-specific modules
> - include: the include dir
> - platinclude: the include dir for platform-specific files
> - scripts: the directory where scripts are added
> - data: the directory where data file are added
>
> All these directory are read and used by:
> - distutils when a package is installed, so the install command can
> dispatch files in the right place
> - site.py, when Python is initialized
>
> IOW, any part of the stdlib can use these paths to locate and work
> with Python files.
>
> The public APIs are:
>
> * get_path_names() : returns a list of the path names ("stdlib",
> "platstdlib", etc.)
>
> * get_paths(scheme, vars)  : Returns a mapping containing an install
> scheme.
>   - "scheme" is the name of the scheme, if not provided will get the
> default scheme of the current platform
>   - vars is an optonal mapping that can provide values for the
> various $variables. Notice that they all have
>      default values, for example $base == sys.prefix.
>
>    for example: get_paths('nt')
>
> * get_path(name, scheme, vars): Returns one path corresponding to the
> scheme.
>
>  for example : get_paths('stdlib', 'nt')
>
> Those API are generic, but maybe we could add specific APIs like:
>
> * get_stdlib_path('nt')
>
> These API are basically a refactoring of what already exist in
> distutils/command/install.py
>
> == Configuration variables ==
>
> distutils.sysconfig currently provides some APIs to read values from
> files like Makefile and pyconfig.h.
>
> These API have been placed in the global sysconfig module:
>
> * get_config_vars(): return a dictionary of all configuration
> variables relevant for the current platform.
>
> * get_config_var(name): Return the value of a single variable
>
> * get_platform():  Return a string that identifies the current
> platform. (this one is used by site.py for example)
>
> * get_python_version() : return the short python version
> (sys.version[:3]) -- this one could probably go away but is useful
> because that's the marker used by Python in some paths.
>
> == code, status, next steps ==
>
> The code of the module can be viewed here, it's a revamp of
> distutils.sysconfig:
>
>
> http://svn.python.org/view/*checkout*/python/branches/tarek_sysconfig/Lib/sysconfig.py?content-type=text%2Fplain
>
> I've refactored distutils/ and site.py so they work with this new
> module, and added deprecation warnings in distutils.sysconfig.
>
> All tests pass in the branch, but note that the code is still using
> the .h and Makefile files. This will probably be removed later in
> favor of a static _sysconfig.py file generated when Python is built,
> containing the variables sysconfig reads. I'll do this second step
> after I get some feedback on the proposal.
>
> Regards
> Tarek
>
> --
> Tarek Ziadé | http://ziade.org
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