[gentoo-python] [python-r1] Getter functions or 'export' function?

[Michał Górny]

Hello,

Right now, there are two variables which are set per-implementation --
PYTHON & EPYTHON. However, one of our users (sorry for not remembering
who) requested an ability to get Python libdir, site-packages directory
as well. This raises a question on the interface which should be used
to get those values.

The common interface in Gentoo is to use 'getter' functions. Since bash
doesn't have any real concept of return values, those functions use
output capturing -- and that involves subshelling which is pretty bad
for commonly used functions. An alternative is to use an 'export'
function like tc-export() in toolchain-funcs.

I'd like to shortly point out advantages and disadvantages of each
solution.


1) getter functions
   - python_get_PYTHON [<impl>]
   - python_get_EPYTHON <impl>
   - python_get_sitedir [<impl>]

+ clear separation between variables
  -> especially useful to keep docs clear and short

- one subshell (and function call) for each variable, for each
  implementation
  -> that makes it 2 * n-impls for each phase function in distutils-r1


2) a single export function
   - python_export [<impl>] <var>...
   e.g. python_export python2_7 PYTHON EPYTHON PYTHON_SITEDIR

+ no subshelling

+ multiple variables can be set in a single function call

- potential for variable conflicts
  -> e.g. when PYTHON_SITEDIR is used differently by the build system,
     the ebuild would need to 'move' it (unlikely but possible)

- mixing of implementation and variables in parameters (optional first
  parameter)
  -> technically it's acceptable but looks a bit bad.


What are your thoughts?

-- 
Best regards,
Michał Górny