* FixesHomebrew/homebrew#20572 by tweaking the logic that decides
which python is used by the `python` object
inside a formula. There was a bug when on 10.6
there is no Python 2.7 but a :recommended
Python was still treated as being available.
* Use the user's PATH when looking for an external
Python. Until now only brewed or OS X system's
python have been found by `depends_on :python`.
But now we support any Python in PATH (e.g.
pyenv's python).
* Further, instead of handling python modules
and import tests in LanguageModuleDependency,
these are now handled by:
depends_on :python => 'numpy' # for example
The old style
depends_on 'numpy' => :python
is still supported and is only an alias
for the newer style (only for :python, the
other languages are not altered by this commit).
The reasoning is that if a formula requires
a python module, it basically also needs
python itself - and further that specific
version of python has to provide the module.
So the `PythonInstalled` is the natural place
to check for the availability of a python
module.
Using a python module and other tags like
:optional or :recommended is done like so:
depends_on :python => [:optional, 'numpy']
Specifying another PyPi (Python Package index)
name than the module import name is seldom used
but supported, too:
depends_on :python => ['enchant'=>'pyenchant']
A last note: For clarity, you can define
multiple depends_on statements with different
modules to be importable.`
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