Python 2.x and 3.x support

New `depends_on :python` Dependency.
New `depends_on :python3` Dependency.

To avoid having multiple formulae with endings -py2 and -py3,
we will handle support for different pythons (2.x vs. 3.x)
in the same formula.
Further brewed vs. external python will be transparently supported.

The formula also gets a new object `python`, which is false if
no Python is available or the user has disabled it. Otherwise
it is defined and provides several support methods:

python.site_packages # the site-packages in the formula's Cellar
python.global_site_packages
python.binary # the full path to the python binary
python.prefix
python.version
python.version.major
python.version.minor
python.xy # => e.g. "python2.7"
python.incdir # includes of python
python.libdir # the python dylib library
python.pkg_config_path # used internally by brew
python.from_osx?
python.framework?
python.universal?
python.pypy?
python.standard_caveats # Text to set PYTHONPATH for python.from_osx?
python.if3then3 # => "" for 2.x and to "3" for 3.x.

Further, to avoid code duplication, `python` takes an optional
block that is run twice if the formula defines depends_on
:python AND :python3.

python do
  system python, 'setup.py', "--prefix=#{prefix}"
end

Read more in the Homebrew wiki.

1 files changed, 4 insertions, 1 deletions

diff --git a/Library/Formula/diffuse.rb b/Library/Formula/diffuse.rb
index 0ae1d474b..bcc889eb4 100644
--- a/Library/Formula/diffuse.rb
+++ b/Library/Formula/diffuse.rb
@@ -5,13 +5,16 @@ class Diffuse < Formula
   url 'http://downloads.sourceforge.net/project/diffuse/diffuse/0.4.7/diffuse-0.4.7.tar.bz2'
   sha1 '9e3b906b579495027b76dc723b5df28e400d3f26'
 
+  depends_on :python
   depends_on 'pygtk'
 
   def install
-    system "python", "./install.py",
+    python do
+      system python, "./install.py",
                      "--sysconfdir=#{etc}",
                      "--examplesdir=#{share}",
                      "--prefix=#{prefix}"
+    end
   end
 
   def test