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, 2 insertions, 0 deletions

diff --git a/Library/Formula/google-app-engine.rb b/Library/Formula/google-app-engine.rb
index 6ffb10d1b..fe0e46ecd 100644
--- a/Library/Formula/google-app-engine.rb
+++ b/Library/Formula/google-app-engine.rb
@@ -5,6 +5,8 @@ class GoogleAppEngine < Formula
   url 'http://googleappengine.googlecode.com/files/google_appengine_1.8.0.zip'
   sha1 '71b5f3ee06dce0a7d6af32d65ae27272eac038cb'
 
+  depends_on :python
+
   def install
     cd '..'
     share.install 'google_appengine' => name