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, 11 insertions, 9 deletions

diff --git a/Library/Formula/zookeeper.rb b/Library/Formula/zookeeper.rb
index 78cdfd2b4..b35509a80 100644
--- a/Library/Formula/zookeeper.rb
+++ b/Library/Formula/zookeeper.rb
@@ -7,14 +7,15 @@ class Zookeeper < Formula
 
   head 'http://svn.apache.org/repos/asf/zookeeper/trunk'
 
+  option "c",      "Build C bindings."
+  option "perl",   "Build Perl bindings."
+
   if build.head?
     depends_on :automake
     depends_on :libtool
   end
 
-  option "c",      "Build C bindings."
-  option "perl",   "Build Perl bindings."
-  option "python", "Build Python bindings."
+  depends_on :python => :optional
 
   def shim_script target
     <<-EOS.undent
@@ -59,9 +60,8 @@ class Zookeeper < Formula
       end
     end
 
-    build_python = build.include? "python"
     build_perl = build.include? "perl"
-    build_c = build_python || build_perl || build.include?("c")
+    build_c = build.with?('python') || build_perl || build.include?("c")
 
     # Build & install C libraries.
     cd "src/c" do
@@ -72,10 +72,12 @@ class Zookeeper < Formula
     end if build_c
 
     # Install Python bindings
-    cd "src/contrib/zkpython" do
-      system "python", "src/python/setup.py", "build"
-      system "python", "src/python/setup.py", "install", "--prefix=#{prefix}"
-    end if build_python
+    python do
+      cd "src/contrib/zkpython" do
+        system python, "src/python/setup.py", "build"
+        system python, "src/python/setup.py", "install", "--prefix=#{prefix}"
+      end
+    end
 
     # Install Perl bindings
     cd "src/contrib/zkperl" do