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, 13 insertions, 15 deletions

diff --git a/Library/Formula/py2cairo.rb b/Library/Formula/py2cairo.rb
index eb6fd3487..c9ff3dbc4 100644
--- a/Library/Formula/py2cairo.rb
+++ b/Library/Formula/py2cairo.rb
@@ -8,6 +8,7 @@ class Py2cairo < Formula
   depends_on 'pkg-config' => :build
   depends_on 'cairo'
   depends_on :x11
+  depends_on :python
 
   option :universal
 
@@ -26,23 +27,20 @@ class Py2cairo < Formula
       end
     end
 
-    # waf miscompiles py2cairo on >= lion with HB python, linking the wrong
-    # Python Library.  So add a LINKFLAG that sets the path.
-    # https://github.com/mxcl/homebrew/issues/12893
-    # https://github.com/mxcl/homebrew/issues/14781
-    # https://bugs.freedesktop.org/show_bug.cgi?id=51544
-    ENV['LINKFLAGS'] = "-L#{%x(python-config --prefix).chomp}/lib"
-    system "./waf", "configure", "--prefix=#{prefix}", "--nopyc", "--nopyo"
-    system "./waf", "install"
+    python do
+      # waf miscompiles py2cairo on >= lion with HB python, linking the wrong
+      # Python Library.  So add a LINKFLAG that sets the path.
+      # https://github.com/mxcl/homebrew/issues/12893
+      # https://github.com/mxcl/homebrew/issues/14781
+      # https://bugs.freedesktop.org/show_bug.cgi?id=51544
+      ENV['LINKFLAGS'] = "-L#{python.libdir}"
+      system "./waf", "configure", "--prefix=#{prefix}", "--nopyc", "--nopyo"
+      system "./waf", "install"
+    end
   end
 
-  def caveats; <<-EOS.undent
-    For non-homebrew Python, you need to amend your PYTHONPATH like so:
-      export PYTHONPATH=#{HOMEBREW_PREFIX}/lib/#{which_python}/site-packages:$PYTHONPATH
-    EOS
+  def caveats
+    python.standard_caveats if python
   end
 
-  def which_python
-    "python" + `python -c 'import sys;print(sys.version[:3])'`.strip
-  end
 end