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, 31 insertions, 23 deletions

diff --git a/Library/Formula/libxml2.rb b/Library/Formula/libxml2.rb
index d3d1c1e94..1b0b1b29e 100644
--- a/Library/Formula/libxml2.rb
+++ b/Library/Formula/libxml2.rb
@@ -9,7 +9,8 @@ class Libxml2 < Formula
   keg_only :provided_by_osx
 
   option :universal
-  option 'with-python', 'Compile the libxml2 Python 2.x modules'
+
+  depends_on :python => :recommended
 
   fails_with :llvm do
     build 2326
@@ -26,33 +27,40 @@ class Libxml2 < Formula
     ENV.deparallelize
     system "make install"
 
-    if build.include? 'with-python'
-      # Build Python bindings manually
+    python do
+      # This python do block sets up the site-packages in the Cellar.
       cd 'python' do
-        python_lib = lib/which_python/'site-packages'
-        ENV.append 'PYTHONPATH', python_lib
-        python_lib.mkpath
+        # We need to insert our include dir first
+        inreplace 'setup.py', 'includes_dir = [', "includes_dir = ['#{include}', '#{MacOS.sdk_path}/usr/include',"
+        system python, 'setup.py', "install", "--prefix=#{prefix}"
+      end
+      # This is keg_only but it makes sense to have the python bindings:
+      ohai 'Linking python bindings'
+      Dir["#{python.site_packages}/*"].each{ |f|
+        path = python.global_site_packages/(Pathname.new(f).basename)
+        puts path
+        rm path if path.exist?
+        ln_s f, path
+      }
+    end
 
-        archs = archs_for_command("python")
-        archs.remove_ppc!
-        arch_flags = archs.as_arch_flags
+  end
 
-        ENV.append 'CFLAGS', arch_flags
-        ENV.append 'LDFLAGS', arch_flags
+  def caveats
+    <<-EOS.undent
+      Even if this formula is keg_only, the python bindings have been linked
+      into the global site-packages for your convenience.
+        #{python.global_site_packages}
 
-        unless MacOS::CLT.installed?
-          # We can hijack /opt/include to insert SDKROOT/usr/include
-          inreplace 'setup.py', '"/opt/include",', "'#{MacOS.sdk_path}/usr/include',"
-        end
+      EOS
+  end if build.with? 'python'
 
-        system "python", "setup.py",
-                         "install_lib",
-                         "--install-dir=#{python_lib}"
-      end
+  def test
+    if build.with? 'python'
+      system python, '-c', "import libxml2"
+    else
+      puts "No tests beacuse build --wtihout-python."
+      true
     end
   end
-
-  def which_python
-    "python" + `python -c 'import sys;print(sys.version[:3])'`.strip
-  end
 end