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.

15 files changed, 511 insertions, 25 deletions

diff --git a/Library/Homebrew/build_options.rb b/Library/Homebrew/build_options.rb
index 24c49931f..077a8b3d8 100644
--- a/Library/Homebrew/build_options.rb
+++ b/Library/Homebrew/build_options.rb
@@ -85,4 +85,19 @@ class BuildOptions
   def unused_options
     Options.new(@options - @args)
   end
+
+  # Some options are implicitly ON because they are not explictly turned off
+  # by their counterpart option. This applies only to with-/without- options.
+  # implicit_options are needed because `depends_on 'spam' => 'with-stuff'`
+  # complains if 'spam' has stuff as default and only defines `--without-stuff`.
+  def implicit_options
+    implicit = unused_options.map do |o|
+      if o.name =~ /^with-(.+)$/ && without?($1)
+        Option.new("without-#{$1}")  # we loose the description, but that's ok
+      elsif o.name =~ /^without-(.+)$/ && with?($1)
+        Option.new("with-#{$1}")
+      end
+    end.compact
+    Options.new(implicit)
+  end
 end
diff --git a/Library/Homebrew/cmd/audit.rb b/Library/Homebrew/cmd/audit.rb
index 6bab71095..99aad1392 100644
--- a/Library/Homebrew/cmd/audit.rb
+++ b/Library/Homebrew/cmd/audit.rb
@@ -148,11 +148,18 @@ class FormulaAuditor
         problem <<-EOS.undent unless dep.tags.any? || f.name =~ /automake/ && dep.name == 'autoconf'
         #{dep} dependency should be "depends_on '#{dep}' => :build"
         EOS
-      when "git", "python", "ruby", "emacs", "mysql", "mercurial"
+      when "git", "ruby", "emacs", "mysql", "mercurial"
         problem <<-EOS.undent
           Don't use #{dep} as a dependency. We allow non-Homebrew
           #{dep} installations.
           EOS
+      when 'python', 'python2', 'python3'
+        problem <<-EOS.undent
+          Don't use #{dep} as a dependency (string).
+             We have special `depends_on :python` (or :python2 or :python3 )
+             that works with brewed and system Python and allows us to support
+             bindings for 2.x and 3.x in parallel and much more.
+          EOS
       when "postgresql"
         # Postgis specifically requires a Homebrewed postgresql
         unless f.name == "postgis"
@@ -232,7 +239,7 @@ class FormulaAuditor
       end
 
       if p =~ %r[^http://prdownloads\.]
-        problem "Don't use prdownloads in SourceForge urls (url is #{p}).\n" + 
+        problem "Don't use prdownloads in SourceForge urls (url is #{p}).\n" +
                 "\tSee: http://librelist.com/browser/homebrew/2011/1/12/prdownloads-is-bad/"
       end
 
@@ -249,7 +256,7 @@ class FormulaAuditor
     # Check for http:// GitHub repo urls, https:// is preferred.
     urls.grep(%r[^http://github\.com/.*\.git$]) do |u|
       problem "Use https:// URLs for accessing GitHub repositories (url is #{u})."
-    end 
+    end
 
     # Use new-style archive downloads
     urls.select { |u| u =~ %r[https://.*/(?:tar|zip)ball/] and not u =~ %r[\.git$] }.each do |u|
@@ -427,6 +434,14 @@ class FormulaAuditor
       problem "Reference '#{$1}' without dashes"
     end
 
+    if text =~ /build\.with\?\s+['"]-?-?with-(.*)['"]/
+      problem "No double 'with': Use `build.with? '#{$1}'` to check for \"--with-#{$1}\""
+    end
+
+    if text =~ /build\.without\?\s+['"]-?-?without-(.*)['"]/
+      problem "No double 'without': Use `build.without? '#{$1}'` to check for \"--without-#{$1}\""
+    end
+
     if text =~ /ARGV\.(?!(debug\?|verbose\?|find[\(\s]))/
       problem "Use build instead of ARGV to check options"
     end
@@ -457,6 +472,52 @@ class FormulaAuditor
     end
   end
 
+  def audit_python
+    if text =~ /system\(?\s*['"]python/
+      # Todo: In `def test` it is okay to do it this way. It's even recommended!
+      problem "Instead of `system 'python', ...`, call `system python, ...`."
+    end
+
+    if text =~ /system\(?\s*python\.binary/
+      problem "Instead of `system python.binary, ...`, call `system python, ...`."
+    end
+
+    if text =~ /(def\s*)?which_python/
+      problem "Replace `which_python` by `python.xy`, which returns e.g. 'python2.7'."
+    end
+
+    if text =~ /which\(?["']python/
+      problem "Don't locate python with `which 'python'`, use `python.binary` instead"
+    end
+
+    if f.requirements.any?{ |r| r.kind_of?(PythonInstalled) }
+      # Don't check this for all formulae, because some are allowed to set the
+      # PYTHONPATH. E.g. python.rb itself needs to set it.
+      if text =~ /ENV\.append.*PYTHONPATH/ || text =~ /ENV\[['"]PYTHONPATH['"]\]\s*=[^=]/
+        problem "Don't set the PYTHONPATH, instead declare `depends_on :python`."
+      end
+    end
+
+    if text =~ /(\s*)def\s+caveats((.*\n)*?)(\1end)/ || /(\s*)def\s+caveats;(.*?)end/
+      caveats_body = $2
+        if caveats_body =~ /(python[23]?)\.(.*\w)/
+          # So if in the body of caveats there is a `python.whatever` called,
+          # check that there is a guard like `if python` or similiar:
+          python = $1
+          method = $2
+          unless caveats_body =~ /(if python[23]?)|(if build\.with\?\s?\(?['"]python)|(unless build.without\?\s?\(?['"]python)/
+          problem "Please guard `#{python}.#{method}` like so `#{python}.#{method} if #{python}`"
+        end
+      end
+    end
+
+    # Todo:
+    # The python do ... end block is possibly executed twice. Once for
+    # python 2.x and once for 3.x. So if a `system 'make'` is called, a
+    # `system 'make clean'` should also be called at the end of the block.
+
+  end
+
   def audit
     audit_file
     audit_specs
@@ -465,6 +526,7 @@ class FormulaAuditor
     audit_conflicts
     audit_patches
     audit_text
+    audit_python
   end
 
   private
diff --git a/Library/Homebrew/dependency.rb b/Library/Homebrew/dependency.rb
index cc378b7df..a6905bc37 100644
--- a/Library/Homebrew/dependency.rb
+++ b/Library/Homebrew/dependency.rb
@@ -47,7 +47,7 @@ class Dependency
   end
 
   def missing_options
-    options - Tab.for_formula(to_formula).used_options
+    options - Tab.for_formula(to_formula).used_options - to_formula.build.implicit_options
   end
 
   def universal!
diff --git a/Library/Homebrew/dependency_collector.rb b/Library/Homebrew/dependency_collector.rb
index 3de385fbf..74f94dc63 100644
--- a/Library/Homebrew/dependency_collector.rb
+++ b/Library/Homebrew/dependency_collector.rb
@@ -17,7 +17,7 @@ require 'set'
 class DependencyCollector
   # Define the languages that we can handle as external dependencies.
   LANGUAGE_MODULES = Set[
-    :chicken, :jruby, :lua, :node, :ocaml, :perl, :python, :rbx, :ruby
+    :chicken, :jruby, :lua, :node, :ocaml, :perl, :python, :python2, :python3, :rbx, :ruby
   ].freeze
 
   attr_reader :deps, :requirements
@@ -92,6 +92,9 @@ class DependencyCollector
     when :clt        then CLTDependency.new(tags)
     when :arch       then ArchRequirement.new(tags)
     when :hg         then MercurialDependency.new(tags)
+    when :python     then PythonInstalled.new(tags)
+    when :python2    then PythonInstalled.new("2", tags)
+    when :python3    then PythonInstalled.new("3", tags)
     else
       raise "Unsupported special dependency #{spec}"
     end
diff --git a/Library/Homebrew/download_strategy.rb b/Library/Homebrew/download_strategy.rb
index 6745219fb..72a0652fb 100644
--- a/Library/Homebrew/download_strategy.rb
+++ b/Library/Homebrew/download_strategy.rb
@@ -548,6 +548,7 @@ class MercurialDownloadStrategy < AbstractDownloadStrategy
   def cached_location; @clone; end
 
   def hgpath
+    # #{HOMEBREW_PREFIX}/share/python/hg is deprecated, but we levae it in for a while
     @path ||= %W[
       #{which("hg")}
       #{HOMEBREW_PREFIX}/bin/hg
diff --git a/Library/Homebrew/formula.rb b/Library/Homebrew/formula.rb
index dab9726ed..bf64044b3 100644
--- a/Library/Homebrew/formula.rb
+++ b/Library/Homebrew/formula.rb
@@ -305,6 +305,21 @@ class Formula
     ]
   end
 
+  def python(options={:allowed_major_versions => [2, 3]}, &block)
+    require 'python_helper'
+    self.instance_eval{ python_helper(options, &block) }
+  end
+
+  # Explicitly only execute the block for 2.x (if a python 2.x is available)
+  def python2 &block
+    python(:allowed_major_versions => [2], &block)
+  end
+
+  # Explicitly only execute the block for 3.x (if a python 3.x is available)
+  def python3 &block
+    python(:allowed_major_versions => [3], &block)
+  end
+
   def self.class_s name
     # remove invalid characters and then camelcase it
     name.capitalize.gsub(/[-_.\s]([a-zA-Z0-9])/) { $1.upcase } \
@@ -558,7 +573,7 @@ class Formula
       @exec_count ||= 0
       @exec_count += 1
       logd = HOMEBREW_LOGS/name
-      logfn = "#{logd}/%02d.%s" % [@exec_count, File.basename(cmd).split(' ').first]
+      logfn = "#{logd}/%02d.%s" % [@exec_count, File.basename(cmd.to_s).split(' ').first]
       mkdir_p(logd)
 
       rd, wr = IO.pipe
@@ -567,7 +582,7 @@ class Formula
         $stdout.reopen wr
         $stderr.reopen wr
         args.collect!{|arg| arg.to_s}
-        exec(cmd, *args) rescue nil
+        exec(cmd.to_s, *args) rescue nil
         puts "Failed to execute: #{cmd}"
         exit! 1 # never gets here unless exec threw or failed
       end
diff --git a/Library/Homebrew/keg.rb b/Library/Homebrew/keg.rb
index a63af419d..e1df0adb5 100644
--- a/Library/Homebrew/keg.rb
+++ b/Library/Homebrew/keg.rb
@@ -210,15 +210,18 @@ class Keg < Pathname
   def link_dir foo, mode=OpenStruct.new
     root = self+foo
     return unless root.exist?
-
     root.find do |src|
       next if src == root
-
       dst = HOMEBREW_PREFIX+src.relative_path_from(self)
       dst.extend ObserverPathnameExtension
 
       if src.file?
         Find.prune if File.basename(src) == '.DS_Store'
+        # Don't link pyc files because Python overwrites these cached object
+        # files and next time brew wants to link, the pyc file is in the way.
+        if src.extname.to_s == '.pyc' && src.to_s =~ /site-packages/
+          Find.prune
+        end
 
         case yield src.relative_path_from(root)
         when :skip_file, nil
@@ -233,7 +236,6 @@ class Keg < Pathname
       elsif src.directory?
         # if the dst dir already exists, then great! walk the rest of the tree tho
         next if dst.directory? and not dst.symlink?
-
         # no need to put .app bundles in the path, the user can just use
         # spotlight, or the open command and actual mac apps use an equivalent
         Find.prune if src.extname.to_s == '.app'
diff --git a/Library/Homebrew/python_helper.rb b/Library/Homebrew/python_helper.rb
new file mode 100644
index 000000000..ef71b2a30
--- /dev/null
+++ b/Library/Homebrew/python_helper.rb
@@ -0,0 +1,80 @@
+
+# The python_helper is used in the Formula class when the user calls
+# `python`, `python2` or `python3`.
+
+# This method has a dual nature. For one, it takes a &block and sets up
+# the ENV such that a Python, as defined in the requirements, is the default.
+# If there are multiple `PythonInstalled` requirements, the block is evaluated
+# once for each Python. This makes it possible to easily support 2.x and
+# 3.x Python bindings without code duplication in formulae.
+# If you need to special case stuff, set :allowed_major_versions.
+# Second, inside the block, a formula author may call this method to access
+# certain convienience methods for the currently selected Python, e.g.
+# `python.site_packages`.
+def python_helper(options={:allowed_major_versions => [2, 3]}, &block)
+  if !block_given? and !@current_python.nil?
+    # We are already inside of a `python do ... end` block, so just return
+    # the current_python or false if the version.major is not allowed.
+    if options[:allowed_major_versions].include?(@current_python.version.major)
+      @current_python
+    else
+      false
+    end
+  else
+    # Look for PythonInstalled requirements for this formula
+    python_reqs = requirements.select{ |r| r.kind_of?(PythonInstalled) }
+    if python_reqs.empty?
+      raise "If you use python in the formula, you have to add `depends_on :python` (or :python3)!"
+    end
+    # Now select those that are satisfied and matching the version.major
+    python_reqs = python_reqs.select do |p|
+      p.satisfied? &&
+      options[:allowed_major_versions].include?(p.version.major) &&
+      if p.optional? || p.recommended?
+        self.build.with?(p.name)
+      else
+        true
+      end
+    end
+
+    # Allow to use an else-branch like so: `if python do ... end; else ... end`
+    return false if python_reqs.empty?
+
+    # Sort by version, so the older 2.x will be used first and if no
+    # block_given? then 2.x is preferred because it is returned.
+    # Further note, having 3.x last allows us to run `2to3 --write .`
+    # which modifies the sources in-place (for some packages that need this).
+    python_reqs.sort_by{ |py| py.version }.map do |py|
+      # Now is the time to set the site_packages to the correct value
+      py.site_packages = lib/py.xy/'site-packages'
+      if block_given?
+        puts "brew: Python block (#{py.binary})..." if ARGV.verbose?
+        require 'superenv'
+        # Ensure env changes are only temporary by using `with_build_environment`
+        ENV.with_build_environment do
+          # In order to install into the Cellar, the dir must exist and be in the
+          # PYTHONPATH. This will be executed in the context of the formula
+          # so that lib points to the HOMEBREW_PREFIX/Cellar/<formula>/<version>/lib
+          puts "brew: Setting PYTHONPATH=#{py.site_packages}" if ARGV.verbose?
+          mkdir_p py.site_packages
+          ENV.append 'PYTHONPATH', py.site_packages, ':'
+          ENV['PYTHON'] = py.binary
+          ENV.prepend 'CMAKE_INCLUDE_PATH', py.incdir, ':'
+          ENV.prepend 'PKG_CONFIG_PATH', py.pkg_config_path, ':' if py.pkg_config_path
+          ENV.prepend 'PATH', py.binary.dirname, ':' unless py.from_osx?
+          # Track the state of the currently selected python for this block,
+          # so if this python_helper is called again _inside_ the block, we can
+          # just return the right python (see `else`-branch a few lines down):
+          @current_python = py
+          res = instance_eval(&block)
+          @current_python = nil
+          res
+        end
+      else
+        puts "brew: Using #{py.binary}" if ARGV.verbose?
+        # We return here with intention, because no block_given?
+        return py
+      end
+    end
+  end
+end
diff --git a/Library/Homebrew/requirements.rb b/Library/Homebrew/requirements.rb
index ad621867c..c1c7fff7a 100644
--- a/Library/Homebrew/requirements.rb
+++ b/Library/Homebrew/requirements.rb
@@ -3,6 +3,7 @@ require 'requirements/conflict_requirement'
 require 'requirements/language_module_dependency'
 require 'requirements/x11_dependency'
 require 'requirements/mpi_dependency'
+require 'requirements/python_dependency'
 
 class XcodeDependency < Requirement
   fatal true
diff --git a/Library/Homebrew/requirements/language_module_dependency.rb b/Library/Homebrew/requirements/language_module_dependency.rb
index 7c293e0c5..e62e61530 100644
--- a/Library/Homebrew/requirements/language_module_dependency.rb
+++ b/Library/Homebrew/requirements/language_module_dependency.rb
@@ -27,7 +27,8 @@ class LanguageModuleDependency < Requirement
       when :node then %W{/usr/bin/env node -e require('#{@import_name}');}
       when :ocaml then %W{/usr/bin/env opam list #{@import_name} | grep #{@import_name}}
       when :perl then %W{/usr/bin/env perl -e use\ #{@import_name}}
-      when :python then %W{/usr/bin/env python -c import\ #{@import_name}}
+      when :python then %W{/usr/bin/env python2 -c import\ #{@import_name}}
+      when :python3 then %W{/usr/bin/env python3 -c import\ #{@import_name}}
       when :ruby then %W{/usr/bin/env ruby -rubygems -e require\ '#{@import_name}'}
       when :rbx then %W{/usr/bin/env rbx -rubygems -e require\ '#{@import_name}'}
     end
@@ -42,6 +43,7 @@ class LanguageModuleDependency < Requirement
       when :ocaml   then "opam install"
       when :perl    then "cpan -i"
       when :python  then "pip install"
+      when :python3 then "pip3 install"
       when :rbx     then "rbx gem install"
       when :ruby    then "gem install"
     end
diff --git a/Library/Homebrew/requirements/python_dependency.rb b/Library/Homebrew/requirements/python_dependency.rb
new file mode 100644
index 000000000..194d434c7
--- /dev/null
+++ b/Library/Homebrew/requirements/python_dependency.rb
@@ -0,0 +1,296 @@
+require 'requirement'
+
+# We support Python 2.x and 3.x, either brewed or external.
+# This requirement locates the correct CPython binary (no PyPy), provides
+# support methods like `site_packages`, and writes our sitecustomize.py file.
+# In `dependency_collector.rb`, special `:python` and `:python3` shortcuts are
+# defined. You can specify a minimum version of the Python that needs to be
+# present, but since not every package is ported to 3.x yet,
+# `PythonInstalled("2")` is not satisfied by 3.x.
+# In a formula that shall provide support for 2.x and 3.x, the idiom is:
+# depends_on :python
+# depends_on :python3 => :optional # or :recommended
+#
+# Todo:
+# - Allow further options that choose: universal, framework?, brewed?...
+class PythonInstalled < Requirement
+  attr_reader :min_version
+  attr_reader :if3then3
+  attr_reader :site_packages
+  attr_accessor :site_packages
+
+  fatal true  # you can still make Python optional by `depends_on :python => :optional`
+
+  class PythonVersion < Version
+    def major
+      to_a[0].to_s.to_i  # Python's major.minor are always ints.
+    end
+    def minor
+      to_a[1].to_s.to_i
+    end
+  end
+
+  def initialize(*tags)
+    # Extract the min_version if given. Default to python 2.X else
+    tags.flatten!
+    if /(\d+\.)*\d+/ === tags.first
+      @min_version = PythonVersion.new(tags.shift)
+    else
+      @min_version = PythonVersion.new("2.7")  # default
+    end
+
+    # often used idiom: e.g. sipdir = "share/sip" + python.if3then3
+    if @min_version.major == 3
+      @if3then3 = "3"
+    else
+      @if3then3 = ""
+    end
+
+    # Set name according to the major version.
+    # The name is used to generate the options like --without-python3
+    @name = "python" + @if3then3
+
+    # will be set later by the python_helper, because it needs the
+    # formula prefix to set site_packages
+    @site_packages = nil
+
+    super tags
+  end
+
+  # Note that during `satisfy` we still have the PATH as the user has set.
+  # We look for a brewed python or an external Python and store the loc of
+  # that binary for later usage. (See Formula#python)
+  satisfy :build_env => false do
+    @unsatisfied_because = "This formula needs #{@name}.\n"
+    if binary.nil?
+      @unsatisfied_because += "But no `#{@name}` found in your PATH! Consider to `brew install #{@name}`."
+      false
+    elsif pypy?
+      @unsatisfied_because += "Your #{@name} executable appears to be a PyPy, which is not supported."
+      false
+    elsif version.major != @min_version.major
+      @unsatisfied_because += "No Python #{@min_version.major}.x found!"
+      false
+    elsif version < @min_version
+      @unsatisfied_because += "Python version #{version} is too old (need at least #{@min_version})."
+      false
+    elsif @min_version.major == 2 && `python -c "import sys; print(sys.version_info.major)"`.strip == "3"
+      @unsatisfied_because += "Your `python` points to a Python 3.x. This is not supported."
+      false
+    else
+      true
+    end
+  end
+
+  # The full path to the python or python3 executable, depending on `version`.
+  def binary
+    if brewed?
+      # If the python is brewed we always prefer it!
+      # Note, we don't support homebrew/versions/pythonXX.rb, though.
+      Formula.factory(@name).opt_prefix/"bin/python#{@min_version.major}"
+    else
+      p = which(@name)
+      raise "PythonInstalled: #{p} is not executable" if !p.nil? && !p.executable?
+      p
+    end
+  end
+
+  # The python prefix (special cased for a brewed python to point into the opt_prefix)
+  def prefix
+    if brewed?
+      # Homebrew since a long while only supports frameworked python
+      HOMEBREW_PREFIX/"opt/#{name}/Frameworks/Python.framework/Versions/#{version.major}.#{version.minor}"
+    elsif from_osx?
+      # Python on OS X has been stripped off its includes (unless you install the CLT), therefore we use the MacOS.sdk.
+      Pathname.new("#{MacOS.sdk_path}/System/Library/Frameworks/Python.framework/Versions/#{version.major}.#{version.minor}")
+    else
+      # What Python knows about itself
+      Pathname.new(`#{binary} -c 'import sys;print(sys.prefix)'`.strip)
+    end
+  end
+
+  # Get the actual x.y.z version by asking python (or python3 if @min_version>=3)
+  def version
+    @version ||= PythonVersion.new(`#{binary} -c 'import sys;print(sys.version[:5])'`.strip)
+  end
+
+  # python.xy => "python2.7" is often used (and many formulae had this as `which_python`).
+  def xy
+    "python#{version.major}.#{version.minor}"
+  end
+
+  # Homebrew's global site-packages. The local ones are populated by the
+  # python_helper method when the `prefix` of a formula is known.
+  def global_site_packages
+    HOMEBREW_PREFIX/"lib/#{xy}/site-packages"
+  end
+
+  # Dir containing Python.h and others.
+  def incdir
+    if (from_osx? || brewed?) && framework?
+      prefix/"Headers"
+    else
+      # For all other we use Python's own standard method (works with a non-framework version, too)
+      Pathname.new(`#{binary} -c 'from distutils import sysconfig; print(sysconfig.get_python_inc())'`.strip)
+    end
+  end
+
+  # Dir containing e.g. libpython2.7.dylib
+  def libdir
+    if brewed? || from_osx?
+      prefix/"lib/#{xy}/config"
+    else
+      Pathname.new(`#{binary} -c "from distutils import sysconfig; print(sysconfig.get_config_var('LIBPL'))"`.strip)
+    end
+  end
+
+  # Pkgconfig (pc) files of python
+  def pkg_config_path
+    if from_osx?
+      # No matter if CLT-only or Xcode-only, the pc file is always here on OS X:
+      path = Pathname.new("/System/Library/Frameworks/Python.framework/Versions/#{version.major}.#{version.minor}/lib/pkgconfig")
+      path if path.exist?
+    else
+      prefix/"lib/pkgconfig"
+    end
+  end
+
+  # Is the Python brewed (and linked)?
+  def brewed?
+    @brewed ||= begin
+      require 'formula'
+      f = Formula.factory(@name)
+      f.installed? && f.linked_keg.exist?
+    end
+  end
+
+  # Is the python the one from OS X?
+  def from_osx?
+    @from_osx ||= begin
+      p = `#{binary} -c "import sys; print(sys.prefix)"`.strip
+      p.start_with?("/System/Library/Frameworks/Python.framework")
+    end
+  end
+
+  # Is the `python` a PyPy?
+  def pypy?
+    @pypy ||= !(`#{binary} -c "import sys; print(sys.version)"`.downcase =~ /.*pypy.*/).nil?
+  end
+
+  # Is this python a framework-style install (OS X only)?
+  def framework?
+    @framework ||= /Python[0-9]*\.framework/ === prefix.to_s
+  end
+
+  def universal?
+    @universal ||= archs_for_command(binary).universal?
+  end
+
+  def standard_caveats
+    if brewed?
+      ""  # empty string, so we can concat this
+    else
+      <<-EOS.undent
+        For non-homebrew #{@name} (#{@min_version.major}.x), you need to amend your PYTHONPATH like so:
+          export PYTHONPATH=#{global_site_packages}:$PYTHONPATH
+      EOS
+    end
+  end
+
+  def modify_build_environment
+    # Write our sitecustomize.py
+    file = global_site_packages/"sitecustomize.py"
+    ohai "Writing #{file}" if ARGV.verbose? || ARGV.homebrew_developer?
+    [".pyc", ".pyo", ".py"].map{ |f|
+      global_site_packages/"sitecustomize#{f}"
+    }.each{ |f| f.delete if f.exist? }
+    file.write(sitecustomize)
+
+    # For non-system python's we add the opt_prefix/bin of python to the path.
+    ENV.prepend 'PATH', binary.dirname, ':' unless from_osx?
+
+    ENV['PYTHONHOME'] = nil  # to avoid fuck-ups.
+    ENV['PYTHONNOUSERSITE'] = '1'
+    # Python respects the ARCHFLAGS var if set. Shall we set them here?
+    # ENV['ARCHFLAGS'] = ??? # FIXME
+    ENV.append 'CMAKE_INCLUDE_PATH', incdir, ':'
+    ENV.append 'PKG_CONFIG_PATH', pkg_config_path, ':' if pkg_config_path
+
+    # Udpate distutils.cfg (later we can remove this, but people still have
+    # their old brewed pythons and we have to update it here)
+    # Todo: If Jack's formula revisions arrive, we can get rid of this here!
+    if brewed?
+      require 'formula'
+      file = Formula.factory(@name).prefix/"Frameworks/Python.framework/Versions/#{version.major}.#{version.minor}/lib/#{xy}/distutils/distutils.cfg"
+      ohai "Writing #{file}" if ARGV.verbose? || ARGV.homebrew_developer?
+      file.delete if file.exist?
+      file.write <<-EOF.undent
+        [global]
+        verbose=1
+        [install]
+        force=1
+        prefix=#{HOMEBREW_PREFIX}
+      EOF
+    end
+  end
+
+  def sitecustomize
+    <<-EOF.undent
+      # This file is created by Homebrew and is executed on each python startup.
+      # Don't print from here, or else universe will collapse.
+      import sys
+
+      if sys.version_info.major == #{version.major} and sys.version_info.minor == #{version.minor}:
+          if sys.executable.startswith('#{HOMEBREW_PREFIX}'):
+              # Fix 1)
+              #   A setuptools.pth and/or easy-install.pth sitting either in
+              #   /Library/Python/2.7/site-packages or in
+              #   ~/Library/Python/2.7/site-packages can inject the
+              #   /System's Python site-packages. People then report
+              #   "OSError: [Errno 13] Permission denied" because pip/easy_install
+              #   attempts to install into
+              #   /System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python
+              #   See: https://github.com/mxcl/homebrew/issues/14712
+              # Fix 2)
+              #   Remove brewed Python's hard-coded Cellar-site-packages
+              sys.path = [ p for p in sys.path
+                           if not (p.startswith('/System') or
+                                   p.startswith('#{HOMEBREW_PREFIX}/Cellar/python') and p.endswith('site-packages')) ]
+              # Fix 3)
+              # Set the sys.executable to use the opt_prefix
+              sys.executable = '#{HOMEBREW_PREFIX}/opt/#{name}/bin/python#{version.major}.#{version.minor}'
+              # Fix 4)
+              # Make LINKFORSHARED (and python-confing --ldflags) return the
+              # full path to the lib (yes, "Python" is actually the lib, not a
+              # dir) so that third-party software does not need to add the
+              # -F/#{HOMEBREW_PREFIX}/Frameworks switch.
+              # Assume Framework style build (default since months in brew)
+              try:
+                  from _sysconfigdata import build_time_vars
+                  build_time_vars['LINKFORSHARED'] = '-u _PyMac_Error #{HOMEBREW_PREFIX}/opt/#{name}/Frameworks/Python.framework/Versions/#{version.major}.#{version.minor}/Python'
+              except:
+                  pass  # remember: don't print here. Better to fail silent.
+          # Fix 5)
+          #   For all Pythons of the right major.minor version: Tell about homebrew's
+          #   site-packages location. This is needed for Python to parse *.pth.
+          import site
+          site.addsitedir('#{global_site_packages}')
+    EOF
+  end
+
+  def message
+    @unsatisfied_because
+  end
+
+  def <=> other
+    version <=> other.version
+  end
+
+  def to_s
+    binary.to_s
+  end
+
+  def hash
+    to_s.hash
+  end
+end
diff --git a/Library/Homebrew/superenv.rb b/Library/Homebrew/superenv.rb
index 18a47ca0d..022517534 100644
--- a/Library/Homebrew/superenv.rb
+++ b/Library/Homebrew/superenv.rb
@@ -30,7 +30,7 @@ class << ENV
   alias_method :x11?, :x11
 
   def reset
-    %w{CC CXX OBJC OBJCXX CPP MAKE LD
+    %w{CC CXX OBJC OBJCXX CPP MAKE LD LDSHARED
       CFLAGS CXXFLAGS OBJCFLAGS OBJCXXFLAGS LDFLAGS CPPFLAGS
       MACOS_DEPLOYMENT_TARGET SDKROOT
       CMAKE_PREFIX_PATH CMAKE_INCLUDE_PATH CMAKE_FRAMEWORK_PATH
@@ -57,7 +57,7 @@ class << ENV
     ENV['HOMEBREW_BREW_FILE'] = HOMEBREW_BREW_FILE
     ENV['HOMEBREW_SDKROOT'] = "#{MacOS.sdk_path}" if MacSystem.xcode43_without_clt?
     ENV['CMAKE_PREFIX_PATH'] = determine_cmake_prefix_path
-    ENV['CMAKE_FRAMEWORK_PATH'] = "#{MacOS.sdk_path}/System/Library/Frameworks" if MacSystem.xcode43_without_clt?
+    ENV['CMAKE_FRAMEWORK_PATH'] = determine_cmake_frameworks_path
     ENV['CMAKE_INCLUDE_PATH'] = determine_cmake_include_path
     ENV['CMAKE_LIBRARY_PATH'] = determine_cmake_library_path
     ENV['ACLOCAL_PATH'] = determine_aclocal_path
@@ -133,7 +133,6 @@ class << ENV
       paths << "#{MacOS::Xcode.prefix}/Toolchains/XcodeDefault.xctoolchain/usr/bin"
     end
     paths += deps.map{|dep| "#{HOMEBREW_PREFIX}/opt/#{dep}/bin" }
-    paths << "#{HOMEBREW_PREFIX}/opt/python/bin" if brewed_python?
     paths << "#{MacSystem.x11_prefix}/bin" if x11?
     paths += %w{/usr/bin /bin /usr/sbin /sbin}
     paths.to_path_s
@@ -158,6 +157,14 @@ class << ENV
     paths.to_path_s
   end
 
+  def determine_cmake_frameworks_path
+    # XXX: keg_only_deps perhaps? but Qt does not link its Frameworks because of Ruby's Find.find ignoring symlinks!!
+    paths = deps.map{|dep| "#{HOMEBREW_PREFIX}/opt/#{dep}/Frameworks" }
+    paths << "#{HOMEBREW_PREFIX}/Frameworks"
+    paths << "#{MacOS.sdk_path}/System/Library/Frameworks" if MacSystem.xcode43_without_clt?
+    paths.to_path_s
+  end
+
   def determine_cmake_include_path
     sdk = MacOS.sdk_path if MacSystem.xcode43_without_clt?
     paths = []
@@ -165,11 +172,6 @@ class << ENV
     paths << "#{sdk}/usr/include/libxml2" unless deps.include? 'libxml2'
     if MacSystem.xcode43_without_clt?
       paths << "#{sdk}/usr/include/apache2"
-      paths << if brewed_python?
-        "#{HOMEBREW_PREFIX}/opt/python/Frameworks/Python.framework/Headers"
-      else
-        "#{sdk}/System/Library/Frameworks/Python.framework/Versions/Current/include/python2.7"
-      end
     end
     paths << "#{sdk}/System/Library/Frameworks/OpenGL.framework/Versions/Current/Headers/" unless x11?
     paths << "#{MacSystem.x11_prefix}/include" if x11?
@@ -227,11 +229,6 @@ class << ENV
     MacOS::Xcode.prefix || ENV['DEVELOPER_DIR']
   end
 
-  def brewed_python?
-    require 'formula'
-    Formula.factory('python').linked_keg.directory?
-  end
-
   public
 
 ### NO LONGER NECESSARY OR NO LONGER SUPPORTED
diff --git a/Library/Homebrew/test/test_build_options.rb b/Library/Homebrew/test/test_build_options.rb
index daf5ef96b..cc5fd01d7 100644
--- a/Library/Homebrew/test/test_build_options.rb
+++ b/Library/Homebrew/test/test_build_options.rb
@@ -42,4 +42,15 @@ class BuildOptionsTests < Test::Unit::TestCase
   def test_unused_options
     assert @build.unused_options.include?("--without-baz")
   end
+
+  def test_implicit_options
+    # --without-baz is not explicitly specified on the command line
+    # therefore --with-baz should be implicitly assumed:
+    assert @build.implicit_options.include?("--with-baz")
+    # But all these should not be in the implict_options:
+    assert !@build.implicit_options.include?("--without-baz")
+    assert !@build.implicit_options.include?("--with-bar")
+    assert !@build.implicit_options.include?("--without-bar")
+    assert !@build.implicit_options.include?("--with-qux")
+  end
 end
diff --git a/Library/Homebrew/test/test_python.rb b/Library/Homebrew/test/test_python.rb
new file mode 100644
index 000000000..7658efa85
--- /dev/null
+++ b/Library/Homebrew/test/test_python.rb
@@ -0,0 +1 @@
+#TODO!
\ No newline at end of file
diff --git a/Library/Homebrew/utils.rb b/Library/Homebrew/utils.rb
index e959d9d64..60eead67c 100644
--- a/Library/Homebrew/utils.rb
+++ b/Library/Homebrew/utils.rb
@@ -97,7 +97,7 @@ module Homebrew
     fork do
       yield if block_given?
       args.collect!{|arg| arg.to_s}
-      exec(cmd, *args) rescue nil
+      exec(cmd.to_s, *args) rescue nil
       exit! 1 # never gets here unless exec failed
     end
     Process.wait