PythonInstalled: Don't require superenv

* The python do ... end block does no longer
  require 'superenv' but saves and restores
  the ENV by using ENV.to_hash and `ensure`.
  This should resolve some build problems
  with formulae using `env :std`!
* `python_helper` is now in a module `Python`.
* Imporoved some comments in python_dependency.rb

Library/Homebrew/formula.rb

@@ -307,7 +307,7 @@ class Formula
 
   def python(options={:allowed_major_versions => [2, 3]}, &block)
     require 'python_helper'
-    python_helper(options, &block)
+    Python::python_helper(options, &block)
   end
 
   # Explicitly only execute the block for 2.x (if a python 2.x is available)

Library/Homebrew/python_helper.rb

@@ -2,16 +2,17 @@
 # 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)
+module Python
+  # 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.
@@ -51,9 +52,9 @@ def python_helper(options={:allowed_major_versions => [2, 3]}, &block)
           return py
         else
           puts "brew: Python block (#{py.binary})..." if ARGV.verbose? && ARGV.debug?
-        require 'superenv'
-        # Ensure env changes are only temporary by using `with_build_environment`
-        ENV.with_build_environment do
+          # Ensure env changes are only temporary
+          begin
+            old_env = ENV.to_hash
             # 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
@@ -72,8 +73,12 @@ def python_helper(options={:allowed_major_versions => [2, 3]}, &block)
             res = instance_eval(&block)
             @current_python = nil
             res
+          ensure
+            ENV.replace(old_env)
           end
         end
       end
     end
+  end  # enf of python_helper method
+
 end

Library/Homebrew/requirements/python_dependency.rb

@@ -128,8 +128,8 @@ class PythonInstalled < Requirement
     "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.
+  # Homebrew's global site-packages. The local ones (just `site_packages`) 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
@@ -230,7 +230,7 @@ class PythonInstalled < Requirement
     ENV.append 'CMAKE_INCLUDE_PATH', incdir, ':'
     ENV.append 'PKG_CONFIG_PATH', pkg_config_path, ':' if pkg_config_path
     # We don't set the -F#{framework} here, because if Python 2.x and 3.x are
-    # used, `Python.framework` is ambuig. However, in the `python do` block
+    # used, `Python.framework` is ambiguous. However, in the `python do` block
     # we can set LDFLAGS+="-F#{framework}" because only one is temporarily set.
 
     # Udpate distutils.cfg (later we can remove this, but people still have