Set pythonhome and pythonthreehome automatically

MacVim uses Homebrew python2 if installed, otherwise System's
MacVim uses Homebrew python3 if installed, next try to use python.org binary

Author: splhack

runtime/doc/options.txt

@@ -5929,6 +5929,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 			{not in Vi}
 			{only available when compiled with the |+python/dyn|
 			feature}
+	Note: EXPERIMENTAL. It may be changed or removed in the future.
 	Specifies the name of the Python 2.x home directory. When 'pythonhome'
 	and the PYTHONHOME environment variable are not set, PYTHON_HOME,
 	which was specified at compile time, will be used for the Python 2.x
@@ -5955,6 +5956,7 @@ A jump table for the options with a short description can be found at |Q_op|.
 			{not in Vi}
 			{only available when compiled with the |+python3/dyn|
 			feature}
+	Note: EXPERIMENTAL. It may be changed or removed in the future.
 	Specifies the name of the Python 3 home directory. When
 	'pythonthreehome' and the PYTHONHOME environment variable are not set,
 	PYTHON3_HOME, which was specified at compile time, will be used for

src/MacVim/vimrc

@@ -13,3 +13,25 @@ set backspace+=indent,eol,start
 " the entire MacVim menu is set up in a nib file which currently only is
 " translated to English).
 set langmenu=none
+
+" Python2
+" MacVim uses Homebrew python2 if installed, otherwise configured one
+if exists("&pythondll") && exists("&pythonhome")
+  if filereadable("/usr/local/Frameworks/Python.framework/Versions/2.7/Python")
+    " Homebrew python 2.7
+    set pythondll=/usr/local/Frameworks/Python.framework/Versions/2.7/Python
+    set pythonhome=/usr/local/Frameworks/Python.framework/Versions/2.7
+  endif
+endif
+
+" Python3
+" MacVim uses Homebrew python3 if installed, next try to use python.org binary
+if exists("&pythonthreedll") && exists("&pythonthreehome") &&
+      \ !filereadable(&pythonthreedll)
+  if filereadable("/Library/Frameworks/Python.framework/Versions/3.5/Python")
+    " https://www.python.org/downloads/mac-osx/
+    set pythonthreedll=/Library/Frameworks/Python.framework/Versions/3.5/Python
+    set pythonthreehome=/Library/Frameworks/Python.framework/Versions/3.5
+  endif
+endif
+