First of all, sorry about the slow response.

Vinay: I don't quite understand why you use __PYVENV_LAUNCHER__: When I create a pyvenv using python 3.3 (with a oldish build from the 3.3 branch) sys.executable point to a binary in the venv without mucking with environment variables:

$ pyvenv-3.3 testenv
$ testenv/bin/python
Python 3.3.5+ (3.3:a36d469f31c1, Aug 13 2014, 09:04:41) 
[GCC 4.2.1 Compatible Apple LLVM 5.1 (clang-503.0.40)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.executable
'/Users/ronald/Projects/pyobjc-hg/pyobjc/x/testenv/bin/python'


If older version of Python 3.x don't do this that's a bug in those versions and it would be acceptable to use the environment variable with those versions to work around this bug.

I still not convinced that __PYVENV_LAUNCHER__ needs to be changed. It's highly likely that any use of __PYVENV_LAUNCHER__ outside of CPython itself is an indication of a bug in CPython that needs to be fixed there.