old_contents: # -*- coding: utf-8 -*-
  # Licensed under a 3-clause BSD style license - see LICENSE.rst
  
  from __future__ import (absolute_import, division, print_function,
                          unicode_literals)
  
  import os
  import sys
  
  if sys.version_info >= (3, 3):
      # OS X framework builds of Python 3.3 can not call other 3.3
      # virtualenvs as a subprocess because `__PYENV_LAUNCHER__` is
      # inherited.
      if os.environ.get('__PYVENV_LAUNCHER__'):
          os.unsetenv('__PYVENV_LAUNCHER__')
  
new_contents: # -*- coding: utf-8 -*-
  # Licensed under a 3-clause BSD style license - see LICENSE.rst
  
  from __future__ import (absolute_import, division, print_function,
                          unicode_literals)
  
  import os
  import sys
  
  if sys.version_info >= (3, 3):
      # OS X framework builds of Python 3.3 can not call other 3.3
      # virtualenvs as a subprocess because `__PYENV_LAUNCHER__` is
      # inherited.
      if os.environ.get('__PYVENV_LAUNCHER__'):
          os.unsetenv('__PYVENV_LAUNCHER__')
  
  
  def check_version_compatibility():
      """
      Performs a number of compatibility checks with third-party
      libraries.
      """
      from distutils.version import LooseVersion
  
      if sys.version_info[0] == 3:
          import virtualenv
          if LooseVersion(virtualenv.__version__) == LooseVersion('1.11'):
              raise RuntimeError("asv is not compatible with Python 3.x and virtualenv 1.11")
  
  
  check_version_compatibility()
  
subject: Add version check for incompatible Python 3.x/virtualenv 1.11 combination