我如何修复virtualenv安装？

Question

我使用pip install virtualenv安装了virtualenv。这是我尝试检查安装时的终端输出

virtualenv --version
Traceback (most recent call last):
  File "/usr/local/bin/virtualenv", line 5, in <module>
    from pkg_resources import load_entry_point
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 2793, in <module>
    working_set.require(__requires__)
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 673, in require
    needed = self.resolve(parse_requirements(requirements))
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 576, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: virtualenv==1.11.6

我目前正在运行Python 2.7。