尝试创建虚拟环境时出错

Question

我想学习django，所以我尝试创建一个虚拟环境，我收到此错误：

mkvirtualenv django

Traceback (most recent call last):
  File "/usr/local/bin/virtualenv", line 5, in <module>
    from pkg_resources import load_entry_point
  File "/Library/Python/2.7/site-packages/distribute-0.6.49-py2.7.egg/pkg_resources.py", line 2881, in <module>
    parse_requirements(__requires__), Environment()
  File "/Library/Python/2.7/site-packages/distribute-0.6.49-py2.7.egg/pkg_resources.py", line 596, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: virtualenv==1.8.2

我有一段时间没用过python所以我不确定问题是什么：

 virtualenv --version
Traceback (most recent call last):
  File "/usr/local/bin/virtualenv", line 5, in <module>
    from pkg_resources import load_entry_point
  File "/Library/Python/2.7/site-packages/distribute-0.6.49-py2.7.egg/pkg_resources.py", line 2881, in <module>
    parse_requirements(__requires__), Environment()
  File "/Library/Python/2.7/site-packages/distribute-0.6.49-py2.7.egg/pkg_resources.py", line 596, in resolve
    raise DistributionNotFound(req)
pkg_resources.DistributionNotFound: virtualenv==1.8.2