python虚拟环境Virtualenvwrapper无法升降级虚拟环境软件解决方法

virtualenv用于创建独立的Python环境，多个Python相互独立，互不影响，它能够在没有权限的情况下安装新套件，不同应用可以使用不同的套件版本，套件升级不影响其他应用。

Virtaulenvwrapper则是virtualenv的扩展包，用于更方便管理虚拟环境，如，新增，删除，复制，切换等。

最近在利用Virtaulenvwrapper的mkvirtualenv创建Python虚拟环境的时候，发现在创建的虚拟环境中升级django为1.8的时候，出现无法升级的状况：（机器外部已经安装django-1.6.10）

shenweiyan@localhost :: ~
=> workon test
(test)shenweiyan@localhost :: ~
=> pip install --upgrade django==1.8
You are using pip version , however version  is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
Collecting django==1.8
  Using cached Django-1.8-py2.py3-none-any.whl
Installing collected packages: django
  Found existing installation: Django
    Not uninstalling Django at /usr/local/python2./lib/python2./site-packages, outside environment /App/pyweb/test

Successfully installed django-

提示无法在/usr/local/python2.7/lib/python2.7/site-packages安装django-1.8。其原因就在于在全局环境变量中已经指定了PYTHONPATH，所以在安装django的时候会把1.8的版本默认安装到指定的PYTHONPATH下，从而导致django-1.8无法成功安装。

root@localhost :: ~
=> cat /etc/profile
......
export PATH=/usr/local/python2./bin:$PATH
export PYTHONPATH=/usr/local/python2./lib/python2./site-packages:/usr/lib/python2./site-packages:$PYTHONPATH

所以，把/etc/profile全局变量中的PYTHONPATH注释掉，再重新登录虚拟环境进行安装升级就ok了。

shenweiyan@localhost :: ~
=> workon test
(test)shenweiyan@localhost :: ~
(test)shenweiyan@localhost :: ~
=> pip
You are using pip version , however version  is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
Collecting django==
  Using cached Django--py2.py3-none-any.whl
Installing collected packages: django
  Found existing installation: Django
    Uninstalling Django-:
      Successfully uninstalled Django-
Successfully installed django-

ok，问题解决！！！

---