我尝试过：
$sudo pip install virtualenv
$pip install virtualenv
$sudo pip3 install -U virtualenv
但是我遇到了这个异常：
Exception:
Traceback (most recent call last):
File "/usr/lib/python2.7/dist- packages/pip/basecommand. py', line 215, in main
status = self.run(options, args)
File '/usr/lib/python2.7/dist-packages/pip/wheel. py", line 749, in build
self.requirement_set.prepare_files(self.finder)