我正在尝试在Ubuntu 12.04上使用devstack安装openstack。这是我得到的错误：
+ set +o xtrace
+ sudo PIP_DOWNLOAD_CACHE=/var/cache/pip HTTP_PROXY= HTTPS_PROXY= NO_PROXY= /usr/local/bin/pip install --build=/tmp/pip-build.9BPNh 'prettytable>0.7'
Downloading/unpacking prettytable>0.7
Cannot fetch index base URL https://pypi.python.org/simple/
Could not find any downloads that satisfy the requirement prettytable>0.7
Cleaning up...
No distributions at all found for prettytable>0.7
Storing complete log in /home/vagrant/.pip/pip.log
这是日志：
vagrant@precise32:~/devstack$ cat /home/vagrant/.pip/pip.log
------------------------------------------------------------
/usr/local/bin/pip run on Fri Apr 11 12:02:37 2014
Downloading/unpacking prettytable>0.7
Getting page https://pypi.python.org/simple/prettytable/
Could not fetch URL https://pypi.python.org/simple/prettytable/: <urlopen error [Errno 111] Connection refused>
Will skip URL https://pypi.python.org/simple/prettytable/ when looking for download links for prettytable>0.7
Getting page https://pypi.python.org/simple/
Could not fetch URL https://pypi.python.org/simple/: <urlopen error [Errno 111] Connection refused>
Will skip URL https://pypi.python.org/simple/ when looking for download links for prettytable>0.7
Cannot fetch index base URL https://pypi.python.org/simple/
URLs to search for versions for prettytable>0.7:
* https://pypi.python.org/simple/prettytable/
Getting page https://pypi.python.org/simple/prettytable/
Could not fetch URL https://pypi.python.org/simple/prettytable/: <urlopen error [Errno 111] Connection refused>
Will skip URL https://pypi.python.org/simple/prettytable/ when looking for download links for prettytable>0.7
Could not find any downloads that satisfy the requirement prettytable>0.7
Cleaning up...
No distributions at all found for prettytable>0.7
Exception information:
Traceback (most recent call last):
File "/usr/local/lib/python2.7/dist-packages/pip-1.4.1-py2.7.egg/pip/basecommand.py", line 134, in main
status = self.run(options, args)
File "/usr/local/lib/python2.7/dist-packages/pip-1.4.1-py2.7.egg/pip/commands/install.py", line 236, in run
requirement_set.prepare_files(finder, force_root_egg_info=self.bundle, bundle=self.bundle)
File "/usr/local/lib/python2.7/dist-packages/pip-1.4.1-py2.7.egg/pip/req.py", line 1085, in prepare_files
url = finder.find_requirement(req_to_install, upgrade=self.upgrade)
File "/usr/local/lib/python2.7/dist-packages/pip-1.4.1-py2.7.egg/pip/index.py", line 265, in find_requirement
raise DistributionNotFound('No distributions at all found for %s' % req)
DistributionNotFound: No distributions at all found for prettytable>0.7
我不确定，为什么我会收到此错误，请你帮我解决一下。