由于某些原因，我在用pip安装新软件包时遇到问题。我有一个OS Sierra环境，以前一切正常。现在，无论我是否使用virtualenv，我都会得到：

Collecting requests
Could not find a version that satisfies the requirement requests (from 
  versions: )
No matching distribution found for requests

这不仅适用于“请求”库，还适用于所有其他库（例如django等）。

我有最新的点子：

 pip --version
 returns: pip 9.0.1 from /Library/Python/2.7/site-packages/pip-9.0.1-py2.7.egg (python 2.7)

而我的python版本是：2.7.12

此外，根据本文，我检查了是否可以卷曲PyPi网站，并且确实得到了回复。

知道有什么问题吗？

已编辑

我以如下方式执行pip安装：

pip install -vvv requests

我得到了错误的详细输出：

Collecting requests
  2 location(s) to search for versions of requests:
  * http://pypi.python.org/simple/requests/
  * http://pypi.wfp.org/simple/requests/
  Getting page http://pypi.python.org/simple/requests/
  Starting new HTTP connection (1): pypi.python.org
  "GET /simple/requests/ HTTP/1.1" 403 16
  Could not fetch URL http://pypi.python.org/simple/requests/: 403 Client 
  Error: SSL is required for url: http://pypi.python.org/simple/requests/ - 
  skipping
  Getting page http://pypi.wfp.org/simple/requests/
  Starting new HTTP connection (1): pypi.wfp.org
  "GET /simple/requests/ HTTP/1.1" 404 None
  Could not fetch URL http://pypi.wfp.org/simple/requests/: 404 Client 
  Error: NOT FOUND for url: http://pypi.wfp.org/simple/requests/ - skipping
  Could not find a version that satisfies the requirement requests (from 
  versions: )
 Cleaning up...
  No matching distribution found for requests
 Exception information:
 Traceback (most recent call last):
 File "/Library/Python/2.7/site-packages/pip-9.0.1-
py2.7.egg/pip/basecommand.py", line 215, in main
  status = self.run(options, args)
 File "/Library/Python/2.7/site-packages/pip-9.0.1-
py2.7.egg/pip/commands/install.py", line 324, in run
requirement_set.prepare_files(finder)
File "/Library/Python/2.7/site-packages/pip-9.0.1-
py2.7.egg/pip/req/req_set.py", line 380, in prepare_files
ignore_dependencies=self.ignore_dependencies))
File "/Library/Python/2.7/site-packages/pip-9.0.1-
py2.7.egg/pip/req/req_set.py", line 554, in _prepare_file
require_hashes
File "/Library/Python/2.7/site-packages/pip-9.0.1-
py2.7.egg/pip/req/req_install.py", line 278, in populate_link
self.link = finder.find_requirement(self, upgrade)
File "/Library/Python/2.7/site-packages/pip-9.0.1-py2.7.egg/pip/index.py", 
line 514, in find_requirement
'No matching distribution found for %s' % req
DistributionNotFound: No matching distribution found for requests