运行yolk-U最近我注意到pip需要从1.2.1升级到1.4.1，并尽职尽责地尝试用

pip install --upgrade pip

虽然再次运行yolk-U似乎确认升级成功（pip不再被列为过期），但这会生成一条错误消息

Downloading/unpacking pip from https://pypi.python.org/packages/source/p/pip/pip-1.4.1.tar.gz#md5=6afbb46aeb48abac658d4df742bff714
Downloading pip-1.4.1.tar.gz (445kB): 445kB downloaded
Running setup.py egg_info for package pip

  warning: no files found matching '*.html' under directory 'docs'
  warning: no previously-included files matching '*.rst' found under directory 'docs/_build'
  no previously-included directories found matching 'docs/_build/_sources'
Installing collected packages: pip
  Found existing installation: pip 1.2.1
  Uninstalling pip:
Exception:
Traceback (most recent call last):
  File "/Library/Python/2.7/site-packages/pip-1.2.1-py2.7.egg/pip/basecommand.py", line 107, in main
  File "/Library/Python/2.7/site-packages/pip-1.2.1-py2.7.egg/pip/commands/install.py", line 261, in run
  File "/Library/Python/2.7/site-packages/pip-1.2.1-py2.7.egg/pip/req.py", line 1162, in install
  File "/Library/Python/2.7/site-packages/pip-1.2.1-py2.7.egg/pip/req.py", line 495, in uninstall
  File "/Library/Python/2.7/site-packages/pip-1.2.1-py2.7.egg/pip/req.py", line 1492, in remove
  File "/Library/Python/2.7/site-packages/pip-1.2.1-py2.7.egg/pip/util.py", line 273, in renames
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/shutil.py", line 299, in move
os.unlink(src)
OSError: [Errno 13] Permission denied: '/usr/local/bin/pip'

在我随后使用pip的所有尝试中也这样做：

Traceback (most recent call last):
  File "/usr/local/bin/pip", line 5, in <module>
    from pkg_resources import load_entry_point
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 2603, in <module>
    line, p, specs = scan_list(VERSION,LINE_END,line,p,(1,2),"version spec")
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 666, in require
    continue    # try the next older version of project
  File "/System/Library/Frameworks/Python.framework/Versions/2.7/Extras/lib/python/pkg_resources.py", line 565, in resolve

pkg_resources.DistributionNotFound: pip==1.2.1

我看到类似的问题以前也被报道过，但是我看到的建议都没有帮助解决这个问题。

我卡住了，无法维护我的Python安装。

我使用OS10.8.4，Python2.7.2在/usr/bin/python.