Python ImportError:在virtualenv中运行pip升级时无法导入名称HeaderParsingError

在python虚拟环境中，我无法通过pip安装任何东西

这是我运行的命令：

pip install --upgrade pip 

错误输出：

ImportError: cannot import name HeaderParsingError

整个回溯过程如下图所示：

(env)root@ali-Lenovo-G50-80:/home/ali# pip install --upgrade pip
Traceback (most recent call last):
  File "/home/ali/env/bin/pip", line 7, in <module>
    from pip import main
  File "/home/ali/env/local/lib/python2.7/site-packages/pip/__init__.py", line 11, in <module>
    from pip.vcs import git, mercurial, subversion, bazaar  # noqa
  File "/home/ali/env/local/lib/python2.7/site-packages/pip/vcs/mercurial.py", line 9, in <module>
    from pip.download import path_to_url
  File "/home/ali/env/local/lib/python2.7/site-packages/pip/download.py", line 22, in <module>
    from pip._vendor import requests, six
  File "/home/ali/env/local/lib/python2.7/site-packages/pip/_vendor/requests/__init__.py", line 58, in <module>
    from . import utils
  File "/home/ali/env/local/lib/python2.7/site-packages/pip/_vendor/requests/utils.py", line 25, in <module>
    from .compat import parse_http_list as _parse_list_header
  File "/home/ali/env/local/lib/python2.7/site-packages/pip/_vendor/requests/compat.py", line 7, in <module>
    from .packages import chardet
  File "/home/ali/env/local/lib/python2.7/site-packages/pip/_vendor/requests/packages/__init__.py", line 3, in <module>
    from . import urllib3
  File "/home/ali/env/local/lib/python2.7/site-packages/pip/_vendor/requests/packages/urllib3/__init__.py", line 16, in <module>
    from .connectionpool import (
  File "/home/ali/env/local/lib/python2.7/site-packages/pip/_vendor/requests/packages/urllib3/connectionpool.py", line 33, in <module>
    from .connection import (
  File "/home/ali/env/local/lib/python2.7/site-packages/pip/_vendor/requests/packages/urllib3/connection.py", line 41, in <module>
    from .util import (
  File "/home/ali/env/local/lib/python2.7/site-packages/pip/_vendor/requests/packages/urllib3/util/__init__.py", line 5, in <module>
    from .response import is_fp_closed
  File "/home/ali/env/local/lib/python2.7/site-packages/pip/_vendor/requests/packages/urllib3/util/response.py", line 4, in <module>
    from ..exceptions import HeaderParsingError
ImportError: cannot import name HeaderParsingError

（env）root@ali-Lenovo-G50-80:/home/ali#pip安装--升级pip
回溯（最近一次呼叫最后一次）：
文件“/home/ali/env/bin/pip”，第7行，在
从pip导入主
文件“/home/ali/env/local/lib/python2.7/site-packages/pip/_-init__.py”，第11行，在
从pip.vcs导入git、mercurial、subversion、bazaar#noqa
文件“/home/ali/env/local/lib/python2.7/site packages/pip/vcs/mercurial.py”，第9行，在
从pip.download导入路径\u到\u url
文件“/home/ali/env/local/lib/python2.7/site packages/pip/download.py”，第22行，在
来自pip.\u供应商进口请求，六个
文件“/home/ali/env/local/lib/python2.7/site packages/pip/_vendor/requests/_init__.py”，第58行，在
从…起导入UTIL
文件“/home/ali/env/local/lib/python2.7/site packages/pip/_vendor/requests/utils.py”，第25行，在
from.compat导入解析http列表作为解析列表头
文件“/home/ali/env/local/lib/python2.7/site packages/pip/_vendor/requests/compat.py”，第7行，在
from.packagesimport chardet
文件“/home/ali/env/local/lib/python2.7/site-packages/pip/_-vendor/requests/packages/_-init___.py”，第3行，在
从…起导入urllib3
文件“/home/ali/env/local/lib/python2.7/site-packages/pip/_-vendor/requests/packages/urllib3/__-init___.py”，第16行
from.connectionpool导入(
文件“/home/ali/env/local/lib/python2.7/site packages/pip/_vendor/requests/packages/urllib3/connectionpool.py”，第33行，在
从。连接导入(
文件“/home/ali/env/local/lib/python2.7/site packages/pip/_vendor/requests/packages/urllib3/connection.py”，第41行，在
从.util导入(
文件“/home/ali/env/local/lib/python2.7/site-packages/pip/_-vendor/requests/packages/urllib3/util/___;u-init.py”，第5行
from.response导入已关闭
文件“/home/ali/env/local/lib/python2.7/site packages/pip/_vendor/requests/packages/urllib3/util/response.py”，第4行，在
从..异常导入HeaderParsingError
ImportError:无法导入名称HeaderParsingError

有什么帮助吗？

可能的副本