Ubuntu 16.04安装requests失败，提示module 'os'无PathLike属性

在Ubuntu 16.04系统中尝试安装requests模块，已尝试多种方案无效。系统已安装pip3，Python版本为2.7和3.5。执行命令pip3 install requests时出现以下报错：

Traceback (most recent call last):
File "/usr/lib/python3/dist-packages/pip/_vendor/__init__.py", line 33, in vendored
__import__(vendored_name, globals(), locals(), level=0)
ImportError: No module named 'pip._vendor.cachecontrol'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/home/pa/.local/lib/python3.5/site-packages/certifi/core.py", line 12, in 
<module>
from importlib.resources import path as get_path, read_text
ImportError: No module named 'importlib.resources'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/bin/pip3", line 9, in <module>
from pip import main
File "/usr/lib/python3/dist-packages/pip/__init__.py", line 13, in <module>
from pip.exceptions import InstallationError, CommandError, PipError
File "/usr/lib/python3/dist-packages/pip/exceptions.py", line 6, in <module>
from pip._vendor.six import iteritems
File "/usr/lib/python3/dist-packages/pip/_vendor/__init__.py", line 64, in <module>
vendored("cachecontrol")
File "/usr/lib/python3/dist-packages/pip/_vendor/__init__.py", line 36, in vendored
__import__(modulename, globals(), locals(), level=0)
File "<frozen importlib._bootstrap>", line 969, in _find_and_load
File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 664, in _load_unlocked
File "<frozen importlib._bootstrap>", line 634, in _load_backward_compatible
File "/usr/share/python-wheels/CacheControl-0.11.5-py2.py3-none-any.whl/cachecontrol/__init__.py", line 9, in <module>
File "<frozen importlib._bootstrap>", line 969, in _find_and_load
File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 664, in _load_unlocked
File "<frozen importlib._bootstrap>", line 634, in _load_backward_compatible
File "/usr/share/python-wheels/CacheControl-0.11.5-py2.py3-none-any.whl/cachecontrol/wrapper.py", line 1, in <module>
File "<frozen importlib._bootstrap>", line 969, in _find_and_load
File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 664, in _load_unlocked
File "<frozen importlib._bootstrap>", line 634, in _load_backward_compatible
File "/usr/share/python-wheels/CacheControl-0.11.5-py2.py3-none-any.whl/cachecontrol/adapter.py", line 3, in <module>
File "<frozen importlib._bootstrap>", line 969, in _find_and_load
File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 664, in _load_unlocked
File "<frozen importlib._bootstrap>", line 634, in _load_backward_compatible
File "/usr/share/python-wheels/requests-2.9.1-py2.py3-none-any.whl/requests/__init__.py", line 58, in <module>
File "<frozen importlib._bootstrap>", line 969, in _find_and_load
File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 664, in _load_unlocked
File "<frozen importlib._bootstrap>", line 634, in _load_backward_compatible
File "/usr/share/python-wheels/requests-2.9.1-py2.py3-none-any.whl/requests/utils.py", line 25, in <module>
File "<frozen importlib._bootstrap>", line 969, in _find_and_load
File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
File "<frozen importlib._bootstrap>", line 664, in _load_unlocked
File "<frozen importlib._bootstrap>", line 634, in _load_backward_compatible
File "/usr/share/python-wheels/requests-2.9.1-py2.py3-none-any.whl/requests/certs.py", line 17, in <module>
File "/home/pa/.local/lib/python3.5/site-packages/certifi/__init__.py", line 1, in 
<module>
from .core import contents, where
File "/home/pa/.local/lib/python3.5/site-packages/certifi/core.py", line 44, in 
<module>
Resource = Union[str, "os.PathLike"]
File "/usr/lib/python3.5/typing.py", line 552, in __getitem__
dict(self.__dict__), parameters, _root=True)
File "/usr/lib/python3.5/typing.py", line 512, in __new__
for t2 in all_params - {t1} if not isinstance(t2, TypeVar)):
File "/usr/lib/python3.5/typing.py", line 512, in <genexpr>
for t2 in all_params - {t1} if not isinstance(t2, TypeVar)):
File "/usr/lib/python3.5/typing.py", line 190, in __subclasscheck__
self._eval_type(globalns, localns)
File "/usr/lib/python3.5/typing.py", line 177, in _eval_type
eval(self.__forward_code__, globalns, localns),
File "<string>", line 1, in <module>
AttributeError: module 'os' has no attribute 'PathLike'

同时通过PyCharm安装也失败。

核心原因 #

Ubuntu 16.04自带的Python 3.5版本较老，os.PathLike是Python 3.6+才引入的特性，而当前安装的certifi版本过高，不兼容Python 3.5，导致pip调用时出错。

步骤 #

1. 卸载不兼容的certifi版本
   执行命令：

pip3 uninstall -y certifi

2. 安装兼容Python 3.5的certifi版本
   选择支持Python 3.5的最后一个certifi版本：

pip3 install certifi==2020.12.5

3. 安装兼容Python 3.5的requests版本
   requests从2.25.0开始不再支持Python 3.5，因此指定旧版本安装：

pip3 install requests==2.24.0

4. 若pip本身损坏，可重新安装pip3
   如果上述步骤执行时pip仍报错，先修复pip：

sudo apt-get install --reinstall python3-pip

再重复步骤1-3。

内容的提问来源于stack exchange，提问作者Jack