系统中同时存在python2和python3时 pip有时候更新后会报错 解决安装的方法如下

官网原链接：https://pip.pypa.io/en/stable/installing/

Installation

Do I need to install pip?

pip is already installed if you are using Python 2 >=2.7.9 or Python 3 >=3.4 downloaded from python.org or if you are working in a Virtual Environment created by virtualenv or pyvenv. Just make sure to upgrade pip.

Installing with get-pip.py

To install pip, securely download get-pip.py. [1]:

curl https://bootstrap.pypa.io/get-pip.py -o get-pip.py

Inspect get-pip.py for any malevolence. Then run the following:

　到这一步的时候，如果python2的pip坏了，就运行：python2 get-pip.py

　如果是python3的pip坏了，升级就运行：python3 get-pip.py

python get-pip.py

Warning

Be cautious if you are using a Python install that is managed by your operating system or another package manager. get-pip.py does not coordinate with those tools, and may leave your system in an inconsistent state.

get-pip.py also installs setuptools [2] and wheel if they are not already. setuptools is required to install source distributions. Both are required in order to build a Wheel Cache (which improves installation speed), although neither are required to install pre-built wheels.

Note

The get-pip.py script is supported on the same python version as pip. For the now unsupported Python 2.6, alternate script is available here.

get-pip.py options

--no-setuptools

If set, do not attempt to install setuptools

--no-wheel

If set, do not attempt to install wheel

get-pip.py allows pip install options and the general options. Below are some examples:

Install from local copies of pip and setuptools:

python get-pip.py --no-index --find-links=/local/copies

Install to the user site [3]:

python get-pip.py --user

Install behind a proxy:

python get-pip.py --proxy="http://[user:passwd@]proxy.server:port"

Using Linux Package Managers

See Installing pip/setuptools/wheel with Linux Package Managers in the Python Packaging User Guide.

Upgrading pip

On Linux or macOS:

pip install -U pip

On Windows [4]:

python -m pip install -U pip

Python and OS Compatibility

pip works with CPython versions 2.7, 3.3, 3.4, 3.5, 3.6 and also pypy.

This means pip works on the latest patch version of each of these minor versions. Previous patch versions are supported on a best effort approach.

pip works on Unix/Linux, macOS, and Windows.

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[1]	"Secure" in this context means using a modern browser or a tool like curl that verifies SSL certificates when downloading from https URLs.

[2]	Beginning with pip v1.5.1, get-pip.py stopped requiring setuptools to be installed first.

[3]	The pip developers are considering making --user the default for all installs, including get-pip.py installs of pip, but at this time, --user installs for pip itself, should not be considered to be fully tested or endorsed. For discussion, see Issue 1668.

[4]	https://github.com/pypa/pip/issues/1299