pip install fails with “connection error: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:598)”

-----> pip install gensim config --global http.sslVerify false 可以把配置关闭

Just install any package with the "config --global http.sslVerify false" statement

You can ignore SSL errors by setting pypi.org and files.pythonhosted.org as trusted hosts. 或者安装的时候，信任站点

$ pip install --trusted-host pypi.org --trusted-host files.pythonhosted.org <package_name>

Note: Sometime during April 2018, the Python Package Index was migrated from pypi.python.org to pypi.org. This means "trusted-host" commands using the old domain no longer work.

Permanent Fix

Since the release of pip 10.0, you should be able to fix this permanently just by upgrading pip itself:

$ pip install --trusted-host pypi.org --trusted-host files.pythonhosted.org pip setuptools

Or by just reinstalling it to get the latest version:

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

(… and then running get-pip.py with the relevant Python interpreter).

pip install <otherpackage> should just work after this. If not, then you will need to do more, as explained below.

You may want to add the trusted hosts and proxy to your config file.

pip.ini (Windows) or pip.conf (unix)

[global]
trusted-host = pypi.python.org
               pypi.org
               files.pythonhosted.org

Alternate Solutions (Less secure)

Most of the answers could pose a security issue.

Two of the workarounds that help in installing most of the python packages with ease would be:

Using easy_install: if you are really lazy and don't want to waste much time, use easy_install <package_name>. Note that some packages won't be found or will give small errors.
Using Wheel: download the Wheel of the python package and use the pip command pip install wheel_package_name.whl to install the package.