创建虚拟环境没有成功：

python3 -m venv venv

错误提示：

The virtual environment was not created successfully because ensurepip is not
available.  On Debian/Ubuntu systems, you need to install the python3-venv
package using the following command.

    apt-get install python3-venv

You may need to use sudo with that command.  After installing the python3-venv
package, recreate your virtual environment.

查看本地python版本为3.4

解决办法：

sudo apt-get install python3.4-venv

Then use this:

python3 -m venv venv