venv 是 Python3.3 以后的功能，官方文档在此。
After I learned how to write makefile, I found that this was not enough to enable me to build all projects, such as KDE, OpenCV and so on. So I determined to learn CMake, an awesome building tool, which can be use on all platforms. You can download CMake by this page.
What is makefile? Most Windows developers don’t know this, and it is useful in Linux development. Most often, the makefile directs Make on how to compile and link a program.