请问 pylint 是什么？为何我的 VScode 总是因它报错？

在每次保存py文件时提示：
Linter pylint is not installed
然后我点击右侧的 Install pylint
在终端上出现

C:\Users\Python>python -m pip install pylint
Requirement already satisfied: pylint in c:\python27\lib\site-packages
Requirement already satisfied: astroid<1.5.0,>=1.4.5 in c:\python27\lib\site-packages (from pylint)
Requirement already satisfied: mccabe in c:\python27\lib\site-packages (from pylint)
Requirement already satisfied: configparser; python_version == "2.7" in c:\python27\lib\site-packages (from pylint)
Requirement already satisfied: backports.functools-lru-cache; python_version == "2.7" in c:\python27\lib\site-packages (from pylint)
Requirement already satisfied: six in c:\python27\lib\site-packages (from pylint)
Requirement already satisfied: colorama; sys_platform == "win32" in c:\python27\lib\site-packages (from pylint)
Requirement already satisfied: isort>=4.2.5 in c:\python27\lib\site-packages (from pylint)
Requirement already satisfied: wrapt in c:\python27\lib\site-packages (from astroid<1.5.0,>=1.4.5->pylint)
Requirement already satisfied: lazy-object-proxy in c:\python27\lib\site-packages (from astroid<1.5.0,>=1.4.5->pylint)