zsh:未找到命令：flake8，但已安装flake8

Question

我试图在我的python代码上运行flake8 linter，但是我遇到了一些问题。

运行pip install会给出以下响应：

~ pip install flake8                                                                                                                                                                                                                                  
Requirement already satisfied: flake8 in ./Library/Python/2.7/lib/python/site-packages
Requirement already satisfied: enum34; python_version < "3.4" in ./Library/Python/2.7/lib/python/site-packages (from flake8)
Requirement already satisfied: configparser; python_version < "3.2" in ./Library/Python/2.7/lib/python/site-packages (from flake8)
Requirement already satisfied: mccabe<0.7.0,>=0.6.0 in ./Library/Python/2.7/lib/python/site-packages (from flake8)
Requirement already satisfied: pycodestyle<2.4.0,>=2.0.0 in ./Library/Python/2.7/lib/python/site-packages (from flake8)
Requirement already satisfied: pyflakes<1.6.0,>=1.5.0 in ./Library/Python/2.7/lib/python/site-packages (from flake8)

但当我试图运行它时，我得到了这个错误。

~ flake8 --version                                                                                                                                                                                                                                    
zsh: command not found: flake8

如果有什么不同的话，我也在用mac。

请大家帮忙。