vim – 如何设置Syntastic作为python3检查器而不是python2

print "Hello world! python2"

,这显然是python3的错误,但是
运行后：w保存文件,没有错误信息,
以下是?/ .vimrc的一部分,它是关于Syntastic的：

" Syntastic                                                                     
"" Recommended settings                                                         
set statusline+=%#warningmsg#                                                   
set statusline+=%{SyntasticStatuslineFlag()}                                    
set statusline+=%*                                                              
let g:syntastic_always_populate_loc_list = 1                                    
let g:syntastic_auto_loc_list = 1                                               
let g:syntastic_check_on_open = 1                                               

"" Display checker-name for that error-message                                  
let g:syntastic_aggregate_errors = 1        

"" I use the brew to install flake8                                             
let g:syntastic_python_checkers=['flake8','python3']

如何在终端中运行test.py时使Syntastic检测到这种类型的错误：

NingGW:Desktop ninggw$python3 test.py
  File "test.py",line 1
    print "Hello world! python2"
                               ^
SyntaxError: Missing parentheses in call to 'print'

以下是：SyntasticInfo说：

Syntastic version: 3.8.0-10 (Vim 800,Darwin,GUI)
Info for filetype: python
Global mode: active
Filetype python is active
The current file will be checked automatically
Available checkers: flake8 python
Currently enabled checker: flake8
Press ENTER or type command to continue