Python 如何通过pip忽略警告消息

当尝试使用pip安装时，我收到以下警告消息，如何拒绝此消息

Requirement already up-to-date: pyserial in c:\python27\lib\site-packages
←[31mDEPRECATION: The default format will switch to columns in the future. You can use --format=(legacy|columns) (or define a format=(legacy|columns) in your pip.conf under the [list] section) to disable this warning.←[0m

代码：-

try:
    import subprocess32
except ImportError:
    #pip.main(["install", "subprocess32"])
    try:
        cmd = "C:\Python2\python.exe -m pip install subprocess32"
        proc = subprocess.Popen(cmd.split(' '), stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        (output, error) = proc.communicate()
    except WindowsError, e:
        print "Please install subprocess32 using command \"C:\Python27\python.exe -m pip install subprocess32\""
        #sys.exit(1)