python twainmodule 设置A3

[aec4d]

深夜求解答，使用python的twain模块扫描A3，如何设置成A3输入？
官网http://twainmodule.sourceforge.net/docs/caps.html也有坑，比如介绍的以下一段
To set the current value of the capability, use the SetCapability method. This method take three parameters, the identity of the capabaility (CAP_*, ICAP_* or ACAP_*), the type of the value (as returned from GetCapabilityCurrent), and the new value.

>>> ss.GetCapabilityCurrent(twain.ICAP_IMAGEFILEFORMAT, TWTY_UINT16, TWFF_JFIF)

正确写法应该是ss.SetCapability(twain.ICAP_IMAGEFILEFORMAT, twain.TWTY_UINT16, twain.TWFF_JFIF)

我使用twain twacker查询和设置ICAP_SUPPORTEDSIZE结果如下
http://bcs.duapp.com/picstore/aMqibomfDN.png
http://bcs.duapp.com/picstore/txfl7TNTeV.png

当然是用ss.SetCapability(twain.ICAP_IMAGEFILEFORMAT, twain.TWTY_UINT16, twain.TWSS_A3)
也是失败的，真感觉有点奇怪，为啥有这个值，但是设置的时候又会提示超出范围呢