How to use Multi-input in OpenNmt-py?

In openNMT-tf i found the Multi-input source, but why it does not realized in OpenNmt-py?

This is not supported yet.

However, if the second source has always the same length as the first one (e.g. word annotations), you could use word features. See the documentation for OpenNMT-lua (OpenNMT-py uses the same syntax):