make sure we're dealing with strings

[kcr]

This seems to be necessary to make .interact() work under certain circumstances.

[kcr]

headdesk or maybe I was using it wrong.

[takluyver]

That doesn't look quite right. The log files should get bytes data if the spawn object doesn't have a specified encoding, and unicode data if it does (docs).

It looks like the interact machinery is sending bytes to the log files regardless of whether there's a specified encoding. You don't need to decode the data to pass it between stdin and the child terminal, but that introduces an inconsistency in the way the data is logged.