When requesting a file-like object with open or file, or implicitly by using one of the upload or download methods, ftputil uses a "child session" behind the scenes, i. e. it implicitly makes a new connection to the FTP server. If a remote file has been opened and closed before, the associated FTP session is reused. At the moment, however, this is done without checking if the connection has already timed out.

I've never heard of actual problems regarding this behavior, but it isn't correct and could lead to mysterious surprises if it's triggered.

I'm planning to remedy this by doing a getcwd call on a child session before reusing it. If that turns out to be roughly as slow as building a new session in the first place, I'll consider to get rid of the session caching altogether, thereby simplifying the code a bit.