Pysftp-Shell
This is a thin wrapper over pysftp to provide a more useful shell than the standard sftp shell. Improvements include autocomplete based on the files in the current directoy, in-memory history navigation, and arrow key usage.
Honestly it's just prompt_toolkit on the front end and pysftp on the backend with some error handling in the middle.
Start it with ftp_prompt.py $hostname $username. It'll ask you for a password, then you're good to go.