This blog post is an announcement for pysshsftp, a proof-of-concept, educational SFTP client for Unix, which uses the OpenSSH ssh(1) command-line tool (for establishing the secure connection), but it doesn't use the sftp(1) command-line tool (so it can e.g. upload files without truncating them first).
Only very little part of the SFTP protocol has been implemented so far (initialization, uploading, and stat()ting files). The SFTP protocol was reverse-engineered from sftp-client.c in the OpenSSH 5.1 source code.
The motivation behind writing pysshsftp was to have an SFTP client which
- supports uploading files without truncating them (the OpenSSH sftp(1) always truncates the file before uplading data bytes);
- can be easily scripted from Python;
- uses the OpenSSH(1) command-line tool for establishing the secure connection (other Python libraries like pysftp and paramiko can't use the user's public key configuration properly by default: they don't support passphrase reading for passphrase-protected keys, they don't support reading keys from ssh-agent, and they don't support reading
~/.ssh/id_dsaexactly the same way as OpenSSH uses them).