import paramiko
import contextlib

@contextlib.contextmanager
def open_sftp(hostname, port, username, password):
    # open ssh/sftp connection:
    client = paramiko.SSHClient()
    client.load_system_host_keys()
    client.set_missing_host_key_policy(paramiko.AutoAddPolicy())
    try:
        client.connect(hostname=hostname, port=port, username=username, password=password)
        sftp = client.open_sftp()
        yield sftp

    finally:
        sftp.close()
        client.close()