python - ssh walk and search

class SSHSession(object):
    # Usage:
    # Detects DSA or RSA from key_file, either as a string filename or a
    # file object.  Password auth is possible, but I will judge you for
    # using it. So:
    # ssh=SSHSession('targetserver.com','root',key_file=open('mykey.pem','r'))
    # ssh=SSHSession('targetserver.com','root',key_file='/home/me/mykey.pem')
    # ssh=SSHSession('targetserver.com','root','mypassword')
    # ssh.put('filename','/remote/file/destination/path')
    # ssh.put_all('/path/to/local/source/dir','/path/to/remote/destination')
    # ssh.get_all('/path/to/remote/source/dir','/path/to/local/destination')
    # ssh.command('echo "Command to execute"')

    def __init__(self,hostname,username='root',key_file=None,password=None):
        #
        #  Accepts a file-like object (anything with a readlines() function)
        #  in either dss_key or rsa_key with a private key.  Since I don't
        #  ever intend to leave a server open to a password auth.
        #
        self.sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
        self.sock.connect((hostname,22))
        self.t = paramiko.Transport(self.sock)
        self.t.start_client()
        keys = paramiko.util.load_host_keys(os.path.expanduser('~/.ssh/known_hosts'))
        key = self.t.get_remote_server_key()
        # supposed to check for key in keys, but I don't much care right now to find the right notation
        if key_file is not None:
            if isinstance(key,str):
                key_file=open(key,'r')
            key_head=key_file.readline()
            key_file.seek(0)
            if 'DSA' in key_head:
                keytype=paramiko.DSSKey
            elif 'RSA' in key_head:
                keytype=paramiko.RSAKey
            else:
                raise Exception("Can't identify key type")
            pkey=keytype.from_private_key(key_file)
            self.t.auth_publickey(username, pkey)
        else:
            if password is not None:
                self.t.auth_password(username,password,fallback=False)
            else: raise Exception('Must supply either key_file or password')
        self.sftp=paramiko.SFTPClient.from_transport(self.t)


    def remote_walk(self, remotepath):
        dirs = []
        #files = []

        for f in self.sftp.listdir_attr(remotepath):
            if S_ISDIR(f.st_mode):
                if f.filename != '.' and f.filename != '..':
                    dirs.append(f.filename)
            #else:
            #    files.append(f.filename)

        #return dirs, files
        return dirs


    def find_folder(self, remotepath, foldername):
        print("find_folder:", remotepath, foldername)

        dirs = self.remote_walk(remotepath)

        if foldername in dirs:
           return os.path.join(remotepath, foldername)
        else:
            print("I am trying to find in child directories")
            for subfolder in dirs:
                subfolder_fullpath = os.path.join(remotepath, subfolder)
                print("subfolder:", subfolder)
                result = self.find_folder(subfolder_fullpath, foldername)
                # if found path then return it (in recursion)
                if results:
                    return result
                # else go back to `for` and check next subfolder

        #return None # it automatically returns None if can't find folder


###################################################
sshobject = SSHSession(hostname=host_name, username=test_user, key_file=None, password=test_password)
sshobject.find_folder(remotepath=str(base_dir), foldername="folder_name_to_search")