def getLogs(cls, appname, count, hostname=None, db=None):
        db = DBCache(db)
        if hostname is None:
            hostname = db.gethostname()

        with db as cursor:
            cursor.execute("""SELECT DISTINCT pid
                                FROM logging
                               WHERE application=?
                                 AND host=?
                               ORDER BY id DESC;""", (appname, hostname))
            try:
                instances = zip(*cursor.fetchall())[0]
            except IndexError:
                print "No logs found on system profile."
                sys.exit(1)

        if count == -1:
            count = len(instances)
        else:
            count = min(count, len(instances))
        for pid in instances[0:count]:
            yield list(cls._fromQuery("""WHERE application=?
                                           AND host=?
                                           AND pid=?
                                         ORDER BY id;""",
                                    (appname, hostname, pid)))

    def getAppNames(cls, hostname=None, db=None):
        app = namedtuple('Application', ['name', 'count'])

        db = DBCache(db)
        if hostname is None:
            hostname = db.gethostname()

        with db as cursor:
            cursor.execute("""SELECT application, count(1)
                                FROM (SELECT DISTINCT application, pid
                                        FROM logging
                                       WHERE host=?) AS `pids`
                               GROUP BY application;""", (hostname,))
            for row in cursor:
                yield app(*row)

    def __init__(self, backend=None, port=None, db=None):
        if backend and port:
            XMLConnection.__init__(self, backend, port)
            self.db = db
            return

        self.db = DBCache(db)
        self.log = MythLog('Python XML Connection')
        if backend is None:
            # use master backend
            backend = self.db.settings.NULL.MasterServerIP
        if re.match('(?:\d{1,3}\.){3}\d{1,3}',backend) or \
                    check_ipv6(backend):
            # process ip address
            host = self.db._gethostfromaddr(backend)
            self.host = backend
            self.port = int(self.db.settings[host].BackendStatusPort)
        else:
            # assume given a hostname
            self.host = backend
            self.port = int(self.db.settings[self.host].BackendStatusPort)
            if not self.port:
                # try a truncated hostname
                self.host = backend.split('.')[0]
                self.port = int(self.db.setting[self.host].BackendStatusPort)
                if not self.port:
                    raise MythDBError(MythError.DB_SETTING, 
                                        backend+': BackendStatusPort')

    def __init__(self, path=None, setting=None, db=None, useshell=True, prefix=''):
        DBCache.__init__(self, db=db)
        self.log = MythLog(self.logmodule, db=self)
        self.path = None

        if setting is not None:
            # pull local setting from database
            host = self.gethostname()
            self.path = self.settings[host][setting]
            if self.path is None:
                # see if that setting is applied globally
                self.path = self.settings['NULL'][setting]
            if self.path is None:
                # not set globally either, use supplied default
                self.path = path
            if self.path is None:
                # no default supplied, just error out
                raise MythDBError(MythError.DB_SETTING, setting, host)

        if self.path is None:
            # setting not given, use path from argument
            if path is None:
                raise MythError('Invalid input to System()')
            self.path = path

        if prefix:
            self.path = os.path.join(prefix, self.path)

        cmd = self.path.split()[0]
        if self.path.startswith('/'):
            # test full given path
            if not os.access(cmd, os.F_OK):
                raise MythFileError('Defined executable path does not exist.')
        else:
            # search command from PATH
            for folder in os.environ['PATH'].split(':'):
                if os.access(os.path.join(folder,cmd), os.F_OK):
                    self.path = os.path.join(folder,self.path)
                    break
            else:
                raise MythFileError('Defined executable path does not exist.')
                
        self.returncode = 0
        self.stderr = ''
        self.useshell = useshell

def findfile(filename, sgroup, db=None):
    """
    findfile(filename, sgroup, db=None) -> StorageGroup object

    Will search through all matching storage groups, searching for file.
    Returns matching storage group upon success.
    """
    db = DBCache(db)
    for sg in db.getStorageGroup(groupname=sgroup):
        # search given group
        if sg.local:
            if os.access(sg.dirname+filename, os.F_OK):
                return sg
    for sg in db.getStorageGroup():
        # not found, search all other groups
        if sg.local:
            if os.access(sg.dirname+filename, os.F_OK):
                return sg
    return None

class MythXML( XMLConnection ):
    """
    Provides convenient methods to access the backend XML server.
    """
    def __init__(self, backend=None, port=None, db=None):
        if backend and port:
            XMLConnection.__init__(self, backend, port)
            self.db = db
            return

        self.db = DBCache(db)
        self.log = MythLog('Python XML Connection')
        if backend is None:
            # use master backend
            backend = self.db.settings.NULL.MasterServerIP
        if re.match('(?:\d{1,3}\.){3}\d{1,3}',backend) or \
                    check_ipv6(backend):
            # process ip address
            host = self.db._gethostfromaddr(backend)
            self.host = backend
            self.port = int(self.db.settings[host].BackendStatusPort)
        else:
            # assume given a hostname
            self.host = backend
            self.port = int(self.db.settings[self.host].BackendStatusPort)
            if not self.port:
                # try a truncated hostname
                self.host = backend.split('.')[0]
                self.port = int(self.db.setting[self.host].BackendStatusPort)
                if not self.port:
                    raise MythDBError(MythError.DB_SETTING, 
                                        backend+': BackendStatusPort')

    def getServDesc(self):
        """
        Returns a dictionary of valid pages, as well as input and output
        arguments.
        """
        
        #TODO - handle namespaces better
        tree = self._queryTree('GetServDesc')
        index = tree.tag.rindex('}')+1
        find = lambda e,c: e.find('%s%s' % (tree.tag[:index], c))

        for a in find(tree, 'actionList'):
            act = [find(a,'name').text, {'in':[], 'out':[]}]
            for arg in find(a, 'argumentList'):
                argname = find(arg, 'name').text
                argdirec = find(arg, 'direction').text
                act[1][argdirec].append(argname)
            yield act

    def getHosts(self):
        """Returns a list of unique hostnames found in the settings table."""
        return self._request('Myth/GetHosts')\
                                        .readJSON()['StringList']['Values']

    def getKeys(self):
        """Returns a list of unique keys found in the settings table."""
        return self._request('Myth/GetKeys')\
                                        .readJSON()['StringList']['Values']

    def getSetting(self, key, hostname=None, default=None):
        """Retrieves a setting from the backend."""
        args = {'Key':key}
        if hostname:
            args['HostName'] = hostname
        if default:
            args['Default'] = default
        return self._request('Myth/GetSetting', **args)\
                         .readJSON()['SettingList']['Settings'][0]['Value']

    def getProgramGuide(self, starttime, endtime, startchan, numchan=None):
        """
        Returns a list of Guide objects corresponding to the given time period.
        """
        starttime = datetime.duck(starttime)
        endtime = datetime.duck(endtime)
        args = {'StartTime':starttime.isoformat().rsplit('.',1)[0],
                'EndTime':endtime.isoformat().rsplit('.',1)[0], 
                'StartChanId':startchan, 'Details':1}
        if numchan:
            args['NumOfChannels'] = numchan
        else:
            args['NumOfChannels'] = 1

        dat = self._request('Guide/GetProgramGuide', **args).readJSON()
        for chan in dat['ProgramGuide']['Channels']:
            for prog in chan['Programs']:
                prog['ChanId'] = chan['ChanId']
                yield Guide.fromJSON(prog, self.db)

    def getProgramDetails(self, chanid, starttime):
        """
        Returns a Program object for the matching show.
        """
        starttime = datetime.duck(starttime)
        args = {'ChanId': chanid, 'StartTime': starttime.isoformat()}
        return Program.fromJSON(
                self._request('Guide/GetProgramDetails', **args)\
#.........这里部分代码省略.........

    def __init__(self, backend=None, blockshutdown=False, events=False, db=None):
        self.db = DBCache(db)
        self.log = MythLog(self.logmodule, db=self.db)
        self.hostname = None

        self.sendcommands = True
        self.blockshutdown = blockshutdown
        self.receiveevents = events

        if backend is None:
            # no backend given, use master
            self.host = self.db.settings.NULL.MasterServerIP
            self.hostname = self.db._gethostfromaddr(self.host)

        else:
            backend = backend.strip('[]')
            query = "SELECT hostname FROM settings WHERE value=? AND data=?"
            if self._reip.match(backend):
                # given backend is IP address
                self.host = backend
                self.hostname = self.db._gethostfromaddr(
                                            backend, 'BackendServerIP')
            elif check_ipv6(backend):
                # given backend is IPv6 address
                self.host = backend
                self.hostname = self.db._gethostfromaddr(
                                            backend, 'BackendServerIP6')
            else:
                # given backend is hostname, pull address from database
                self.hostname = backend
                self.host = self.db._getpreferredaddr(backend)

        # lookup port from database
        self.port = int(self.db.settings[self.hostname].BackendServerPort)
        if not self.port:
            raise MythDBError(MythError.DB_SETTING, 'BackendServerPort',
                                            self.port)

        self._ident = '%s:%d' % (self.host, self.port)
        if self._ident in self._shared:
            # existing connection found
            self._conn = self._shared[self._ident]
            if self.sendcommands:
                if self._conn.command is None:
                    self._conn.command = self._newcmdconn()
                elif self.blockshutdown:
                    # upref block of shutdown
                    # issue command to backend if needed
                    self._conn.blockshutdown += 1
                    if self._conn.blockshutdown == 1:
                        self._conn.command.blockShutdown()
            if self.receiveevents:
                if self._conn.event is None:
                    self._conn.event = self._neweventconn()
        else:
            # no existing connection, create new
            self._conn = self._ConnHolder()

            if self.sendcommands:
                self._conn.command = self._newcmdconn()
                if self.blockshutdown:
                    self._conn.blockshutdown = 1
            if self.receiveevents:
                self._conn.event = self._neweventconn()

            self._shared[self._ident] = self._conn

        self._events = self._listhandlers()
        for func in self._events:
            self.registerevent(func)

class BECache( object ):
    """
    BECache(backend=None, noshutdown=False, db=None)
                                            -> MythBackend connection object

    Basic class for mythbackend socket connections.
    Offers connection caching to prevent multiple connections.

    'backend' allows a hostname or IP address to connect to. If not provided,
                connect will be made to the master backend. Port is always
                taken from the database.
    'db' allows an existing database object to be supplied.
    'noshutdown' specified whether the backend will be allowed to go into
                automatic shutdown while the connection is alive.

    Available methods:
        backendCommand()    - Sends a formatted command to the backend
                              and returns the response.
    """

    class _ConnHolder( object ):
        blockshutdown = 0
        command = None
        event = None

    logmodule = 'Python Backend Connection'
    _shared = weakref.WeakValueDictionary()
    _reip = re.compile('(?:\d{1,3}\.){3}\d{1,3}')

    def __repr__(self):
        return "<%s 'myth://%s:%d/' at %s>" % \
                (str(self.__class__).split("'")[1].split(".")[-1],
                 self.hostname, self.port, hex(id(self)))

    def __init__(self, backend=None, blockshutdown=False, events=False, db=None):
        self.db = DBCache(db)
        self.log = MythLog(self.logmodule, db=self.db)
        self.hostname = None

        self.sendcommands = True
        self.blockshutdown = blockshutdown
        self.receiveevents = events

        if backend is None:
            # no backend given, use master
            self.host = self.db.settings.NULL.MasterServerIP
            self.hostname = self.db._gethostfromaddr(self.host)

        else:
            backend = backend.strip('[]')
            query = "SELECT hostname FROM settings WHERE value=? AND data=?"
            if self._reip.match(backend):
                # given backend is IP address
                self.host = backend
                self.hostname = self.db._gethostfromaddr(
                                            backend, 'BackendServerIP')
            elif check_ipv6(backend):
                # given backend is IPv6 address
                self.host = backend
                self.hostname = self.db._gethostfromaddr(
                                            backend, 'BackendServerIP6')
            else:
                # given backend is hostname, pull address from database
                self.hostname = backend
                self.host = self.db._getpreferredaddr(backend)

        # lookup port from database
        self.port = int(self.db.settings[self.hostname].BackendServerPort)
        if not self.port:
            raise MythDBError(MythError.DB_SETTING, 'BackendServerPort',
                                            self.port)

        self._ident = '%s:%d' % (self.host, self.port)
        if self._ident in self._shared:
            # existing connection found
            self._conn = self._shared[self._ident]
            if self.sendcommands:
                if self._conn.command is None:
                    self._conn.command = self._newcmdconn()
                elif self.blockshutdown:
                    # upref block of shutdown
                    # issue command to backend if needed
                    self._conn.blockshutdown += 1
                    if self._conn.blockshutdown == 1:
                        self._conn.command.blockShutdown()
            if self.receiveevents:
                if self._conn.event is None:
                    self._conn.event = self._neweventconn()
        else:
            # no existing connection, create new
            self._conn = self._ConnHolder()

            if self.sendcommands:
                self._conn.command = self._newcmdconn()
                if self.blockshutdown:
                    self._conn.blockshutdown = 1
            if self.receiveevents:
                self._conn.event = self._neweventconn()

            self._shared[self._ident] = self._conn
#.........这里部分代码省略.........

def ftopen(file, mode, forceremote=False, nooverwrite=False, db=None, \
                       chanid=None, starttime=None, download=False):
    """
    ftopen(file, mode, forceremote=False, nooverwrite=False, db=None)
                                        -> FileTransfer object
                                        -> file object
    Method will attempt to open file locally, falling back to remote access
            over mythprotocol if necessary.
    'forceremote' will force a FileTransfer object if possible.
    'file' takes a standard MythURI:
                myth://<group>@<host>:<port>/<path>
    'mode' takes a 'r' or 'w'
    'nooverwrite' will refuse to open a file writable,
                if a local file is found.
    """
    db = DBCache(db)
    log = MythLog('Python File Transfer', db=db)
    reuri = re.compile(\
        'myth://((?P<group>.*)@)?(?P<host>[\[\]a-zA-Z0-9_\-\.]*)(:[0-9]*)?/(?P<file>.*)')
    reip = re.compile('(?:\d{1,3}\.){3}\d{1,3}')

    if mode not in ('r','w'):
        raise TypeError("File I/O must be of type 'r' or 'w'")

    if chanid and starttime:
        protoopen = lambda host, file, storagegroup: \
                      RecordFileTransfer(host, file, storagegroup,\
                                         mode, chanid, starttime, db)
    elif download:
        protoopen = lambda host, lfile, storagegroup: \
                      DownloadFileTransfer(host, lfile, storagegroup, \
                                           mode, file, db)
    else:
        protoopen = lambda host, file, storagegroup: \
                      FileTransfer(host, file, storagegroup, mode, db)

    # process URI (myth://<group>@<host>[:<port>]/<path/to/file>)
    match = None
    try:
        match = reuri.match(file)
    except:
        pass

    if match:
        host = match.group('host')
        filename = match.group('file')
        sgroup = match.group('group')
        if sgroup is None:
            sgroup = 'Default'
    elif len(file) == 3:
        host, sgroup, filename = file
    else:
        raise MythError('Invalid FileTransfer input string: '+file)

    # get full system name
    host = host.strip('[]')
    if reip.match(host) or check_ipv6(host):
        host = db._gethostfromaddr(host)

    # user forced to remote access
    if forceremote:
        if (mode == 'w') and (filename.find('/') != -1):
            raise MythFileError(MythError.FILE_FAILED_WRITE, file,
                                'attempting remote write outside base path')
        if nooverwrite and FileOps(host, db=db).fileExists(filename, sgroup):
            raise MythFileError(MythError.FILE_FAILED_WRITE, file,
                                'refusing to overwrite existing file')
        return protoopen(host, filename, sgroup)

    if mode == 'w':
        # check for pre-existing file
        path = FileOps(host, db=db).fileExists(filename, sgroup)
        sgs = list(db.getStorageGroup(groupname=sgroup))
        if path is not None:
            if nooverwrite:
                raise MythFileError(MythError.FILE_FAILED_WRITE, file,
                                'refusing to overwrite existing file')
            for sg in sgs:
                if sg.dirname in path:
                    if sg.local:
                        return open(sg.dirname+filename, mode)
                    else:
                        return protoopen(host, filename, sgroup)

        # prefer local storage for new files
        for i,v in reversed(list(enumerate(sgs))):
            if not v.local:
                sgs.pop(i)
            else:
                st = os.statvfs(v.dirname)
                v.free = st[0]*st[3]
        if len(sgs) > 0:
            # choose path with most free space
            sg = sorted(sgs, key=lambda sg: sg.free, reverse=True)[0]
            # create folder if it does not exist
            if filename.find('/') != -1:
                path = sg.dirname+filename.rsplit('/',1)[0]
                if not os.access(path, os.F_OK):
                    os.makedirs(path)
            log(log.FILE, log.INFO, 'Opening local file (w)',
#.........这里部分代码省略.........