回调函数不被称为Python

我正在编写一个应用程序，它必须能够在python中监控文件系统目录的变化，为了做到这一点，我使用MacFSEvents，FSEvents C API上的python包装器，因为出于明显的效率原因，轮询不能作为一种选择，因为这段代码可以递归地监控大量文件，然而，模块确实可以工作，这样的代码会产生预期的结果

    from fsevents import Observer, Stream


def callback(FSEvent, mask=0, cookie=0):
        """
        the callback that gets called when an event occurs
        :param FSEvent: file or dir that originated the event
        :param mask: a bitMask that specifies the type of the event
        :param cookie: contains info to bind a moved_to to a moved_from event
        """
        print(FSEvent)
        print('\n')
        print(mask)
        print('\n')



if __name__ == "__main__":
    try:
        obs = Observer()
        obs.start()
        str = Stream(callback, "/Users/filipposavi/ass", file_events=True)
        obs.schedule(str)
    except KeyboardInterrupt:
        obs.stop()
        obs.join

但是，当我将其放入应该管理（相对）低级文件系统细节的类中时，回调不会被调用，下面您可以找到不起作用的代码

import hashlib
import os
import fsevents
from database import Db


BUFSIZE = 2 ** 3
chunksize = 1024


IN_CREATE = 0x00000100
IN_ATTRIB = 0x00000004
IN_MODIFY = 0x00000002
IN_DELETE = 0x00000200
IN_MOVED_FROM = 0x00000040
IN_MOVED_TO = 0x00000080


class FsCore(object):

    def __init__(self):
        self.db = Db()

    def callback(self, FSEvent, mask, cookie=0):
        """
        the callback that gets called when an event occurs
        :param FSEvent: file or dir that originated the event
        :param mask: a bitMask that specifies the type of the event
        :param cookie: contains info to bind a moved_to to a moved_from event
       """
        print('ciao')
        if (mask & IN_CREATE) == IN_CREATE:
            self.on_created(FSEvent)
        if (mask & IN_ATTRIB) == IN_ATTRIB:
            self.on_attrib(FSEvent)
        if (mask & IN_DELETE) == IN_DELETE:
            self.on_deleted(FSEvent)
        if (mask & IN_MODIFY) == IN_MODIFY:
            self.on_modified(FSEvent)
        if (mask & IN_MOVED_FROM) == IN_MOVED_FROM:
            self.on_moved(FSEvent, cookie, False)
        if (mask & IN_MOVED_TO) == IN_MOVED_TO:

    def startFSEvents(self, path):
        """

        :param path:
        """
        self.observer = fsevents.Observer()
        self.observer.start()
        self.stream = fsevents.Stream(self.callback, path, file_events=True)
        self.observer.schedule(self.stream)

    def stopFSEvents(self):
        """


        """
        self.observer.unschedule(self.stream)
        self.observer.join()
        self.observer.stop()

下面是触发事件/回调（单元测试的一部分）的代码

希望你们能给我一个正确的方向，因为我对python有点生疏，所以我非常坚持这个方向

    self.fs = FsCore()
    self.fs.startFSEvents(self.path)
    self.database = Db()
    path = self.path + "/tmp"
    file = open(path, mode='a')
    file.write("ciao")
    file.flush()
    file.close()
    if not self.database.getFile(path):
        self.fail("onCreated callback doesn't works or it's not called at all")