Consider the following code:

import logging
import logging.handlers

if __name__ == "__main__":
    fh = logging.handlers.RotatingFileHandler("log.txt")
    mh = logging.handlers.MemoryHandler(1024, 
logging.ERROR, fh)
    logging.getLogger().addHandler(mh)
    logging.getLogger().warning("next statement crashes")
    logging.shutdown()

which results in a crash due to operating on a closed 
file. The reason is that the shutdown flushes and closes 
all handlers in undefined order. In above case, first 
the 'fh' handlers is flushes and closed then the 'mh' 
handler.

The solution is to first flush all handlers times the 
number of handlers before closing them. Thus (omitting 
error handling):

def shutdown():
    for i in range(len(_handlers)):
        for h in _handlers.keys():
            h.flush()
    for h in _handlers.keys():
        h.close()