Python shelve module question

Question

Does the Python shelve module have any protection built in to make sure two processes aren\'t writing to a file at the same time?

Answer 1

As per the top answer, it's not safe to have multiple writers to the shelve. My approach to making shelves safer is to write a wrapper that takes care of opening and accessing shelve elements. The wrapper code looks something like this:

def open(self, mode=READONLY):
    if mode is READWRITE:
        lockfilemode = "a" 
        lockmode = LOCK_EX
        shelve_mode = 'c'
    else:
        lockfilemode = "r"
        lockmode = LOCK_SH
        shelve_mode = 'r'
    self.lockfd = open(shelvefile+".lck", lockfilemode)
    fcntl.flock(self.lockfd.fileno(), lockmode | LOCK_NB)
    self.shelve = shelve.open(shelvefile, flag=shelve_mode, protocol=pickle.HIGHEST_PROTOCOL))
def close(self):
    self.shelve.close()
    fcntl.flock(self.lockfd.fileno(), LOCK_UN)
    lockfd.close()