Locking a file in Python

Question

I need to lock a file for writing in Python. It will be accessed from multiple Python processes at once. I have found some solutions online, but most fail for my purposes as

Answer 1

I have been working on a situation like this where I run multiple copies of the same program from within the same directory/folder and logging errors. My approach was to write a "lock file" to the disc before opening the log file. The program checks for the presence of the "lock file" before proceeding, and waits for its turn if the "lock file" exists.

Here is the code:

def errlogger(error):

    while True:
        if not exists('errloglock'):
            lock = open('errloglock', 'w')
            if exists('errorlog'): log = open('errorlog', 'a')
            else: log = open('errorlog', 'w')
            log.write(str(datetime.utcnow())[0:-7] + ' ' + error + '\n')
            log.close()
            remove('errloglock')
            return
        else:
            check = stat('errloglock')
            if time() - check.st_ctime > 0.01: remove('errloglock')
            print('waiting my turn')

EDIT--- After thinking over some of the comments about stale locks above I edited the code to add a check for staleness of the "lock file." Timing several thousand iterations of this function on my system gave and average of 0.002066... seconds from just before:

lock = open('errloglock', 'w')

to just after:

remove('errloglock')

so I figured I will start with 5 times that amount to indicate staleness and monitor the situation for problems.

Also, as I was working with the timing, I realized that I had a bit of code that was not really necessary:

lock.close()

which I had immediately following the open statement, so I have removed it in this edit.