Delete log file if it is empty after being closed

Question

I have a library function that launches a generic background process and logs it.

def LaunchAndLog(cmd):
    cmd_args = cmd.split() # Split arguments into array
    logfile = cmd_args[0] + '.log'
    with open(logfile,'w') as log:
        return subprocess.Popen(cmd_args, stdout=log,stderr=log)

Main question: Is it possible to revise this function so that upon the log file being closed, if it is empty it is deleted automatically?

Note: I want a solution where I can call this function and forget it. I don't want to have to remember to call a cleanup function every time after the job ends.

(Rejected?) Idea: I can use threading to launch a separate thread that monitors the process and/or log file, but this seems more complicated than necessary.

Note: Must work in Python 2.7, but I'm also interested in a Python 3 solution, if it's simpler.

mhlester · Accepted Answer · 2014-01-10 00:15:50Z

3

Try reversing the concept, and only create the file when you're ready to write. Create your own class to handle the file object:

class MyFile():
    def __enter__(self):
        return self

    def __init__(self, path):
        ''' store the path, but don't actually open the file '''
        self.path = path
        self.file_object = None

    def write(self, s):
        ''' you open the file here, just before writing '''
        if not self.file_object:
            self.file_object = open(self.path, 'w')
        self.file_object.write(self, s)

    def close(self):
        ''' close the file '''
        if self.file_object:
            self.file_object.close()

    def __exit__(self, exc_type, exc_value, exc_traceback):
        self.close()

Then your with statement becomes this:

with MyFile(logfile) as log:

Proposed but rejected edit from supergra manually incorporated

edited Jan 10, 2014 at 0:15

answered Jan 9, 2014 at 18:59

mhlester

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3 Comments

supergra Over a year ago

This does not quite work as written. It needs an __enter__ function and the __exit__ function needs to accept 4 arguments, not 1. See here for an edit: stackoverflow.com/review/suggested-edits/3772114 which was helpfully rejected by the SO goons.

supergra Over a year ago

Sorry, one more problem I've run into. You need to define a fileno() function in the class. I did this: def fileno(self): if self.file_object: return self.file_object.fileno() else: return None. Perhaps there's a better way.

mhlester Over a year ago

@user2066480, __exit__() calls close(). can't edit that out

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