Delete existing file after successful write

Question

I am performing a daily database dump in a python script and I am looking for the most python efficient way to delete the current file only after the recent one was written successfully, i.e. delete the backup-12-11-2019.sql only after backup-13-11-2019 was created successfully

Answer 1

you can use try:...except:...esle: as the following code.

import datetime
import os
now = datetime.datetime.utcnow()
try:
    pg_dumpall('-h', DB_HOST, '-U', DB_USERNAME, '-p', DB_PORT, _out=BACKUP_FOLDER + 'backup-' + str(now.day) + '-' + str(now.month) + '-' + str(now.year) + '.sql')
except Exception as e:
    print(e)
else:
    previous_day = now - datetime.timedelta(days=1)
    os.remove(BACKUP_FOLDER + 'backup-' + str(now.day - 1) + '-' + str(now.month) + '-' + str(now.year) + '.sql')

If the pg_dumpall does not raise and Exception it will delete the previous backup file

Best regard

Answer 2

From DBA StackExchange

    pg_dumpall -U pg_user > /tmp/tmp.txt
    DUMP_STATUS=$?
    echo "Dump status: $DUMP_STATUS" > /tmp/status.txt

And SO: Get return value

    subprocess.check_output([SCRIPT, "-d", date], shell=True).

We're able to come up with something that will run the command you want to run, and check its return value at the same time.

    output = subprocess.check_output(['pg_dumpall', '-h', DB_HOST, '-U', DB_USERNAME, '-p', DB_PORT], stdout=outfile)
    if output == 0:
        print("Success")
        os.remove(oldfile)
    else:
        print("Failure")