Python - PostgreSQL multiple DB backup script

pg_backup.py

import psycopg2
import time
import subprocess
import os
import glob

USER = "username"
PASS = "password"
HOST = "host"
DBNAME = "dbname"
BACKUP_DIR = "w:\\backups\\"

db_dumper = """ "c:\\program files\\PostgreSQL\\9.6\\bin\\pg_dump" -U %s -Z 9 -f %s -F c %s  """
users_dumper = """ "c:\\program files\\PostgreSQL\\9.6\\bin\\pg_dumpall" -U %s --globals-only -f %s """

# Log every action into the LOG file
def log(string):
    path = BACKUP_DIR + '\\backup.log'
    with open(path,'a') as log_file:
        log_file.write(time.strftime("%Y-%m-%d-%H-%M-%S", time.gmtime()) + ": " + str(string) + '\n')
        log_file.close()
    
# Define number of days the backups will be stored in BACKUP_DIR (in this case set to 7 days)
days = time.time() - ( 60 * 60 * 24 * 7 )
 
os.putenv('PGPASSWORD', PASS)

conn_string = "host=" + HOST + " dbname=" + DBNAME + " user=" + USER + " password=" + PASS
conn = psycopg2.connect(conn_string)
curs = conn.cursor()
curs.execute("select datname from pg_database")
dbs = curs.fetchall()
database_list = []

# Define databases to backup
for db in dbs:
    if str(db[0]) == "DB1" or str(db[0]) == "DB2":
        database_list.append(str(db[0]))
 
# Delete old backup files first.
for database_name in database_list : 
    glob_list = glob.glob(BACKUP_DIR + database_name + '*' + '.backup')
    for file in glob_list:
        file_info = os.stat(file)
        if file_info.st_ctime < days:
            log("Deleting: %s" % file)
            os.unlink(file)
        else:
            log("Keeping: %s" % file)
 
log("Backup files older than %s were deleted." % time.strftime('%c', time.gmtime(x_days_ago)))

# Now perform the backup.
for database_name in database_list :
    log("dump started for %s" % database_name)
    thetime = time.strftime("%Y-%m-%d-%H-%M")
    db_file_name = database_name + "_" + thetime + ".backup"
    users_file_name = "GLOBALS" + "_" + thetime + ".backup"
    
    #Run the pg_dump command to get the DB backups
    db_dump = db_dumper % (USER,  BACKUP_DIR + db_file_name, database_name)
    log(db_dump)
    subprocess.call(db_dump,shell = True)
    
    log("dump finished for %s" % database_name)
    
#Run the pg_dump command to the GLOBALs (users, groups, tablespaces) backup
log("dump started for GLOBALs")
users_dump = users_dumper % (USER,  BACKUP_DIR + users_file_name)
log(users_dump)
subprocess.call(users_dump,shell = True)
log("dump finished for GLOBALs")
 
log("Backup job complete.")