How can I log exception errors to disk of a systemd service? - gunicorn

Question

I have written below systemd service that runs the flask app on gunicorn following a tutorial.
I am able to see access logs in /var/log/nginx/ but not log of error happening in the python flask app!
How can I log errors to disk of a systemd service?
$ cat /etc/systemd/system/gunicorn.service [Unit]
Description=gunicorn daemon for /var/www/html/start_backend.py
After=network.target
[Service]
PermissionsStartOnly = true
User=ciasto
Group=www-data
RuntimeDirectory=gunicorn
WorkingDirectory=/var/www/html/
ExecStartPre = /bin/chown -R pi:www-data /var/www/html/
Environment="APP_SETTINGS=production"
Environment="DB_USER=username"
Environment="DB_PWD=password"
Environment="DB_HOST="ceres.local"
ExecStart=/usr/bin/env gunicorn --bind=unix:/tmp/gunicorn.sock --workers=4 start_backend:web_app
ExecReload=/bin/kill -s HUP $MAINPID
ExecStop=/bin/kill -s TERM $MAINPID
[Install]
WantedBy=multi-user.target
To get exception error logs I added below two lines:
StandardOutput=file:/var/log/gunicorn/log1.log
StandardError=file:/var/log/gunicorn/log2.log
I restarted the gunicorn service than visited the URL to throw the exception error, check the path where I expect log to come . But I see nothing
sudo systemctl status gunicorn ● gunicorn.service - gunicorn daemon for /var/www/html/start_backend.py
Loaded: loaded (/etc/systemd/system/gunicorn.service; enabled; vendor preset: enabled)
Active: active (running) since Thu 2019-01-03 22:42:31 IST; 1min 9s ago
Process: 3944 ExecStop=/bin/kill -s TERM $MAINPID (code=exited, status=0/SUCCESS)
Process: 3947 ExecStartPre=/bin/chown -R ciasto:www-data /var/www/html/ (code=exited, status=0/SU Main PID: 3950 (gunicorn)
CGroup: /system.slice/gunicorn.service
├─3950 /usr/bin/python /usr/bin/gunicorn --bind=unix:/tmp/gunicorn.sock --workers=4 ├─3965 /usr/bin/python /usr/bin/gunicorn --bind=unix:/tmp/gunicorn.sock --workers=4 ├─3966 /usr/bin/python /usr/bin/gunicorn --bind=unix:/tmp/gunicorn.sock --workers=4 ├─3967 /usr/bin/python /usr/bin/gunicorn --bind=unix:/tmp/gunicorn.sock --workers=4 └─3968 /usr/bin/python /usr/bin/gunicorn --bind=unix:/tmp/gunicorn.sock --workers=4
Jan 03 22:43:34 ceres env[3950]: db.connect()
Jan 03 22:43:34 ceres env[3950]: File "/home/ciasto/.local/lib/python2.7/site-packages/peewee.py"Jan 03 22:43:34 ceres env[3950]: self._state.set_connection(self._connect())
Jan 03 22:43:34 ceres env[3950]: File "/home/ciasto/.local/lib/python2.7/site-packages/peewee.py"Jan 03 22:43:34 ceres env[3950]: return mysql.connect(db=self.database, **self.connect_paraJan 03 22:43:34 ceres env[3950]: File "/home/ciasto/.local/lib/python2.7/site-packages/MySQLdb/__Jan 03 22:43:34 ceres env[3950]: return Connection(*args, **kwargs)
Jan 03 22:43:34 ceres env[3950]: File "/home/ciasto/.local/lib/python2.7/site-packages/MySQLdb/coJan 03 22:43:34 ceres env[3950]: super(Connection, self).__init__(*args, **kwargs2)
Jan 03 22:43:34 ceres env[3950]: TypeError: connect() argument 1 must be string, not None
ciasto#ceres:/etc/systemd/system $ cd /var/log/gunicorn ciasto#ceres:/var/log/gunicorn $ ll
total 0
ciasto#ceres:/var/log/gunicorn $