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Does anyone know how to connect a PostgreSQL database to a Datalore notebook?

I'm working in Datalore (a jupyter notebook IDE) and I'm trying to connect to a postgresql (version 14) table via the following line of code.
df = pd.read_sql_table('emp','postgresql://{username}:{password}#localhost:5432/postgres')
where username and password are supplied in my notebook.
This gives the following error message:
OperationalError: (psycopg2.OperationalError) connection to server at "localhost" (127.0.0.1), port 5432 failed: Connection refused Is the server running on that host and accepting TCP/IP connections? connection to server at "localhost" (::1), port 5432 failed: Cannot assign requested address Is the server running on that host and accepting TCP/IP connections? (Background on this error at: https://sqlalche.me/e/14/e3q8)
When trying to test the connection to my database from the Datalore side pane, I get the following error message:
Connection to localhost:5432 refused. Check that the hostname and port are correct and that the postmaster is accepting TCP/IP connections.
I have already altered the IP address in pg_hba.conf from 127.0.0.0/32 to 0.0.0.0/0. Additionally, I have checked postgresql.conf and the listen_addresses = '*'.
My thoughts are that localhost shouldn't be used or that postmaster needs to be reset. If I am correct:
What should be used instead of localhost, and where do I find the correct hostname
How do I reset postmaster (I manually installed postgresql, I did not use Homebrew).
Is there anything else I haven't considered?

Establishing SSH connection using Python

This is the first time I'm asking a question on stackoverflow, so do inform me if I should ask questions differently or provide additional data.
I have an ssh command that I run on my command prompt to connect to postgreSQL server
ssh -L 5433:<host>:5432 -i <public_key> <username>#<IP address> -p 1024 -N
I try run the same through a python script, when I run it using
os.system("ssh -L 5433:<host>:5432 -i <public_key> <username>#<IP address> -p 1024 -N")
conn1 = None
conn1 = psycopg2.connect(dbname="db",user="username",
host="localhost", password="xxxx",port="5433")
It throws me the following error,
could not connect to server: Connection refused (0x0000274D/10061)
Is the server running on host "localhost" (::1) and accepting
TCP/IP connections on port 5433?
I have tried using paramiko to connect to the same, but I'm unable to translate the command line that I have to all the parameters required, for example, I don't understand port1:xxx:port2 and how to implement that in paramiko, the same goes for the public key. Given below is the code I use for that,
import paramiko
ssh = paramiko.SSHClient()
ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
ssh.connect('<hostname>', username='<username>, key_filename='<public_key>')
I've looked through many documentations but can't find a solution to the same. Any help is massively appreciated.

Heroku refuses connection to postgres database

I am trying to deploy my Flask app based on PostgreSQL on Heroku, but I when I try to create the table with db.create_all() I keep getting this error:
(psycopg2.OperationalError) could not connect t
rver: Connection refused
Is the server running on host "localhost" (127.0.0.1) and accepting
TCP/IP connections on port 5432?
Here is how my code looks like:
app=Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI']='postgres://kfgriimpfjecsv:Bk1*****G#localhost:5432/dd71doth8gopgh'
db=SQLAlchemy(app)
if __name__ == '__main__':
app.debug=True
app.run()
I am using Heroku Toolbelt to communicate with Heroku servers. Also, when I try this:
psql -p 5432 -h localhost
I get almost the same error:
psql: could not connect to server: Connection refused
Is the server running on host "localhost" (127.0.0.1) and accepting
TCP/IP connections on port 5432?
I also tried ec2-23-21-215-184.compute-1.amazonaws.com instead of localhost in the URI, but got the same error.
And here is the complete traceback that I get when I run db.create_all():
Any idea why the connection is being refused and how to solve this?

It seems I had to append a sslmode parameter to the database URI, so changing the second line to the following solved the problem:
app.config['SQLALCHEMY_DATABASE_URI']= "postgresql+psycopg2://kfgriimpfjecsv:Bk1*******G#ec2-23-21-215-184.compute-1.amazonaws.com:5432/dd71doth8gopgh?sslmode=require"

Failed to run python manage.py migrate command on AWS Elastic Beanstalk instance manually

I have created the project with command
:: eb create --database.engine postgres --region ap-southeast-1.
It shows that my deployment is successful.
Also when I run command :: eb open, it successfully open my project website.
Also when I checked eb-activity logs on my instance at /var/log/eb-activity.log, it also shows migration successful when I deployed my project.
But When I tried to run $ python manage.py migrate manually on Elastic Beanstalk instance it gives error,
django.db.utils.OperationalError: could not connect to server: Connection refused
Is the server running on host "localhost" (127.0.0.1) and accepting
TCP/IP connections on port 5432?
Also when I tried to create a user manually on python manage.py shell. It again gives error,
django.db.utils.OperationalError: could not connect to server: Connection refused
Is the server running on host "localhost" (127.0.0.1) and accepting
TCP/IP connections on port 5432?
I want to access postgres database on elastikbeanstalk instance and want to use commands
$ python manage.py migrate.
Is there a way to do that?

Connection Error while connecting to PostgreSQL as postgres user?

I am not able connect to PostgreSQL remotely using python and psycopg2:
Here is my code.
>>> import psycopg2
>>> conn_string = "host='localhost' dbname='mydb' user='postgres'"
>>> print "Connecting to database\n ->%s" % (conn_string)
Connecting to database
->host='localhost' dbname='mydb' user='postgres'
>>> conn = psycopg2.connect(conn_string)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/tools/lib/python2.7/site-packages/psycopg2/__init__.py", line 164, in connect
conn = _connect(dsn, connection_factory=connection_factory, async=async)
psycopg2.OperationalError: could not connect to server: Connection refused
Is the server running on host "localhost" (::1) and accepting
TCP/IP connections on port 5432?
could not connect to server: Connection refused
Is the server running on host "localhost" (127.0.0.1) and accepting
TCP/IP connections on port 5432?
The password is not set for postgres user.
Generally, I can connect to database by running following method on host.
1. SSH to box
2. su - postgres
3. psql
4. \c mydb
The server runs PostgreSQL 9.1.

You're trying to connect to PostgreSQL on localhost using a script running on your computer, but there's no PostgreSQL server running there.
For this to work, you'd have to ssh to the remote server, then run your Python script there, where the PostgreSQL server is "local" relative to the Python script.
(That's why running psql works - because you're running it on the remote server, where PostgreSQL is "local" relative to psql).
Alternately, you could:
Use an SSH tunnel to forward the PostgreSQL port from the local computer to the remote one; or
Connect directly over TCP/IP to the remote PostgreSQL server using its host name or IP address, after enabling remote connections on the server.
Note that just putting the server's IP address or host name into the connection string instead of localhost will not work unless you also configure the server to accept remote connections. You must set listen_addresses to listen for non-local connections, add any required firewall rules, set pg_hba.conf to permit connections from remote machines, and preferably set up SSL. All this is covered in the Client Authentication chapter of the PostgreSQL user manual.
You'll probably find an SSH tunnel simpler and easier to understand.