Why is SQLAlchemy 1.4.x not connecting to Heroku Postgres?

Issue

When using SQLAlchemy 1.4.x to connect to Heroku Postgres, I receive the following error:

sqlalchemy.exc.NoSuchModuleError: Can't load plugin: sqlalchemy.dialects:postgres

Resolution

SQLAlchemy 1.4.x has removed support for the postgres:// URI scheme, which is used by Heroku Postgres (https://github.com/sqlalchemy/sqlalchemy/issues/6083). To maintain compatibility, perform the following before setting up connections with SQLAlchemy:

import os

uri = os.getenv("DATABASE_URL")  # or other relevant config var
if uri.startswith("postgres://"):
    uri = uri.replace("postgres://", "postgresql://", 1)
# rest of connection code using the connection string `uri`

This will allow you to connect to Heroku Postgres services using SQLAlchemy >= 1.4.x