# PostgreSQL Connection

1. Install Module:

```bash
pip install psycopg2
```

2\. Connection string:

```python
conn = psycopg2.connect("dbname=suppliers user=postgres password=postgres")
```

or use as a list:

```python
conn = psycopg2.connect(
    host="localhost",
    database="suppliers",
    user="postgres",
    password="Abcd1234")
```

To make it more convenient, you can use a configuration file to store all connection parameters. The following shows the contents of the `database.ini` file:

```python
[postgresql]
host=localhost
database=suppliers
user=postgres
password=SecurePas$1
```

By using the database.ini, you can change the PostgreSQL connection parameters when you move the code to the production environment without modifying the code.

Notice that if you git, you need to add the database.ini to the .gitignore file to not committing the sensitive information to the public repo like github. The .gitignore file will be like this:

```bash
database.ini
```

The following `config()` function read the `database.ini` file and returns connection parameters. The `config()` function is placed in the `config.py` file:

```python
#!/usr/bin/python
from configparser import ConfigParser


def config(filename='database.ini', section='postgresql'):
    # create a parser
    parser = ConfigParser()
    # read config file
    parser.read(filename)

    # get section, default to postgresql
    db = {}
    if parser.has_section(section):
        params = parser.items(section)
        for param in params:
            db[param[0]] = param[1]
    else:
        raise Exception('Section {0} not found in the {1} file'.format(section, filename))

    return db
```

The following `connect()` function connects to the suppliers database and prints out the `PostgreSQL database version`

```python
#!/usr/bin/python
import psycopg2
from config import config

def connect():
    """ Connect to the PostgreSQL database server """
    conn = None
    try:
        # read connection parameters
        params = config()

        # connect to the PostgreSQL server
        print('Connecting to the PostgreSQL database...')
        conn = psycopg2.connect(**params)
		
        # create a cursor
        cur = conn.cursor()
        
	# execute a statement
        print('PostgreSQL database version:')
        cur.execute('SELECT version()')

        # display the PostgreSQL database server version
        db_version = cur.fetchone()
        print(db_version)
       
	# close the communication with the PostgreSQL
        cur.close()
    except (Exception, psycopg2.DatabaseError) as error:
        print(error)
    finally:
        if conn is not None:
            conn.close()
            print('Database connection closed.')


if __name__ == '__main__':
    connect()
```

How it works:

* First, read database connection parameters from the `database.ini` file.
* Next, create a new database connection by calling the `connect()` function.
* Then, create a new `cursor` and `execute` an `SQL` statement to get the PostgreSQL database version.
* After that, read the result set by calling the `fetchone()` method of the cursor object.
* Finally, `close` the `communication` with the `database` server by calling the `close()` method of the cursor and connection objects.