In this article we will see how to connect to PostgreSQL from Python Script and perform queries.
PostgreSQL is an open source object-relational database management system. PostgreSQL is ACID-compliant and is transactional. It has triggers, foreign keys and supports functions and stored procedures.
PostgreSQL is used by giants like Uber, Apple, Netflix and Instagram.
Create a virtual environment using python 3 and activate it. Install below packages.
Install the PostgreSQL database and utilities using below commands.
sudo apt-get update sudo apt-get install postgresql postgresql-contrib
By default, PostgreSQL sets up the user and database “postgres” upon a new installation. We need to switch to this user to use postgres database.
sudo -su postgres
Now go to the Postgres prompt by typing
psql on terminal.
We are using version
If you get any error in connecting to database, make sure PostgreSQL is running. Check the status using below command.
$ systemctl status postgresql
You can check for errors in logs using below command.
$ tail -f /var/log/postgresql
Before creating a new database, lets list all the databases. Use
\list for the same.
To create database, exit the psql terminal by typing
\q and use command
postgres@brahma:~$ createdb testdb postgres@brahma:~$ psql psql (10.3 (Ubuntu 10.3-1.pgdg16.04+1)) Type "help" for help. postgres=# \l List of databases Name | Owner | Encoding | Collate | Ctype | Access privileges ---------------+----------+----------+---------+-------+----------------------- postgres | postgres | UTF8 | en_IN | en_IN | rana_test | postgres | UTF8 | en_IN | en_IN | template0 | postgres | UTF8 | en_IN | en_IN | =c/postgres + | | | | | postgres=CTc/postgres template1 | postgres | UTF8 | en_IN | en_IN | =c/postgres + | | | | | postgres=CTc/postgres testdb | postgres | UTF8 | en_IN | en_IN | (5 rows) postgres=# \c testdb You are now connected to database "testdb" as user "postgres". testdb=#
To connect to another database, use command
\connect and database name.
\c testdb in this case.
create table users ( id serial PRIMARY KEY, username varchar (20) NOT NULL, age smallint NOT NULL, location varchar (50) NOT NULL );
Copy paste the above sytax in terminal and new table will be created. You can list the tables by typing
testdb=# create table users ( testdb(# username varchar (20) NOT NULL, testdb(# age smallint NOT NULL, testdb(# location varchar (50) NOT NULL testdb(# ); CREATE TABLE testdb=# \d List of relations Schema | Name | Type | Owner --------+-------+-------+---------- public | users | table | postgres (1 row) testdb=#
You can learn more about querying from psql terminal by visitng official site. Lets go to Python code.
We installed the psycopg package in virtual environment. Use below code in Python Script to connect to database.
import psycopg2 # this function will return the connection object def connect(): conn = None try: conn = psycopg2.connect(host="localhost", user="postgres", password="root", database="testdb") except Exception as e: print(repr(e)) return conn
First get the connection and cursor and then create query. Once query is executed, commit using connection and close the cursor and connection.
conn = connect() cur = conn.cursor() last_insert_id = None # inserting data in users table sql_query = "insert into users (username, age, location) values (%s, %s, %s) returning id;" sql_data = ( "Ajay", "25", "New York" ) cur.execute(sql_query, sql_data) last_insert_id = cur.fetchone() print("Last Insert ID " + str(last_insert_id)) conn.commit() cur.close() conn.close() return last_insert_id
We are Inserting data in table and returning the primary key
id which is the serial key.
Select query for PostgreSQL is same as MySQL.
conn = connect() cur = conn.cursor() sql_query = "select username, age, location from users where location = %s;" sql_data = ("Delhi") cur.execute(sql_query, sql_data) results = cur.fetchall() return results
conn = connect() cursor = conn.cursor() sql_query = "update users set location = %s where username = %s;" sql_data = ("Mumbai", "Ajay") cursor.execute(sql_query, sql_data) cursor.close() conn.close() return True
To exit the terminal use
If you are facing any issue, feel free to comment.
#python #postgresql #web-development
Welcome to my Blog , In this article, you are going to learn the top 10 python tips and tricks.
#python #python hacks tricks #python learning tips #python programming tricks #python tips #python tips and tricks #python tips and tricks advanced #python tips and tricks for beginners #python tips tricks and techniques #python tutorial #tips and tricks in python #tips to learn python #top 30 python tips and tricks for beginners
Welcome to my Blog, In this article, we will learn python lambda function, Map function, and filter function.
Lambda function in python: Lambda is a one line anonymous function and lambda takes any number of arguments but can only have one expression and python lambda syntax is
Syntax: x = lambda arguments : expression
Now i will show you some python lambda function examples:
#python #anonymous function python #filter function in python #lambda #lambda python 3 #map python #python filter #python filter lambda #python lambda #python lambda examples #python map
Create Table - Python Built-In Database - SQLite.
#sqlite #database #python #sqlite database python #database python
Insert Records - Python Built-In Database - SQLite.
#database #python #sqlite database python #sqlite #database python
Magic Methods are the special methods which gives us the ability to access built in syntactical features such as ‘<’, ‘>’, ‘==’, ‘+’ etc…
You must have worked with such methods without knowing them to be as magic methods. Magic methods can be identified with their names which start with __ and ends with __ like init, call, str etc. These methods are also called Dunder Methods, because of their name starting and ending with Double Underscore (Dunder).
Now there are a number of such special methods, which you might have come across too, in Python. We will just be taking an example of a few of them to understand how they work and how we can use them.
class AnyClass: def __init__(): print("Init called on its own") obj = AnyClass()
The first example is _init, _and as the name suggests, it is used for initializing objects. Init method is called on its own, ie. whenever an object is created for the class, the init method is called on its own.
The output of the above code will be given below. Note how we did not call the init method and it got invoked as we created an object for class AnyClass.
Init called on its own
Let’s move to some other example, add gives us the ability to access the built in syntax feature of the character +. Let’s see how,
class AnyClass: def __init__(self, var): self.some_var = var def __add__(self, other_obj): print("Calling the add method") return self.some_var + other_obj.some_var obj1 = AnyClass(5) obj2 = AnyClass(6) obj1 + obj2
#python3 #python #python-programming #python-web-development #python-tutorials #python-top-story #python-tips #learn-python