Shubham Ankit

Shubham Ankit

1563161597

Using PostgreSQL Database with Python

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.

Requirement:

Create a virtual environment using python 3 and activate it. Install below packages.

psycopg2==2.7.3.2

Installation:

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 10.3.

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

Creating database:

Before creating a new database, lets list all the databases. Use \l or \list for the same.

To create database, exit the psql terminal by typing \q and use command createdb testdb.

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 \c or \connect and database name. \c testdb in this case.

Creating Table:

Most the query sytanx in PostgreSQL are same as MySQL.

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 \d.

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.

Connecting from Python Script:

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

Inserting Data into Table:

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()[0]
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.

Fetching Data from Table:

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

Updating a row:

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 \q command.

If you are facing any issue, feel free to comment.

#python #postgresql #web-development

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Using PostgreSQL Database with Python
Ray  Patel

Ray Patel

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top 30 Python Tips and Tricks for Beginners

Welcome to my Blog , In this article, you are going to learn the top 10 python tips and tricks.

1) swap two numbers.

2) Reversing a string in Python.

3) Create a single string from all the elements in list.

4) Chaining Of Comparison Operators.

5) Print The File Path Of Imported Modules.

6) Return Multiple Values From Functions.

7) Find The Most Frequent Value In A List.

8) Check The Memory Usage Of An Object.

#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

Ray  Patel

Ray Patel

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Lambda, Map, Filter functions in python

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

Kaia  Schmitt

Kaia Schmitt

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How to Create Table in SQLite Database Python | Python Built-In Database - III

Create Table - Python Built-In Database - SQLite.

Github - https://github.com/theindianinnovation/Python-SQLite-Database-Tutorial

#sqlite #database #python #sqlite database python #database python

Kaia  Schmitt

Kaia Schmitt

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How to Insert Records in SQLite Database Python | Python Built-In Database - IV

Insert Records - Python Built-In Database - SQLite.

Github - https://github.com/theindianinnovation/Python-SQLite-Database-Tutorial

#database #python #sqlite database python #sqlite #database python

How To Compare Tesla and Ford Company By Using Magic Methods in 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.

1. init

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

2. add

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