Python Postgresql

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Listtables = dbcursor.fetchall : The Python psycopg2 fetchall function returns all records returned from PostgreSQL. This recordset is stored in the Python list we are calling “listtables”.

Python Database PostgreSQL In this article you will learn how to use the PostgreSQL database with Python. PostgreSQL is an relational database management system (rdbms). PostgreSQL supports foreign keys, joins, views, triggers, stored procedures and much more. In this article. This tutorial shows how to deploy a data-driven Python Django web app to Azure App Service and connect it to an Azure Database for Postgres database. App Service provides a highly scalable, self-patching web hosting service. Nov 07, 2019 Psycopg is a PostgreSQL adapter for the Python programming language. This tool allows us to connect the capabilities of the Python language and libraries to obtain, manipulate, input, and update data stored in a PostgreSQL database. At the time of this writing the current version is psycopg2. PostgreSQL driver for Python — Psycopg Psycopg is the most popular PostgreSQL adapter for the Python programming language. Its core is a complete implementation of the Python DB API 2.0 specifications. Several extensions allow access to many of the features offered by PostgreSQL.

This PostgreSQL Python section shows you how to work with the PostgreSQL database using the Python programming language.

Python has various database drivers for PostgreSQL. Currently, the psycopg is the most popular PostgreSQL database adapter for the Python language. The psycopg fully implements the Python DB-API 2.0 specification.

The current version of the psycopg is 2 or psycopg2. The psycopg2 database adapter implemented in C as a libpq wrapper resulting in both fast and secure. The psycopg2 provides many useful features such as client-side and server-side cursors, asynchronous notification and communication, COPY command support, etc.

Besides, the psycopg2 driver supports many Python types out-of-the-box. The psycopg2 matches Python objects to the PostgreSQL data types, e.g., list to the array, tuples to records, and dictionary to hstore. If you want to customize and extend the type adaption, you can use a flexible object adaption system.

This PostgreSQL Python section covers the most common activities for interacting with PostgreSQL in Python application:

  • Connecting to the PostgreSQL database server – show you how to connect to the PostgreSQL database server from Python.
  • Creating new PostgreSQL tables in Python – show you how to create new tables in PostgreSQL from Python.
  • Inserting data into the PostgreSQL table in Python – explain to you how to insert data into a PostgreSQL database table in Python.
  • Updating data in the PostgreSQL table in Python – learn various ways to update data in the PostgreSQL table.
  • Transaction – show you how to perform transactions in Python.
  • Querying data from the PostgreSQL tables – walk you through the steps of querying data from the PostgreSQL tables in a Python application.
  • Calling a PostgreSQL function in Python – show you step by step how to call a PostgreSQL function in Python.
  • Calling a PostgreSQL stored procedure in Python – guide you on how to call a stored procedure from in a Python application.
  • Handling PostgreSQL BLOB data in Python– give you an example of inserting and selecting the PostgreSQL BLOB data in a Python application.
  • Deleting data from PostgreSQL tables in Python – show you how to delete data in a table in Python.

For demonstration purposes, we will use the suppliers sample database. The following picture illustrates the structure of the suppliers database:

The suppliers database has the following tables:

  1. vendors table: stores vendor data.
  2. parts table: stores parts data.
  3. parts_drawings table: stores the drawing of a part.
  4. vendor_parts table: stores the data of which parts supplied by which vendor.

Functions in PL/Python are declared via the standard CREATE FUNCTION syntax:

The body of a function is simply a Python script. When the function is called, its arguments are passed as elements of the list args; named arguments are also passed as ordinary variables to the Python script. Use of named arguments is usually more readable. The result is returned from the Python code in the usual way, with return or yield (in case of a result-set statement). If you do not provide a return value, Python returns the default None. PL/Python translates Python's None into the SQL null value.

For example, a function to return the greater of two integers can be defined as:

The Python code that is given as the body of the function definition is transformed into a Python function. For example, the above results in:

Python Postgresql Async

Python Postgresql

assuming that 23456 is the OID assigned to the function by PostgreSQL.

The arguments are set as global variables. Because of the scoping rules of Python, this has the subtle consequence that an argument variable cannot be reassigned inside the function to the value of an expression that involves the variable name itself, unless the variable is redeclared as global in the block. For example, the following won't work:

because assigning to x makes x a local variable for the entire block, and so the x on the right-hand side of the assignment refers to a not-yet-assigned local variable x, not the PL/Python function parameter. Using the global statement, this can be made to work:

Python Postgresql Display Console Message

But it is advisable not to rely on this implementation detail of PL/Python. It is better to treat the function parameters as read-only.