Introduction to cx_Oracle

cx_Oracle is a Python extension module that enables Python access to Oracle Database. It conforms to the Python Database API v2.0 Specification with a considerable number of additions and a couple of exclusions.


Python programs call cx_Oracle functions. Internally cx_Oracle dynamically loads Oracle Client libraries to access Oracle Database. The database can be on the same machine as Python, or it can be remote.


Fig. 1 cx_Oracle Architecture

cx_Oracle is typically installed from PyPI using pip. The Oracle Client libraries need to be installed separately. The libraries can be obtained from an installation of Oracle Instant Client, from a full Oracle Client installation, or even from an Oracle Database installation (if Python is running on the same machine as the database).

Some behaviors of the Oracle Client libraries can optionally be configured with an oraaccess.xml file, for example to enable auto-tuning of a statement cache. See Optional Oracle Client Configuration Files.

The Oracle Net layer can optionally be configured with files such as tnsnames.ora and sqlnet.ora, for example to enable network encryption. See Optional Oracle Net Configuration Files.

Oracle environment variables that are set before cx_Oracle first creates a database connection will affect cx_Oracle behavior. Optional variables include NLS_LANG, NLS_DATE_FORMAT and TNS_ADMIN. See Oracle Environment Variables.


The cx_Oracle feature highlights are:

  • Easily installed from PyPI
  • Support for multiple Oracle Client and Database versions
  • Execution of SQL and PL/SQL statements
  • Extensive Oracle data type support, including large objects (CLOB and BLOB) and binding of SQL objects
  • Connection management, including connection pooling
  • Oracle Database High Availability features
  • Full use of Oracle Network Service infrastructure, including encrypted network traffic and security features

A complete list of supported features can be seen here.

Getting Started

Install cx_Oracle using the installation steps.

Create a script as shown below:


import cx_Oracle

# Establish the database connection
connection = cx_Oracle.connect("hr", userpwd, "")

# Obtain a cursor
cursor = connection.cursor()

# Data for binding
managerId = 145
firstName = "Peter"

# Execute the query
sql = """SELECT first_name, last_name
         FROM employees
         WHERE manager_id = :mid AND first_name = :fn"""
cursor.execute(sql, mid = managerId, fn = firstName)

# Loop over the result set
for row in cursor:

This uses Oracle’s sample HR schema.

Simple connection to the database requires a username, password and connection string. Locate your Oracle Database user name and password and the database connection string, and use them in For cx_Oracle the connection string is commonly of the format hostname/servicename, using the host name where the database is running and the Oracle Database service name of the database instance.

The cursor is the object that allows statements to be executed and results (if any) fetched.

The data values in managerId and firstName are ‘bound’ to the statement placeholder ‘bind variables’ :mid and :fn when the statement is executed. This separates the statement text from the data, which helps avoid SQL Injection security risks. Binding is also important for performance and scalability.

The cursor allows rows to be iterated over and displayed.

Run the script:


The output is:

('Peter', 'Hall')
('Peter', 'Tucker')

Examples and Tutorials

Runnable examples are in the GitHub samples directory. A Python cx_Oracle tutorial is also available.