Python and Oracle Database Tutorial: Scripting for the Future

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Contents

Overview

This tutorial is an introduction to using Python with Oracle Database. It contains beginner and advanced material. Sections can be done in any order. Choose the content that interests you and your skill level. The tutorial has scripts to run and modify, and has suggested solutions.

Python is a popular general purpose dynamic scripting language. The cx_Oracle interface provides the Python API to access Oracle Database.

If you are new to Python review the Appendix: Python Primer to gain an understanding of the language.

When you have finished this tutorial, we recommend reviewing the cx_Oracle documention.

The original copy of these instructions that you are reading is here.

cx_Oracle Architecture

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. If the database is local, the client libraries from the Oracle Database software installation can be used.

Python cx_Oracle architecture

Setup

1. Connecting to Oracle

You can connect from Python to a local, remote or cloud database. Documentation link for further reading: Connecting to Oracle Database.

2. Connection Pooling

Connection pooling is important for performance in when multi-threaded applications frequently connect and disconnect from the database. Pooling also gives the best support for Oracle high availability features. Documentation link for further reading: Connection Pooling.

3. Fetching Data

Executing SELECT queries is the primary way to get data from Oracle Database. Documentation link for further reading: SQL Queries.

4. Binding Data

Bind variables enable you to re-execute statements with new data values without the overhead of re-parsing the statement. Binding improves code reusability, improves application scalability, and can reduce the risk of SQL injection attacks. Using bind variables is strongly recommended. Documentation link for further reading: Using Bind Variables.

5. PL/SQL

PL/SQL is Oracle's procedural language extension to SQL. PL/SQL procedures and functions are stored and run in the database. Using PL/SQL lets all database applications reuse logic, no matter how the application accesses the database. Many data-related operations can be performed in PL/SQL faster than extracting the data into a program (for example, Python) and then processing it. Documentation link for further reading: PL/SQL Execution.

6. Type Handlers

Type handlers enable applications to alter data that is fetched from, or sent to, the database. Documentation links for further reading: Changing Fetched Data Types with Output Type Handlers and Changing Bind Data Types using an Input Type Handler.

7. LOBs

Oracle Database "LOB" long objects can be streamed using a LOB locator, or worked with directly as strings or bytes. Documentation link for further reading: Using CLOB and BLOB Data.

8. Rowfactory functions

Rowfactory functions enable queries to return objects other than tuples. They can be used to provide names for the various columns or to return custom objects.

9. Subclassing connections and cursors

Subclassing enables application to "hook" connection and cursor creation. This can be used to alter or log connection and execution parameters, and to extend cx_Oracle functionality. Documentation link for further reading: Tracing SQL and PL/SQL Statements.

10. Advanced Queuing

Oracle Advanced Queuing (AQ) allows messages to be passed between applications. Documentation link for further reading: Oracle Advanced Queuing (AQ).

11. Simple Oracle Document Access (SODA)

Simple Oracle Document Access (SODA) is a set of NoSQL-style APIs. Documents can be inserted, queried, and retrieved from Oracle Database. By default, documents are JSON strings. SODA APIs exist in many languages. Documentation link for further reading: Simple Oracle Document Access (SODA).

Summary

In this tutorial, you have learned how to:

For further reading see the cx_Oracle documentation.

Appendix: Python Primer

Python is a dynamically typed scripting language. It is most often used to run command-line scripts but is also used for web applications and web services.

Running Python

You can either:

When you run scripts, Python automatically creates bytecode versions of them in a folder called __pycache__. These improve performance of scripts that are run multiple times. They are automatically recreated if the source file changes.

Indentation

Whitespace indentation is significant in Python. When copying examples, use the same column alignment as shown. The samples in this lab use spaces, not tabs.

The following indentation prints 'done' once after the loop has completed:

for i in range(5):
    print(i)
print('done')

But this indentation prints 'done' in each iteration:

for i in range(5):
    print(i)
    print('done')

Strings

Python strings can be enclosed in single or double quotes:

'A string constant'
"another constant"

Multi line strings use a triple-quote syntax:

"""
SELECT *
FROM EMP
"""

Variables

Variables do not need types declared:

count = 1
ename = 'Arnie'

Comments

Comments are either single line:

# a short comment

They can be multi-line using the triple-quote token to create a string that does nothing:

"""
a longer
comment
"""

Printing

Strings and variables can be displayed with a print() function:

print('Hello, World!')
print('Value:', count)

Data Structures

Associative arrays are called 'dictionaries':

a2 = {'PI':3.1415, 'E':2.7182}

Ordered arrays are called 'lists':

a3 = [101, 4, 67]

Lists can be accessed via indexes.

print(a3[0])
print(a3[-1])
print(a3[1:3])

Tuples are like lists but cannot be changed once they are created. They are created with parentheses:

a4 = (3, 7, 10)

Individual values in a tuple can be assigned to variables like:

v1, v2, v3 = a4

Now the variable v1 contains 3, the variable v2 contains 7 and the variable v3 contains 10.

The value in a single entry tuple like "(13,)"can be assigned to a variable by putting a comma after the variable name like:

v1, = (13,)

If the assignment is:

v1 = (13,)

then v1 will contain the whole tuple "(13,)"

Objects

Everything in Python is an object. As an example, given the of the list a3 above, the append() method can be used to add a value to the list.

a3.append(23)

Now a3 contains [101, 4, 67, 23]

Flow Control

Code flow can be controlled with tests and loops. The if/elif/else statements look like:

if v == 2 or v == 4:
    print('Even')
elif v == 1 or v == 3:
    print('Odd')
else:
    print('Unknown number')

This also shows how the clauses are delimited with colons, and each sub block of code is indented.

Loops

A traditional loop is:

for i in range(10):
    print(i)

This prints the numbers from 0 to 9. The value of i is incremented in each iteration.

The 'for' command can also be used to iterate over lists and tuples:

a5 = ['Aa', 'Bb', 'Cc']
for v in a5:
    print(v)

This sets v to each element of the list a5 in turn.

Functions

A function may be defined as:

def myfunc(p1, p2):
    "Function documentation: add two numbers"
    print(p1, p2)
    return p1 + p2

Functions may or may not return values. This function could be called using:

v3 = myfunc(1, 3)

Function calls must appear after their function definition.

Functions are also objects and have attributes. The inbuilt __doc__ attribute can be used to find the function description:

print(myfunc.__doc__)

Modules

Sub-files can be included in Python scripts with an import statement.

import os
import sys

Many predefined modules exist, such as the os and the sys modules.

Resources

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