# 25. Appendix C: The python-oracledb and cx_Oracle Drivers

The python-oracledb driver is the renamed, major version successor to cx_Oracle 8.3. As a major release, the python-oracledb driver has new features and some Deprecations. Also see Upgrading from cx_Oracle 8.3 to python-oracledb.

## 25.1. Differences between the python-oracledb and cx_Oracle Drivers

The differences between the cx_Oracle 8.3 and python-oracledb drivers are listed here.

### 25.1.1. Mode differences from cx_Oracle

By default, python-oracledb runs in a ‘Thin’ mode which connects directly to Oracle Database. This mode does not need Oracle Client libraries. However, some additional functionality is available when python-oracledb uses them. Python-oracledb is said to be in ‘Thick’ mode when Oracle Client libraries are used. See Enabling python-oracledb Thick mode. Both modes have comprehensive functionality supporting the Python Database API v2.0 Specification.

cx_Oracle always runs in a Thick mode using Oracle Client libraries. The features in python-oracledb Thick mode and cx_Oracle 8.3 are the same, subject to the new features, some deprecations, and to other changes noted in this section.

### 25.1.2. Oracle Client Library Loading Differences from cx_Oracle

Oracle Client libraries are now only loaded if `oracledb.init_oracle_client()` is called in your application. This changes python-oracledb to Thick mode. The `init_oracle_client()` method must be called before any standalone connection or connection pool is created. If a connection or pool is created first in the default Thin mode, then Thick mode cannot be enabled.

See Enabling python-oracledb Thick mode for more information.

Calling the `init_oracle_client()` method immediately loads Oracle Client libraries. To emulate the cx_Oracle behavior of deferring library loading until the creation of the first connection (in the case when `init_oracle_client()` is not called), your application will need to defer calling `init_oracle_client()` as appropriate.

In python-oracledb, `init_oracle_client()` can now be called multiple times in the one Python process as long as its arguments are the same each time.

#### 25.1.2.1. oracledb.clientversion()

The `oracledb.clientversion()` method shows the version of the Oracle Client libraries being used. There is no Oracle Client used in the python-oracledb Thin mode so this function can only be called in python-oracledb Thick mode. If this function is called before `oracledb.init_oracle_client()`, an exception is thrown.

### 25.1.3. Connection Differences from cx_Oracle

#### 25.1.3.1. oracledb.connect() Differences

The `oracledb.connect()` function in the python-oracledb driver differs from cx_Oracle:

- Keyword parameters must be used in calls to `oracledb.connect()`. This change makes the driver compliant with the Python Database API specification PEP 249. See Standalone Connections and Common Connection Errors.

- New keyword arguments can be passed to `connect()`. For example you can pass the hostname, port and servicename as separate parameters instead of using an Easy Connect connection string. In python-oracledb Thin mode, some of the new arguments replace `sqlnet.ora` settings.

- A new optional parameter `params` of type ConnectParams can be used to encapsulate connection properties. See Using the ConnectParams Builder Class for more information.

- The following parameters are deprecated and ignored:

  - `encoding` and `nencoding`: The encodings in use are always UTF-8.

  - `threaded`: Threaded Oracle Call Interface (OCI) is now always enabled in Thick mode. This option is not relevant to the Thin mode.

  See Deprecations for more information.

The use of the class constructor method `oracledb.Connection()` to create connections is no longer recommended for creating connections. Use `connect()` instead.

#### 25.1.3.2. Connection Object Differences

The Connection object differences between the python-oracledb and cx_Oracle drivers are:

- The attribute `Connection.maxBytesPerCharacter` is deprecated. This will return a constant value of 4 since encodings are always UTF-8.

- A new boolean attribute, `Connection.thin` is available. This attribute is True if the connection was established in the Thin mode. In Thick mode, the value of this attribute is False.

See Connection Attributes for more information.

### 25.1.4. Pooling Differences from cx_Oracle

It is recommended to use the new equivalent ConnectionPool Object instead of the SessionPool object, which is deprecated. To create a connection pool, use `oracledb.create_pool()`, which is equivalent to calling cx_Oracle.SessionPool().

For more information, see Connection Pooling.

#### 25.1.4.1. oracledb.SessionPool() Differences

The python-oracledb `oracledb.SessionPool()` method (which is an alias of `oracledb.create_pool()`) differs from cx_Oracle.SessionPool() as follows:

- Keyword parameters must be used in calls. This change makes the driver compliant with the Python Database API specification PEP 249. See Connection pooling and Common Connection Errors.

- Passing a value to the `dsn` parameter that contains the user name and password is now supported in the same way as `oracledb.connect()`. For example `dsn="un/pw@cs"` can be used.

- New keyword arguments can be passed to `create_pool()`. For example you can pass the hostname, port and servicename as separate parameters instead of using an Easy Connect connection string. In python-oracledb Thin mode, some of the new arguments replace `sqlnet.ora` settings.

- The default mode is `POOL_GETMODE_WAIT` instead of `POOL_GETMODE_NOWAIT`. If the mode `POOL_GETMODE_NOWAIT` is truly desired, modify any pool creation code to specify this value instead. Note the namespace of constant has been improved. Old names like `SPOOL_ATTRVAL_NOWAIT` can be used but are now deprecated.

- A new optional parameter `params` of type PoolParams can be used to encapsulate connection properties. See Using the ConnectParams Builder Class for more information.

- The `encoding` and `decoding` parameters are deprecated and ignored. The encodings in use are always UTF-8.

- New keyword arguments that are used internally to create a PoolParams object before creating the connection.

#### 25.1.4.2. SessionPool Object Differences

The SessionPool object (which is an alias for the ConnectionPool object) differences between the python-oracledb and cx_Oracle drivers are:

- A Python type() will show the class as `oracledb.ConnectionPool` instead of `cx_Oracle.SessionPool`.

- A new boolean attribute, `SessionPool.thin` (see `ConnectionPool.thin`) is available. This attribute is True if the connection was established in the Thin mode. In Thick mode, the value of this attribute is False.

### 25.1.5. Cursor Object Differences from cx_Oracle

The differences between the Cursor object in python-oracledb and cx_Oracle drivers are:

- `Cursor.fetchmany()`: The name of the size argument of `fetchmany()` is `size`. This change was done to comply with PEP 249. The previous keyword argument name, `numRows` is deprecated.

- `Cursor.fetchraw()`: This method was previously deprecated in cx_Oracle 8.2 and has been removed in python-oracledb. Instead, use one of the other fetch methods such as `Cursor.fetchmany()`.

- `Cursor.executemanyprepared()`: This method was previously deprecated in cx_Oracle 6.4 and has been removed in python-oracledb. Instead, use `Cursor.executemany()`, by passing None for the statement argument and an integer for the parameters argument.

- `Cursor.bindarraysize`: This attribute is deprecated and removed in python-oracledb. It is not needed in the application code.

- `Cursor.rowcount`: After `Cursor.execute()` or `Cursor.executemany()` with PL/SQL statements, `Cursor.rowcount` will return 0. If the cursor or connection are not open, then the value -1 will be returned as required by the Python Database API.

### 25.1.6. Advanced Queuing (AQ) Differences from cx_Oracle

The old Advanced Queuing (AQ) API is not available in python-oracledb since it was deprecated in cx_Oracle 7.2. Use the new Advanced Queuing (AQ). Note that AQ is only available in the Thick mode.

Replace:

- `Connection.deq()` with `Queue.deqone()` or `Queue.deqmany()`

- `Connection.deqoptions()` with attribute `Queue.deqoptions`

- `Connection.enq()` with `Queue.enqone()` or `Queue.enqmany()`

- `Connection.deqoptions()` with attribute `Queue.deqoptions`

The AQ feature in the python-oracledb driver differs from cx_Oracle as follows:

- AQ messages can be enqueued and dequeued as a JSON payload type

- Recipient lists can be enqueued and dequeued

- Enqueue options, dequeue options, and message properties can be set

See Oracle Advanced Queuing (AQ).

### 25.1.7. Error Handling Differences from cx_Oracle

In python-oracledb Thick mode, error messages generated by the Oracle Client libraries and the ODPI-C layer used by cx_Oracle and python-oracledb in Thick mode are mostly returned unchanged from cx_Oracle 8.3 with the exceptions shown below.

Note that the python-oracledb driver error messages can vary between Thin and Thick modes. See Error Handling in Thin and Thick Modes.

#### 25.1.7.1. ConnectionPool.acquire() Message Differences

`ConnectionPool.acquire()` ORA errors will be mapped to DPY errors. For example:

    DPY-4005: timed out waiting for the connection pool to return a connection

replaces the cx_Oracle 8.3 error:

    ORA-24459: OCISessionGet() timed out waiting for pool to create new connections

#### 25.1.7.2. Dead Connection Detection and Timeout Message Differences

Application code which detects connection failures or statement execution timeouts will need to check for new errors, DPY-4011 and DPY-4024 respectively. The error DPY-1001 is returned if an already dead connection is attempted to be used.

The new Error object attribute `full_code` may be useful for checking the error code.

Example error messages are:

- Scenario 1: An already closed or dead connection was attempted to be used.

  python-oracledb Thin Error:

      DPY-1001: not connected to database

  python-oracledb Thick Error:

      DPY-1001: not connected to database

  cx_Oracle Error:

      not connected

- Scenario 2: The database side of the connection was terminated while the connection was being used.

  python-oracledb Thin Error:

      DPY-4011: the database or network closed the connection

  python-oracledb Thick Error:

      DPY-4011: the database or network closed the connection
      DPI-1080: connection was closed by ORA-%d

  cx_Oracle Error:

      DPI-1080: connection was closed by ORA-%d

- Scenario 3: Statement execution exceeded the `connection.call_timeout` value.

  python-oracledb Thin Error:

      DPY-4024: call timeout of {timeout} ms exceeded

  python-oracledb Thick Error:

      DPY-4024: call timeout of {timeout} ms exceeded
      DPI-1067: call timeout of %u ms exceeded with ORA-%d

  cx_Oracle Error:

      DPI-1067: call timeout of %u ms exceeded with ORA-%d

## 25.2. Upgrading from cx_Oracle 8.3 to python-oracledb

This section provides the detailed steps needed to upgrade from cx_Oracle 8.3 to python-oracledb.

### 25.2.1. Things to Know Before the Upgrade

Below is a list of some useful things to know before upgrading from cx_Oracle to python-oracledb:

- You can have both cx_Oracle and python-oracledb installed, and can use both in the same application.

- If you only want to use the python-oracledb driver in Thin mode, then you do not need Oracle Client libraries such as from Oracle Instant Client. You only need to install the driver itself:

      python -m pip install oracledb

  See Appendix B: Differences between python-oracledb Thin and Thick Modes.

- The python-oracledb Thin and Thick modes have the same level of support for the Python Database API specification and can be used to connect to on-premises databases and Oracle Cloud databases. However, the python-oracledb Thin mode does not support some of the advanced Oracle Database features such as Application Continuity (AC), Advanced Queuing (AQ), Continuous Query Notification (CQN), and Sharding. See Features Supported for details.

- python-oracledb can be used in SQLAlchemy, Django, Pandas, and other frameworks and Object-relational Mappers (ORMs). Until they add native support, you can override the use of cx_Oracle with a few lines of code. See Python Frameworks, SQL Generators, and ORMs.

- python-oracledb connection and pool creation calls require keyword arguments to conform with the Python Database API specification. For example you must use:

      oracledb.connect(user="scott", password=pw, dsn="localhost/orclpdb")

  This no longer works:

      oracledb.connect("scott", pw, "localhost/orclpdb")

- The python-oracledb Thin mode ignores all NLS environment variables. It also ignores `ORA_SDTZ` and `ORA_TZFILE` environment variables. Thick mode does use these variables. See Character Sets and Globalization for alternatives.

- To use a `tnsnames.ora` file in the python-oracledb Thin mode, you must explicitly set the environment variable `TNS_ADMIN` to the directory containing the file, or set `defaults.config_dir`, or set the `config_dir` parameter when connecting.

  Only python-oracledb Thick mode will read `sqlnet.ora` files. The Thin mode lets equivalent properties be set in the application when connecting.

  Configuration files in a “default” location such as the Instant Client `network/admin/` subdirectory, in `$ORACLE_HOME/network/admin/`, or in `$ORACLE_BASE/homes/XYZ/network/admin/` (in a read-only Oracle Database home) is not automatically loaded in Thin mode. Default locations are automatically searched by Thick mode.

- To use the python-oracledb Thin mode in an ORACLE_HOME database installation environment, you use an explicit connection string since the `ORACLE_SID`, `TWO_TASK` and `LOCAL` environment variables are not used. They are used in Thick mode.

- This is a major release so some previously deprecated features are no longer available. See Deprecations.

### 25.2.2. Steps to Upgrade to python-oracledb

If you are creating new applications, follow Installing python-oracledb and refer to other sections of the documentation for usage information.

To upgrade existing code from cx_Oracle to python-oracledb, perform the following steps:

1. Install the new python-oracledb module:

       python -m pip install oracledb

   See Installing python-oracledb for more details.

2. Import the new interface module. This can be done in two ways. You can change:

       import cx_Oracle

   to:

       import oracledb as cx_Oracle

   Alternatively, you can replace all references to the module `cx_Oracle` with `oracledb`. For example, change:

       import cx_Oracle
       c = cx_Oracle.connect(...)

   to:

       import oracledb
       c = oracledb.connect(...)

   Any new code being introduced during the upgrade should aim to use the latter syntax.

3. Use keyword parameters in calls to `oracledb.connect()`, `oracledb.Connection()`, and `oracledb.SessionPool()`.

   You must replace positional parameters with keyword parameters, unless only one parameter is being passed. Python-oracledb uses keyword parameters exclusively unless a DSN containing the user, password, and connect string combined, for example `un/pw@cs`, is used. This change makes the driver compliant with the Python Database API specification PEP 249.

   For example, the following code will fail:

       c = oracledb.connect("un", "pw", "cs")

   and needs to be changed to:

       c = oracledb.connect(user="un", password="pw", dsn="cs")

   The following example will continue to work without change:

       c = oracledb.connect("un/pw@cs")

4. Review obsolete encoding parameters in calls to `oracledb.connect()`, `oracledb.Connection()`, and `oracledb.SessionPool()`:

   - `encoding` and `nencoding` are ignored by python-oracledb. The python-oracledb driver uses UTF-8 exclusively.

   - `threaded` is ignored in `oracledb.connect()` and `oracledb.Connection()` by python-oracledb. This parameter was already ignored in `oracledb.SessionPool()` from cx_Oracle 8.2.

5. Remove all references to `Cursor.fetchraw()` as this method was deprecated in cx_Oracle 8.2 and has been removed in python-oracledb. Instead, use one of the other fetch methods such as `Cursor.fetchmany()`.

6. The default value of the `oracledb.SessionPool()` parameter `getmode` now waits for an available connection. That is the default is now `SPOOL_ATTRVAL_WAIT` instead of `SPOOL_ATTRVAL_NOWAIT`. The new default value improves the behavior for most applications. If the pool is in the middle of growing, the new value prevents transient connection creation errors from occurring when using the Thin mode, or when using the Thick mode with recent Oracle Client libraries.

   If the old default value is required, modify any pool creation code to explicitly specify `getmode=oracledb.POOL_SPOOL_ATTRVAL_NOWAIT`.

   Note a ConnectionPool class deprecates the equivalent SessionPool class. The method `oracledb.create_pool()` deprecates the use of `oracledb.SessionPool()`. New pool parameter constant names such as `POOL_GETMODE_NOWAIT` and `PURITY_SELF` are now preferred. The old namespaces still work.

7. Review the following sections to see if your application requirements are satisfied by the python-oracledb Thin mode:

   - Appendix A: Oracle Database Features Supported by python-oracledb

   - Appendix B: Differences between python-oracledb Thin and Thick Modes

   If your application requirements are not supported by the Thin mode, then use the python-oracledb Thick mode.

8. Review Differences between the python-oracledb and cx_Oracle Drivers.

   If your code base uses an older cx_Oracle version, review the previous release notes for additional changes to modernize the code.

9. Modernize code as needed or desired. See Deprecations for the list of deprecations in python-oracledb 1.0.

#### 25.2.2.1. Additional Upgrade Steps to use python-oracledb Thin Mode

To use python-oracledb Thin mode, the following changes need to be made in addition to the common Steps to Upgrade to python-oracledb:

1. Remove calls to `init_oracle_client()` since this turns on the python-oracledb Thick mode.

2. If the `config_dir` parameter of `init_oracle_client()` had been used, then set the new `defaults.config_dir` attribute to the desired value or set the `config_dir` parameter when connecting. For example:

       oracledb.defaults.config_dir = "/opt/oracle/config"

   Also see Oracle Net Services and Client Configuration Files.

3. If the application is connecting using an Oracle Net service name from a `tnsnames.ora` file located in a “default” location such as the Instant Client `network/admin/` subdirectory, in `$ORACLE_HOME/network/admin/`, or in `$ORACLE_BASE/homes/XYZ/network/admin/` (in a read-only Oracle Database home), then the configuration file directory must now explicitly be set as shown above.

4. Remove calls to `oracledb.clientversion()` which is only available in the python-oracledb Thick mode. Oracle Client libraries are not available in Thin mode.

5. Ensure that any assumptions about when connections are created in the connection pool are eliminated. The python-oracledb Thin mode creates connections in a daemon thread and so the attribute `ConnectionPool.opened` will change over time and will not be equal to `ConnectionPool.min` immediately after the pool is created. Note that this behavior is also similar in recent versions of the Oracle Call Interface (OCI) Session Pool used by the Thick mode. Unless the `oracledb.SessionPool()` function’s parameter `getmode` is `SPOOL_ATTRVAL_WAIT` (or the new equivalent `oracledb.POOL_GETMODE_WAIT`), then applications should not call `ConnectionPool.acquire()` until sufficient time has passed for connections in the pool to be created.

6. Review error handling improvements. See Error Handling in Thin and Thick Modes.

7. Review locale and globalization usage. See Character Sets and Globalization.

#### 25.2.2.2. Additional Upgrade Steps to use python-oracledb Thick Mode

To use python-oracledb Thick mode, the following changes need to be made in addition to the common Steps to Upgrade to python-oracledb:

1. The function `init_oracle_client()` must be called. It can be called anywhere before the first call to `connect()`, `oracledb.Connection()`, and `oracledb.SessionPool()`. This enables the Thick mode. See Enabling python-oracledb Thick mode for more details.

   The requirement to call `init_oracle_client()` means that Oracle Client library loading is not automatically deferred until the driver is first used, such as when a connection is opened. The application must explicitly manage this, if deferral is required. In python-oracledb, `init_oracle_client()` can be called multiple times in a Python process as long as arguments are the same.

   Note that on Linux and related operating systems, the `init_oracle_client()` parameter `lib_dir` should not be passed. Instead, set the system library search path with `ldconfig` or `LD_LIBRARY_PATH` prior to running Python.

2. Replace all usages of the deprecated Advanced Queuing API with the new AQ API originally introduced in cx_Oracle 7.2, see the cx_Oracle Advanced Queuing (AQ) documentation.

3. Review error handling improvements. See Error Handling in Thin and Thick Modes.

### 25.2.3. Code to Aid the Upgrade to python-oracledb

#### 25.2.3.1. Toggling between Drivers

The sample oracledb_upgrade.py shows a way to toggle applications between cx_Oracle and the two python-oracledb modes. Note this script cannot map some functionality such as obsolete cx_Oracle features or error message changes.

An example application showing this module in use is:

    # test.py

    import oracledb_upgrade as cx_Oracle
    import os

    un = os.environ.get("PYTHON_USERNAME")
    pw = os.environ.get("PYTHON_PASSWORD")
    cs = os.environ.get("PYTHON_CONNECTSTRING")

    connection = cx_Oracle.connect(user=un, password=pw, dsn=cs)
    with connection.cursor() as cursor:
        sql = """SELECT UNIQUE CLIENT_DRIVER
                 FROM V$SESSION_CONNECT_INFO
                 WHERE SID = SYS_CONTEXT('USERENV', 'SID')"""
        for r, in cursor.execute(sql):
            print(r)

You can then choose what mode is in use by setting the environment variable `ORA_PYTHON_DRIVER_TYPE` to one of “cx”, “thin”, or “thick”:

    export ORA_PYTHON_DRIVER_TYPE=thin
    python test.py

Output shows the python-oracledb Thin mode was used:

    python-oracledb thn : 1.0.0

You can customize `oracledb_upgrade.py` to your needs. For example, if your connection and pool creation calls always use keyword parameters, you can remove the shims that map from positional arguments to keyword arguments.

The simplest form is shown in Python Frameworks, SQL Generators, and ORMs.

#### 25.2.3.2. Testing Which Driver is in Use

To know whether the driver is cx_Oracle or python-oracledb, you can use code similar to:

    import oracledb as cx_Oracle
    # or:
    # import cx_Oracle

    if cx_Oracle.__name__ == 'cx_Oracle':
           print('cx_Oracle')
    else:
           print('oracledb')

Another method that can be used to check which driver is in use is to query `V$SESSION_CONNECT_INFO`, see Finding the Python-oracledb Mode.

### 25.2.4. Python Frameworks, SQL Generators, and ORMs

The python-oracledb Thin mode features in the python-oracledb cover the needs of frameworks that depend upon the Python Database API.

Until SQLAlchemy, Django, other frameworks, object-relational mappers (ORMs), and libraries add native support for python-oracledb, you can add temporary code like this to use python-oracledb in-place of cx_Oracle:

    import sys
    import oracledb
    oracledb.version = "8.3.0"
    sys.modules["cx_Oracle"] = oracledb
    import cx_Oracle

Note

The import of cx_Oracle occurs last. This code must be run before the library code does its own import of cx_Oracle.