3. Initializing python-oracledb

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. Both modes have comprehensive functionality supporting the Python Database API v2.0 Specification.

All connections in an application use the same mode. See Finding the python-oracledb Mode to verify which mode is in use.

If you are upgrading a cx_Oracle application to python-oracledb, then refer to Upgrading from cx_Oracle 8.3 to python-oracledb for changes that may be needed.

3.1. Enabling python-oracledb Thick mode

To change from the default Thin mode to the Thick mode:

1. Oracle Client libraries must be available to handle communication to your database. These need to be installed separately, see Installing python-oracledb.

   Oracle Client libraries from one of the following can be used:

• An Oracle Instant Client Basic or Basic Light package. This is generally the easiest if you do not already have Oracle software installed.

• A full Oracle Client installation (installed by running the Oracle Universal installer runInstaller)

• An Oracle Database installation, if Python is running on the same machine as the database

The Client library version does not always have to match the Oracle Database version.

2. Your application must call the function oracledb.init_oracle_client() to load the client libraries. For example, if the Oracle Instant Client libraries are in C:\oracle\instantclient_23_5 on Windows or $HOME/Downloads/instantclient_23_3 on macOS, then you can use:

   import os
   import platform
   
   import oracledb
   
   d = None                               # On Linux, no directory should be passed
   if platform.system() == "Darwin":      # macOS
     d = os.environ.get("HOME")+("/Downloads/instantclient_23_3")
   elif platform.system() == "Windows":   # Windows
     d = r"C:\oracle\instantclient_23_5"
   oracledb.init_oracle_client(lib_dir=d)
   

The use of a ‘raw’ string r"..." on Windows means that backslashes are treated as directory separators. On Linux, the libraries must be in the system library search path before the Python process starts, preferably configured with ldconfig.

More details and options are shown in the later sections:

• Enabling python-oracledb Thick Mode on Windows

• Enabling python-oracledb Thick Mode on macOS

• Enabling python-oracledb Thick Mode on Linux and Related Platforms

Notes on calling init_oracle_client()

• The init_oracle_client() function must be called before any standalone connection or connection pool is created. If a connection or pool is first created, then the Thick mode cannot be enabled.

• If you call init_oracle_client() with a lib_dir parameter, the Oracle Client libraries are loaded immediately from that directory. If you call init_oracle_client() but do not set the lib_dir parameter, the Oracle Client libraries are loaded immediately using the search heuristics discussed in later sections. Note if you set lib_dir on Linux and related platforms, you must still have configured the system library search path to include that directory before starting Python.

• Once the Thick mode is enabled, you cannot go back to the Thin mode except by removing calls to init_oracle_client() and restarting the application.

• If Oracle Client libraries cannot be loaded then init_oracle_client() will raise an error DPI-1047: Oracle Client library cannot be loaded. To resolve this, review the platform-specific instructions below or see Error Messages. Alternatively, remove the call to init_oracle_client() and use Thin mode. The features supported by Thin mode can be found in Appendix B: Differences between python-oracledb Thin and Thick Modes.

• On any operating system, if you set lib_dir to the library directory of a full database or full client installation (such as from running runInstaller), you will need to have previously set the Oracle environment, for example by setting the ORACLE_HOME environment variable. Otherwise you will get errors like ORA-1804. You should set this variable, and other Oracle environment variables, before starting Python, as shown in Oracle Environment Variables.

• The init_oracle_client() function may be called multiple times in your application but must always pass the same arguments.

3.1.1. Enabling python-oracledb Thick Mode on Windows

On Windows, the alternative ways to enable Thick mode are:

• By passing the lib_dir parameter in a call to init_oracle_client(), for example:

  import oracledb
  
  oracledb.init_oracle_client(lib_dir=r"C:\instantclient_23_5")
  

  On Windows, when the path contains backslashes, use a ‘raw’ string like r"C:\instantclient_23_5".

  This directory should contain the libraries from an unzipped Instant Client ‘Basic’ or ‘Basic Light’ package. If you pass the library directory from a full client or database installation, such as Oracle Database “XE” Express Edition, then you will need to have previously set your environment to use that same software installation. Otherwise, files such as message files will not be located and you may have library version clashes.

  If the Oracle Client libraries cannot be loaded, then an exception is raised.

• Alternatively, you can call init_oracle_client() without passing a lib_dir parameter:

  import oracledb
  
  oracledb.init_oracle_client()
  

  In this case, Oracle Client libraries are first looked for in the directory where the python-oracledb binary module is installed. This directory should contain the libraries from an unzipped Instant Client ‘Basic’ or ‘Basic Light’ package.

  If the libraries are not found there, the search looks at the directories on the system library search path, for example, the PATH environment variable.

  If the Oracle Client libraries cannot be loaded, then an exception is raised.

3.1.2. Enabling python-oracledb Thick Mode on macOS

On macOS, the alternative ways to enable Thick mode are:

• By passing the lib_dir parameter in a call to init_oracle_client(), for example:

  import oracledb
  
  oracledb.init_oracle_client(lib_dir="/Users/your_username/Downloads/instantclient_23_3")
  

  This directory should contain the libraries from an unzipped Instant Client ‘Basic’ or ‘Basic Light’ package.

• Alternatively, you can call init_oracle_client() without passing a lib_dir parameter:

  import oracledb
  
  oracledb.init_oracle_client()
  

  In this case, the Oracle Client libraries are first looked for in the directory where the python-oracledb Thick mode binary module is installed. This directory should contain the libraries from an unzipped Instant Client ‘Basic’ or ‘Basic Light’ package, or a symbolic link to the main Oracle Client library if Instant Client is in a different directory.

  You can find the directory containing the Thick mode binary module by calling the python CLI without specifying a Python script, executing import oracledb, and then typing oracledb at the prompt. For example this might show /Users/yourname/.pyenv/versions/3.9.6/lib/python3.9/site-packages/oracledb/__init__.py. After checking that /Users/yourname/.pyenv/versions/3.9.6/lib/python3.9/site-packages/oracledb contains the binary module thick_impl.cpython-39-darwin.so you could then run these commands in a terminal window:

  CLIENT_DIR=~/Downloads/instantclient_23_3
  DPY_DIR=~/.pyenv/versions/3.9.6/lib/python3.9/site-packages/oracledb
  ln -s $CLIENT_DIR/libclntsh.dylib $DPY_DIR
  

  This can be automated in Python with:

  CLIENT_DIR = "~/Downloads/instantclient_23_3"
  LIB_NAME = "libclntsh.dylib"
  
  import os
  import oracledb
  
  target_dir = oracledb.__path__[0]
  os.symlink(os.path.join(CLIENT_DIR, LIB_NAME),
             os.path.join(target_dir, LIB_NAME))
  

  If python-oracledb does not find the Oracle Client library in that directory, the directories on the system library search path may be used, for example, ~/lib/ and /usr/local/lib, or in $DYLD_LIBRARY_PATH. These paths will vary with macOS version and Python version. Any value in DYLD_LIBRARY_PATH will not propagate to a sub-shell, so do not rely on setting it.

  If the Oracle Client libraries cannot be loaded, then an exception is raised.

Ensure that the Python process has directory and file access permissions for the Oracle Client libraries.

3.1.3. Enabling python-oracledb Thick Mode on Linux and Related Platforms

On Linux and related platforms, enable Thick mode by calling init_oracle_client() without passing a lib_dir parameter.

import oracledb

oracledb.init_oracle_client()

Oracle Client libraries are looked for in the operating system library search path, such as configured with ldconfig or set in the environment variable LD_LIBRARY_PATH. This must be configured prior to running the Python process. Web servers and other daemons commonly reset environment variables so using ldconfig is generally preferred instead. On some UNIX platforms an OS specific equivalent, such as LIBPATH or SHLIB_PATH, is used instead of LD_LIBRARY_PATH.

If libraries are not found in the system library search path, then libraries in $ORACLE_HOME/lib will be used. Note that the environment variable ORACLE_HOME should only ever be set when you have a full database installation or full client installation (such as installed with the Oracle GUI installer). It should not be set if you are using Oracle Instant Client. If being used, ORACLE_HOME and other necessary Oracle environment variables should be set before starting Python. See Oracle Environment Variables for python-oracledb Thick Mode.

If the Oracle Client libraries cannot be loaded, then an exception is raised.

On Linux, python-oracledb Thick mode will not automatically load Oracle Client library files from the directory where the python-oracledb binary module is located. One of the above methods should be used instead.

Ensure that the Python process has directory and file access permissions for the Oracle Client libraries. OS restrictions may prevent the opening of Oracle Client libraries installed in unsafe paths, such as from a user directory. You may need to install the Oracle Client libraries under a directory like /opt or /usr/local.

3.1.4. Tracing Oracle Client Libraries Loading

To trace the loading of Oracle Client libraries, the environment variable DPI_DEBUG_LEVEL can be set to 64 before starting Python. At a Windows command prompt, this could be done with:

set DPI_DEBUG_LEVEL=64

On Linux and macOS, you might use:

export DPI_DEBUG_LEVEL=64

When your python-oracledb application is run, logging output is shown on the terminal.

3.2. Explicitly Enabling python-oracledb Thin Mode

Python-oracledb defaults to Thin mode after determining that Thick mode is not going to be used. In one special case, you may wish to explicitly enable Thin mode to prevent Thick mode from being enabled later.

To allow application portability, the driver’s internal logic allows applications to initally attempt standalone connection creation in Thin mode, but then lets them enable Thick mode if that connection is unsuccessful. An example is when trying to connect to an Oracle Database that turns out to be an old version that requires Thick mode. This heuristic means Thin mode is not enforced until the initial connection is successful. Since all connections must be the same mode, any second and subsequent concurrent Thin mode connection attempt will wait for the initial standalone connection to succeed, meaning the driver mode is no longer potentially changeable to Thick mode.

If you have multiple threads concurrently creating standalone Thin mode connections, you may wish to call oracledb.enable_thin_mode() as part of your application initialization. This is not required but avoids the mode determination delay.

The mode determination delay does not affect the following cases, so calling enable_thin_mode() is not needed for them:

• Single-threaded applications using standalone connections.

• Single or multi-threaded applications using connection pools (even with min of 0).

The delay also does not affect applications that have already called oracledb.init_oracle_client() to enable Thick mode.

To explicitly enable Thin mode, call enable_thin_mode(), for example:

import oracledb

oracledb.enable_thin_mode()

Once this method is called, then python-oracledb Thick mode cannot be enabled. If you call oracledb.init_oracle_client(), you will get the following error:

DPY-2019: python-oracledb thick mode cannot be used because thin mode has
already been enabled or a thin mode connection has already been created

If you have already enabled Thick mode by calling oracledb.init_oracle_client() and then call oracledb.enable_thin_mode(), you will get the following error:

DPY-2053: python-oracledb thin mode cannot be used because thick mode has
already been enabled

3.3. Optional Oracle Configuration Files

3.3.1. Optional Oracle Net Configuration Files

Optional Oracle Net configuration files may be read by python-oracledb. These files affect connections and applications. The common files are:

• tnsnames.ora: A configuration file that defines databases addresses for establishing connections. See Net Service Name for Connection Strings.

• sqlnet.ora: A profile configuration file that may contain information on features such as connection failover, network encryption, logging, and tracing. The files should be in a directory accessible to Python, not on the database server host. See Oracle Net Services Reference for more information.

  The sqlnet.ora file is only used in the python-oracledb Thick mode. See Enabling python-oracledb Thick mode. In the python-oracledb Thin mode, many of the equivalent settings can be defined as connection time parameters, for example by using the ConnectParams Class.

See Using Optional Oracle Configuration Files to understand how python-oracledb locates the files.

3.3.2. Optional Oracle Client Configuration File

When python-oracledb Thick mode uses Oracle Client libraries version 12.1 or later, an optional client parameter file called oraaccess.xml can be used to configure some behaviors of those libraries, such as statement caching and prefetching. This can be useful if the application cannot be altered. The file is read from the same directory as the Optional Oracle Net Configuration Files.

Note

The oraaccess.xml file is only used in the python-oracledb Thick mode. See Enabling python-oracledb Thick mode.

A sample oraaccess.xml file that sets the Oracle client ‘prefetch’ value to 1000 rows. This value affects every SQL query in the application:

<?xml version="1.0"?>
 <oraaccess xmlns="http://xmlns.oracle.com/oci/oraaccess"
  xmlns:oci="http://xmlns.oracle.com/oci/oraaccess"
  schemaLocation="http://xmlns.oracle.com/oci/oraaccess
  http://xmlns.oracle.com/oci/oraaccess.xsd">
  <default_parameters>
    <prefetch>
      <rows>1000</rows>
    </prefetch>
  </default_parameters>
</oraaccess>

See Tuning Fetch Performance for information about prefetching.

The oraaccess.xml file has other uses including:

• Changing the value of Fast Application Notification FAN events which affects notifications and Runtime Load Balancing (RLB).

• Configuring Client Result Caching parameters.

• Turning on Client Statement Cache Auto-tuning.

Refer to the documentation on oraaccess.xml for more details.

See Using Optional Oracle Configuration Files to understand how python-oracledb locates the files.

3.3.3. Using Optional Oracle Configuration Files

If you use optional Oracle configuration files such as tnsnames.ora, sqlnet.ora or oraaccess.xml, then put the files in an accessible directory and follow the Thin or Thick mode instructions below.

The files should be in a directory accessible to Python, not on the database server host.

For python-oracledb Thin mode

In python-oracledb Thin mode, you must specify the directory that contains the tnsnames.ora file by either:

• Setting the TNS_ADMIN environment variable to the directory containing the file.

• Or setting defaults.config_dir to the directory containing the file. For example:

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

• Or setting the config_dir parameter to the directory containing the file when connecting or creating a connection pool. For example:

  connection = oracledb.connect(user="hr", password=userpwd, dsn="orclpdb",
                            config_dir="/opt/oracle/config")
  

On Windows, when the path contains backslashes, use a ‘raw’ string like r"C:\instantclient_23_5".

Note

In Thin mode, you must explicitly set the directory because traditional “default” locations such as the Instant Client network/admin/ subdirectory, or $ORACLE_HOME/network/admin/, or $ORACLE_BASE/homes/XYZ/network/admin/ (in a read-only Oracle Database home) are not automatically looked in.

For python-oracledb Thick mode

In python-oracledb Thick mode, the directory containing the optional files can be explicitly specified or a default location will be used. Do one of:

• Set the config_dir parameter to the directory containing the files in the oracledb.init_oracle_client() call:

  oracledb.init_oracle_client(config_dir="/opt/oracle/config")
  

  On Windows, when the path contains backslashes, use a ‘raw’ string like r"C:\instantclient_23_5".

Note

In python-oracledb Thick mode, once an application has created its first connection, trying to change the configuration directory will not have any effect.

• If init_oracle_client() is called to enable Thick mode but config_dir is not specified, then default directories are searched for the configuration files. They include:

  • The directory specified by the TNS_ADMIN environment variable.

  • For Oracle Instant Client ZIP files, the network/admin subdirectory of Instant Client, for example /opt/oracle/instantclient_23_5/network/admin.

  • For Oracle Instant Client RPMs, the network/admin subdirectory of Instant Client, for example /usr/lib/oracle/23.5/client64/lib/network/admin.

  • When using libraries from a local Oracle Database or full client installation, in $ORACLE_HOME/network/admin or $ORACLE_BASE_HOME/network/admin.

Note that the Easy Connect Syntax for Connection Strings can set many common configuration options without needing tnsnames.ora or sqlnet.ora files.

The section Network Configuration has additional information about Oracle Net configuration.

3.4. Oracle Environment Variables for python-oracledb Thick Mode

Some common environment variables that influence python-oracledb are shown below. The variables that may be needed depend on how Python is installed, how you connect to the database, and what optional settings are desired. It is recommended to set Oracle variables in the environment before calling Python. However, they may also be set in the application with os.putenv() before the first connection is established. System environment variables like LD_LIBRARY_PATH must be set before Python starts.

Note

The variables listed below are only supported in the python-oracledb Thick mode, with the exception of TNS_ADMIN and ORA_SDTZ which are also supported in the python-oracledb Thin mode.

Table 3.1 Common Oracle environment variables

Oracle Environment Variables	Purpose
LD_LIBRARY_PATH	The library search path for platforms like Linux should include the Oracle libraries, for example $ORACLE_HOME/lib or /opt/instantclient_23_5. This variable is not needed if the libraries are located by an alternative method, such as with ldconfig. On other UNIX platforms, you may need to set an OS specific equivalent such as LIBPATH or SHLIB_PATH.
PATH	The library search path for Windows should include the location where OCI.DLL is found. Not needed if you set lib_dir in a call to oracledb.init_oracle_client()
TNS_ADMIN	The directory of optional Oracle Client configuration files such as tnsnames.ora and sqlnet.ora. Not needed if the configuration files are in a default location or if config_dir was not used in oracledb.init_oracle_client(). See Optional Oracle Net Configuration Files.
ORA_SDTZ	The default session time zone.
ORA_TZFILE	The name of the Oracle time zone file to use. See Time Zone Files.
ORACLE_HOME	The directory containing the Oracle Database software. The directory and various configuration files must be readable by the Python process. This variable should not be set if you are using Oracle Instant Client.
NLS_LANG	Determines the ‘national language support’ globalization options for python-oracledb. Note that from cx_Oracle 8, the character set component is ignored and only the language and territory components of NLS_LANG are used. The character set can instead be specified during connection or connection pool creation. See Character Sets and Globalization.
NLS_DATE_FORMAT, NLS_TIMESTAMP_FORMAT	Often set in Python applications to force a consistent date format independent of the locale. The variables are ignored if the environment variable NLS_LANG is not set.

3.5. Other python-oracledb Thick Mode Initialization

The oracledb.init_oracle_client() function allows driver_name and error_url parameters to be set. These are useful for applications whose end-users are not aware that python-oracledb is being used. An example of setting the parameters is:

oracledb.init_oracle_client(driver_name="My Great App : 3.1.4",
                            error_url="https://example.com/MyInstallInstructions.html")

The convention for driver_name is to separate the product name from the product version by a colon and single blank characters. The value will be shown in Oracle Database views like V$SESSION_CONNECT_INFO. If this parameter is not specified, then the value specified in the oracledb.defaults.driver_name attribute is used. If the value of this attribute is None, then a value like python-oracledb thk : 1.2.0 is shown, see Finding the python-oracledb Mode.

The error_url string will be shown in the exception raised if init_oracle_client() cannot load the Oracle Client libraries. This allows applications that use python-oracledb in Thick mode to refer users to application-specific installation instructions. If this value is not specified, then the Installing python-oracledb URL is used.

3.6. Migrating from python-oracledb Thick Mode to python-oracledb Thin Mode

Changing an application that currently uses Thick mode to use Thin mode requires the removal of calls to oracledb.init_oracle_client() and an application restart. Other small changes may be required.

All connections in a python-oracledb application must use the same mode.

If you have been using python-oracledb in Thick mode, you can use Thin mode by:

1. Reviewing Appendix A: Oracle Database Features Supported by python-oracledb and Appendix B: Differences between python-oracledb Thin and Thick Modes for code changes that may be needed. Also read Toggling between Drivers.

2. Removing all calls to oracledb.init_oracle_client() from the application.

3. Make other necessary changes identified in step 1.

4. When you are satisfied, you can optionally remove Oracle Client libraries. For example, delete your Oracle Instant Client directory.

You can validate the python-oracledb mode by querying the CLIENT_DRIVER column of V$SESSION_CONNECT_INFO and verifying if the value of the column begins with the text python-oracledb thn. See Finding the python-oracledb Mode.