Characters Sets and National Language Support (NLS)¶
Data fetched from, and sent to, Oracle Database will be mapped between the database character set and the “Oracle client” character set of the Oracle client libraries used by cx_Oracle. If data cannot be correctly mapped between client and server character sets, then it may be corrupted or queries may fail with “codec can’t decode byte”. Most applications will need to specify the client character set.
cx_Oracle uses Oracle’s National Language Support (NLS) to assist in globalizing applications. As well as character set support, there are many other features that will be useful in applications. See the Database Globalization Support Guide.
Setting the Client Character Set¶
import cx_Oracle connection = cx_Oracle.connect(connectString, encoding="UTF-8", nencoding="UTF-8")
encoding parameter affects character data such as VARCHAR2 and CLOB
nencoding parameter affects “National Character” data such as
NVARCHAR2 and NCLOB. If you are not using national character types, then you
cx_Oracle will first treat the encoding parameter values as IANA encoding names. If
no name is matched, it will attempt to use Oracle character set names. For
UTF-8 characters you should use the IANA name “UTF-8” or the
Oracle name “AL32UTF8”. Do not accidentally use “UTF8”, which Oracle uses to
specify the older Unicode 3.0 Universal character set,
An alternative to setting the encoding parameters is to set Oracle’s
NLS_LANG environment variable to a value such as
AMERICAN_AMERICA.AL32UTF8. See Setting environment variables. As well as setting the character set, the
variable lets you specify the Language (
AMERICAN in this example) and
AMERICA) used for NLS globalization. See Choosing a Locale with
the NLS_LANG Environment Variable.
A character set specified by an
encoding parameter will override the
character set in
NLS_LANG. The language and territory components will still
be used by Oracle.
NLS_LANG environment variable is set in the application with
os.environ['NLS_LANG'], it must be set before any connection pool is created,
or before any standalone connections are created.
Other Oracle globalization variable can also be set, see Setting NLS Parameters.
Character Set Example¶
The script below tries to display data containing a Euro symbol from the
NLS_LANG environment variable on the operating system is set
connection = cx_Oracle.connect(userName, password, "dbhost.example.com/orclpdb1") cursor = connection.cursor() for row in cursor.execute("select * from nchar_test"): print(row) print(connection.encoding) print(connection.nencoding)
Because the ‘€’ symbol is not supported by the
WE8ISO8859P1 character set,
all ‘€’ characters are replaced by ‘¿’ in the cx_Oracle output:
('¿', 'test ', 'test', 'test ') ('¿', 'test ', '¿', 'test ') ('"nvarchar"', '/"nchar" ', 'varchardata', 'chardata ') ('°', 'Second ', 'Third', 'Fourth ') ISO-8859-1 ISO-8859-1
encoding parameter is set during connection:
connection = cx_Oracle.connect(userName, password, "dbhost.example.com/orclpdb1", encoding="UTF-8", nencoding="UTF-8")
Then the output displays the Euro symbol as desired:
('€', 'test ', 'test', 'test ') ('€', 'test ', '€', 'test ') ('"nvarchar"', '/"nchar" ', 'varchardata', 'chardata ') ('°', 'Second ', 'Third', 'Fourth ') UTF-8 UTF-8
Finding the Database and Client Character Set¶
To find the database character set, execute the query:
SELECT value AS db_charset FROM nls_database_parameters WHERE parameter = 'NLS_CHARACTERSET';
To find the current “client” character set used by cx_Oracle, execute the query:
SELECT DISTINCT client_charset AS client_charset FROM v$session_connect_info WHERE sid = SYS_CONTEXT('USERENV', 'SID');
If these character sets do not match, characters will be mapped when transferred over Oracle Net. This may impact performance and may result in invalid data.