psycopg2.errors - Exception classes mapping PostgreSQL errors - Psycopg 2.8.6 documentation

psycopg2.errors - Exception classes mapping PostgreSQL errors

This module exposes the classes psycopg raises upon receiving an error from the database with a SQLSTATE value attached (available in the pgcode attribute). The content of the module is generated from the PostgreSQL source code and includes classes for every error defined by PostgreSQL in versions between 9.1 and 13.

Every class in the module is named after what referred as "condition name" in the documentation , converted to CamelCase: e.g. the error 22012, division_by_zero is exposed by this module as the class DivisionByZero .

Every exception class is a subclass of one of the standard DB-API exception and expose the Error interface. Each class’ superclass is what used to be raised by psycopg in versions before the introduction of this module, so everything should be compatible with previously written code catching one the DB-API class: if your code used to catch IntegrityError to detect a duplicate entry, it will keep on working even if a more specialised subclass such as UniqueViolation is raised.

The new classes allow a more idiomatic way to check and process a specific error among the many the database may return. For instance, in order to check that a table is locked, the following code could have been used previously:

try:
    cur.execute("LOCK TABLE mytable IN ACCESS EXCLUSIVE MODE NOWAIT")
except psycopg2.OperationalError as e:
    if e.pgcode == psycopg2.errorcodes.LOCK_NOT_AVAILABLE:
        locked = True
    else:
        raise

While this method is still available, the specialised class allows for a more idiomatic error handler:

try:
    cur.execute("LOCK TABLE mytable IN ACCESS EXCLUSIVE MODE NOWAIT")
except psycopg2.errors.LockNotAvailable:
    locked = True

psycopg2.errors. lookup ( code )

Lookup an error code and return its exception class.

Raise KeyError if the code is not found.

try:
    cur.execute("LOCK TABLE mytable IN ACCESS EXCLUSIVE MODE NOWAIT")
except psycopg2.errors.lookup("55P03"):
    locked = True