Current File : //opt/alt/python37/share/doc/alt-python37-psycopg2-2.8.4/doc/src/module.rst
The `psycopg2` module content
==================================
.. sectionauthor:: Daniele Varrazzo <daniele.varrazzo@gmail.com>
.. module:: psycopg2
The module interface respects the standard defined in the |DBAPI|_.
.. index::
single: Connection string
double: Connection; Parameters
single: Username; Connection
single: Password; Connection
single: Host; Connection
single: Port; Connection
single: DSN (Database Source Name)
.. function::
connect(dsn=None, connection_factory=None, cursor_factory=None, async=False, \*\*kwargs)
Create a new database session and return a new `connection` object.
The connection parameters can be specified as a `libpq connection
string`__ using the *dsn* parameter::
conn = psycopg2.connect("dbname=test user=postgres password=secret")
or using a set of keyword arguments::
conn = psycopg2.connect(dbname="test", user="postgres", password="secret")
or using a mix of both: if the same parameter name is specified in both
sources, the *kwargs* value will have precedence over the *dsn* value.
Note that either the *dsn* or at least one connection-related keyword
argument is required.
The basic connection parameters are:
- `!dbname` -- the database name (`!database` is a deprecated alias)
- `!user` -- user name used to authenticate
- `!password` -- password used to authenticate
- `!host` -- database host address (defaults to UNIX socket if not provided)
- `!port` -- connection port number (defaults to 5432 if not provided)
Any other connection parameter supported by the client library/server can
be passed either in the connection string or as a keyword. The PostgreSQL
documentation contains the complete list of the `supported parameters`__.
Also note that the same parameters can be passed to the client library
using `environment variables`__.
.. __:
.. _connstring: https://www.postgresql.org/docs/current/static/libpq-connect.html#LIBPQ-CONNSTRING
.. __:
.. _connparams: https://www.postgresql.org/docs/current/static/libpq-connect.html#LIBPQ-PARAMKEYWORDS
.. __:
.. _connenvvars: https://www.postgresql.org/docs/current/static/libpq-envars.html
Using the *connection_factory* parameter a different class or
connections factory can be specified. It should be a callable object
taking a *dsn* string argument. See :ref:`subclassing-connection` for
details. If a *cursor_factory* is specified, the connection's
`~connection.cursor_factory` is set to it. If you only need customized
cursors you can use this parameter instead of subclassing a connection.
Using *async*\=\ `!True` an asynchronous connection will be created: see
:ref:`async-support` to know about advantages and limitations. *async_* is
a valid alias for the Python version where ``async`` is a keyword.
.. versionchanged:: 2.4.3
any keyword argument is passed to the connection. Previously only the
basic parameters (plus `!sslmode`) were supported as keywords.
.. versionchanged:: 2.5
added the *cursor_factory* parameter.
.. versionchanged:: 2.7
both *dsn* and keyword arguments can be specified.
.. versionchanged:: 2.7
added *async_* alias.
.. seealso::
- `~psycopg2.extensions.parse_dsn`
- libpq `connection string syntax`__
- libpq supported `connection parameters`__
- libpq supported `environment variables`__
.. __: connstring_
.. __: connparams_
.. __: connenvvars_
.. extension::
The non-connection-related keyword parameters are Psycopg extensions
to the |DBAPI|_.
.. data:: apilevel
String constant stating the supported DB API level. For `psycopg2` is
``2.0``.
.. data:: threadsafety
Integer constant stating the level of thread safety the interface
supports. For `psycopg2` is ``2``, i.e. threads can share the module
and the connection. See :ref:`thread-safety` for details.
.. data:: paramstyle
String constant stating the type of parameter marker formatting expected
by the interface. For `psycopg2` is ``pyformat``. See also
:ref:`query-parameters`.
.. data:: __libpq_version__
Integer constant reporting the version of the ``libpq`` library this
``psycopg2`` module was compiled with (in the same format of
`~psycopg2.extensions.ConnectionInfo.server_version`). If this value is
greater or equal than ``90100`` then you may query the version of the
actually loaded library using the `~psycopg2.extensions.libpq_version()`
function.
.. index::
single: Exceptions; DB API
.. _dbapi-exceptions:
Exceptions
----------
In compliance with the |DBAPI|_, the module makes informations about errors
available through the following exceptions:
.. exception:: Warning
Exception raised for important warnings like data truncations while
inserting, etc. It is a subclass of the Python `StandardError`
(`Exception` on Python 3).
.. exception:: Error
Exception that is the base class of all other error exceptions. You can
use this to catch all errors with one single `!except` statement. Warnings
are not considered errors and thus not use this class as base. It
is a subclass of the Python `StandardError` (`Exception` on Python 3).
.. attribute:: pgerror
String representing the error message returned by the backend,
`!None` if not available.
.. attribute:: pgcode
String representing the error code returned by the backend, `!None`
if not available. The `~psycopg2.errorcodes` module contains
symbolic constants representing PostgreSQL error codes.
.. doctest::
:options: +NORMALIZE_WHITESPACE
>>> try:
... cur.execute("SELECT * FROM barf")
... except psycopg2.Error as e:
... pass
>>> e.pgcode
'42P01'
>>> print e.pgerror
ERROR: relation "barf" does not exist
LINE 1: SELECT * FROM barf
^
.. attribute:: cursor
The cursor the exception was raised from; `None` if not applicable.
.. attribute:: diag
A `~psycopg2.extensions.Diagnostics` object containing further
information about the error. ::
>>> try:
... cur.execute("SELECT * FROM barf")
... except psycopg2.Error, e:
... pass
>>> e.diag.severity
'ERROR'
>>> e.diag.message_primary
'relation "barf" does not exist'
.. versionadded:: 2.5
.. extension::
The `~Error.pgerror`, `~Error.pgcode`, `~Error.cursor`, and
`~Error.diag` attributes are Psycopg extensions.
.. exception:: InterfaceError
Exception raised for errors that are related to the database interface
rather than the database itself. It is a subclass of `Error`.
.. exception:: DatabaseError
Exception raised for errors that are related to the database. It is a
subclass of `Error`.
.. exception:: DataError
Exception raised for errors that are due to problems with the processed
data like division by zero, numeric value out of range, etc. It is a
subclass of `DatabaseError`.
.. exception:: OperationalError
Exception raised for errors that are related to the database's operation
and not necessarily under the control of the programmer, e.g. an
unexpected disconnect occurs, the data source name is not found, a
transaction could not be processed, a memory allocation error occurred
during processing, etc. It is a subclass of `DatabaseError`.
.. exception:: IntegrityError
Exception raised when the relational integrity of the database is
affected, e.g. a foreign key check fails. It is a subclass of
`DatabaseError`.
.. exception:: InternalError
Exception raised when the database encounters an internal error, e.g. the
cursor is not valid anymore, the transaction is out of sync, etc. It is a
subclass of `DatabaseError`.
.. exception:: ProgrammingError
Exception raised for programming errors, e.g. table not found or already
exists, syntax error in the SQL statement, wrong number of parameters
specified, etc. It is a subclass of `DatabaseError`.
.. exception:: NotSupportedError
Exception raised in case a method or database API was used which is not
supported by the database, e.g. requesting a `!rollback()` on a
connection that does not support transaction or has transactions turned
off. It is a subclass of `DatabaseError`.
.. extension::
Psycopg actually raises a different exception for each :sql:`SQLSTATE`
error returned by the database: the classes are available in the
`psycopg2.errors` module. Every exception class is a subclass of one of
the exception classes defined here though, so they don't need to be
trapped specifically: trapping `!Error` or `!DatabaseError` is usually
what needed to write a generic error handler; trapping a specific error
such as `!NotNullViolation` can be useful to write specific exception
handlers.
This is the exception inheritance layout:
.. parsed-literal::
`!StandardError`
\|__ `Warning`
\|__ `Error`
\|__ `InterfaceError`
\|__ `DatabaseError`
\|__ `DataError`
\|__ `OperationalError`
\|__ `IntegrityError`
\|__ `InternalError`
\|__ `ProgrammingError`
\|__ `NotSupportedError`
.. _type-objects-and-constructors:
Type Objects and Constructors
-----------------------------
.. note::
This section is mostly copied verbatim from the |DBAPI|_
specification. While these objects are exposed in compliance to the
DB API, Psycopg offers very accurate tools to convert data between Python
and PostgreSQL formats. See :ref:`adapting-new-types` and
:ref:`type-casting-from-sql-to-python`
Many databases need to have the input in a particular format for
binding to an operation's input parameters. For example, if an
input is destined for a DATE column, then it must be bound to the
database in a particular string format. Similar problems exist
for "Row ID" columns or large binary items (e.g. blobs or RAW
columns). This presents problems for Python since the parameters
to the .execute*() method are untyped. When the database module
sees a Python string object, it doesn't know if it should be bound
as a simple CHAR column, as a raw BINARY item, or as a DATE.
To overcome this problem, a module must provide the constructors
defined below to create objects that can hold special values.
When passed to the cursor methods, the module can then detect the
proper type of the input parameter and bind it accordingly.
A Cursor Object's description attribute returns information about
each of the result columns of a query. The type_code must compare
equal to one of Type Objects defined below. Type Objects may be
equal to more than one type code (e.g. DATETIME could be equal to
the type codes for date, time and timestamp columns; see the
Implementation Hints below for details).
The module exports the following constructors and singletons:
.. function:: Date(year,month,day)
This function constructs an object holding a date value.
.. function:: Time(hour,minute,second)
This function constructs an object holding a time value.
.. function:: Timestamp(year,month,day,hour,minute,second)
This function constructs an object holding a time stamp value.
.. function:: DateFromTicks(ticks)
This function constructs an object holding a date value from the given
ticks value (number of seconds since the epoch; see the documentation of
the standard Python time module for details).
.. function:: TimeFromTicks(ticks)
This function constructs an object holding a time value from the given
ticks value (number of seconds since the epoch; see the documentation of
the standard Python time module for details).
.. function:: TimestampFromTicks(ticks)
This function constructs an object holding a time stamp value from the
given ticks value (number of seconds since the epoch; see the
documentation of the standard Python time module for details).
.. function:: Binary(string)
This function constructs an object capable of holding a binary (long)
string value.
.. note::
All the adapters returned by the module level factories (`!Binary`,
`!Date`, `!Time`, `!Timestamp` and the `!*FromTicks` variants) expose the
wrapped object (a regular Python object such as `!datetime`) in an
`!adapted` attribute.
.. data:: STRING
This type object is used to describe columns in a database that are
string-based (e.g. CHAR).
.. data:: BINARY
This type object is used to describe (long) binary columns in a database
(e.g. LONG, RAW, BLOBs).
.. data:: NUMBER
This type object is used to describe numeric columns in a database.
.. data:: DATETIME
This type object is used to describe date/time columns in a database.
.. data:: ROWID
This type object is used to describe the "Row ID" column in a database.
.. testcode::
:hide:
conn.rollback()
Mini Shell