1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
|
The ``connection`` class
========================
.. sectionauthor:: Daniele Varrazzo <daniele.varrazzo@gmail.com>
.. testsetup::
from pprint import pprint
import psycopg2.extensions
drop_test_table('foo')
.. class:: connection
Handles the connection to a PostgreSQL database instance. It encapsulates
a database session.
Connections are created using the factory function
`~psycopg2.connect()`.
Connections are thread safe and can be shared among many threads. See
:ref:`thread-safety` for details.
.. method:: cursor(name=None, cursor_factory=None, scrollable=None, withhold=False)
Return a new `cursor` object using the connection.
If *name* is specified, the returned cursor will be a :ref:`server
side cursor <server-side-cursors>` (also known as *named cursor*).
Otherwise it will be a regular *client side* cursor. By default a
named cursor is declared without :sql:`SCROLL` option and
:sql:`WITHOUT HOLD`: set the argument or property `~cursor.scrollable`
to `!True`/`!False` and or `~cursor.withhold` to `!True` to change the
declaration.
The name can be a string not valid as a PostgreSQL identifier: for
example it may start with a digit and contain non-alphanumeric
characters and quotes.
.. versionchanged:: 2.4
previously only valid PostgreSQL identifiers were accepted as
cursor name.
The *cursor_factory* argument can be used to create non-standard
cursors. The class returned must be a subclass of
`psycopg2.extensions.cursor`. See :ref:`subclassing-cursor` for
details. A default factory for the connection can also be specified
using the `~connection.cursor_factory` attribute.
.. versionchanged:: 2.4.3 added the *withhold* argument.
.. versionchanged:: 2.5 added the *scrollable* argument.
.. extension::
All the function arguments are Psycopg extensions to the |DBAPI|.
.. index::
pair: Transaction; Commit
.. method:: commit()
Commit any pending transaction to the database.
By default, Psycopg opens a transaction before executing the first
command: if `!commit()` is not called, the effect of any data
manipulation will be lost.
The connection can be also set in "autocommit" mode: no transaction is
automatically open, commands have immediate effect. See
:ref:`transactions-control` for details.
.. versionchanged:: 2.5 if the connection is used in a ``with``
statement, the method is automatically called if no exception is
raised in the ``with`` block.
.. index::
pair: Transaction; Rollback
.. method:: rollback()
Roll back to the start of any pending transaction. Closing a
connection without committing the changes first will cause an implicit
rollback to be performed.
.. versionchanged:: 2.5 if the connection is used in a ``with``
statement, the method is automatically called if an exception is
raised in the ``with`` block.
.. method:: close()
Close the connection now (rather than whenever `del` is executed).
The connection will be unusable from this point forward; an
`~psycopg2.InterfaceError` will be raised if any operation is
attempted with the connection. The same applies to all cursor objects
trying to use the connection. Note that closing a connection without
committing the changes first will cause any pending change to be
discarded as if a :sql:`ROLLBACK` was performed (unless a different
isolation level has been selected: see
`~connection.set_isolation_level()`).
.. index::
single: PgBouncer; unclean server
.. versionchanged:: 2.2
previously an explicit :sql:`ROLLBACK` was issued by Psycopg on
`!close()`. The command could have been sent to the backend at an
inappropriate time, so Psycopg currently relies on the backend to
implicitly discard uncommitted changes. Some middleware are known
to behave incorrectly though when the connection is closed during
a transaction (when `~connection.status` is
`~psycopg2.extensions.STATUS_IN_TRANSACTION`), e.g. PgBouncer_
reports an ``unclean server`` and discards the connection. To
avoid this problem you can ensure to terminate the transaction
with a `~connection.commit()`/`~connection.rollback()` before
closing.
.. _PgBouncer: http://pgbouncer.projects.postgresql.org/
.. index::
single: Exceptions; In the connection class
.. rubric:: Exceptions as connection class attributes
The `!connection` also exposes as attributes the same exceptions
available in the `psycopg2` module. See :ref:`dbapi-exceptions`.
.. index::
single: Two-phase commit; methods
.. rubric:: Two-phase commit support methods
.. versionadded:: 2.3
.. seealso:: :ref:`tpc` for an introductory explanation of these methods.
Note that PostgreSQL supports two-phase commit since release 8.1: these
methods raise `~psycopg2.NotSupportedError` if used with an older version
server.
.. _tpc_methods:
.. method:: xid(format_id, gtrid, bqual)
Returns a `~psycopg2.extensions.Xid` instance to be passed to the
`!tpc_*()` methods of this connection. The argument types and
constraints are explained in :ref:`tpc`.
The values passed to the method will be available on the returned
object as the members `~psycopg2.extensions.Xid.format_id`,
`~psycopg2.extensions.Xid.gtrid`, `~psycopg2.extensions.Xid.bqual`.
The object also allows accessing to these members and unpacking as a
3-items tuple.
.. method:: tpc_begin(xid)
Begins a TPC transaction with the given transaction ID *xid*.
This method should be called outside of a transaction (i.e. nothing
may have executed since the last `~connection.commit()` or
`~connection.rollback()` and `connection.status` is
`~psycopg2.extensions.STATUS_READY`).
Furthermore, it is an error to call `!commit()` or `!rollback()`
within the TPC transaction: in this case a `~psycopg2.ProgrammingError`
is raised.
The *xid* may be either an object returned by the `~connection.xid()`
method or a plain string: the latter allows to create a transaction
using the provided string as PostgreSQL transaction id. See also
`~connection.tpc_recover()`.
.. index::
pair: Transaction; Prepare
.. method:: tpc_prepare()
Performs the first phase of a transaction started with
`~connection.tpc_begin()`. A `~psycopg2.ProgrammingError` is raised if
this method is used outside of a TPC transaction.
After calling `!tpc_prepare()`, no statements can be executed until
`~connection.tpc_commit()` or `~connection.tpc_rollback()` will be
called. The `~connection.reset()` method can be used to restore the
status of the connection to `~psycopg2.extensions.STATUS_READY`: the
transaction will remain prepared in the database and will be
possible to finish it with `!tpc_commit(xid)` and
`!tpc_rollback(xid)`.
.. seealso:: the |PREPARE TRANSACTION|_ PostgreSQL command.
.. |PREPARE TRANSACTION| replace:: :sql:`PREPARE TRANSACTION`
.. _PREPARE TRANSACTION: https://www.postgresql.org/docs/current/static/sql-prepare-transaction.html
.. index::
pair: Commit; Prepared
.. method:: tpc_commit([xid])
When called with no arguments, `!tpc_commit()` commits a TPC
transaction previously prepared with `~connection.tpc_prepare()`.
If `!tpc_commit()` is called prior to `!tpc_prepare()`, a single phase
commit is performed. A transaction manager may choose to do this if
only a single resource is participating in the global transaction.
When called with a transaction ID *xid*, the database commits
the given transaction. If an invalid transaction ID is
provided, a `~psycopg2.ProgrammingError` will be raised. This form
should be called outside of a transaction, and is intended for use in
recovery.
On return, the TPC transaction is ended.
.. seealso:: the |COMMIT PREPARED|_ PostgreSQL command.
.. |COMMIT PREPARED| replace:: :sql:`COMMIT PREPARED`
.. _COMMIT PREPARED: https://www.postgresql.org/docs/current/static/sql-commit-prepared.html
.. index::
pair: Rollback; Prepared
.. method:: tpc_rollback([xid])
When called with no arguments, `!tpc_rollback()` rolls back a TPC
transaction. It may be called before or after
`~connection.tpc_prepare()`.
When called with a transaction ID *xid*, it rolls back the given
transaction. If an invalid transaction ID is provided, a
`~psycopg2.ProgrammingError` is raised. This form should be called
outside of a transaction, and is intended for use in recovery.
On return, the TPC transaction is ended.
.. seealso:: the |ROLLBACK PREPARED|_ PostgreSQL command.
.. |ROLLBACK PREPARED| replace:: :sql:`ROLLBACK PREPARED`
.. _ROLLBACK PREPARED: https://www.postgresql.org/docs/current/static/sql-rollback-prepared.html
.. index::
pair: Transaction; Recover
.. method:: tpc_recover()
Returns a list of `~psycopg2.extensions.Xid` representing pending
transactions, suitable for use with `tpc_commit()` or
`tpc_rollback()`.
If a transaction was not initiated by Psycopg, the returned Xids will
have attributes `~psycopg2.extensions.Xid.format_id` and
`~psycopg2.extensions.Xid.bqual` set to `!None` and the
`~psycopg2.extensions.Xid.gtrid` set to the PostgreSQL transaction ID: such Xids are still
usable for recovery. Psycopg uses the same algorithm of the
`PostgreSQL JDBC driver`__ to encode a XA triple in a string, so
transactions initiated by a program using such driver should be
unpacked correctly.
.. __: https://jdbc.postgresql.org/
Xids returned by `!tpc_recover()` also have extra attributes
`~psycopg2.extensions.Xid.prepared`, `~psycopg2.extensions.Xid.owner`,
`~psycopg2.extensions.Xid.database` populated with the values read
from the server.
.. seealso:: the |pg_prepared_xacts|_ system view.
.. |pg_prepared_xacts| replace:: `pg_prepared_xacts`
.. _pg_prepared_xacts: https://www.postgresql.org/docs/current/static/view-pg-prepared-xacts.html
.. extension::
The above methods are the only ones defined by the |DBAPI| protocol.
The Psycopg connection objects exports the following additional
methods and attributes.
.. attribute:: closed
Read-only integer attribute: 0 if the connection is open, nonzero if
it is closed or broken.
.. method:: cancel
Cancel the current database operation.
The method interrupts the processing of the current operation. If no
query is being executed, it does nothing. You can call this function
from a different thread than the one currently executing a database
operation, for instance if you want to cancel a long running query if a
button is pushed in the UI. Interrupting query execution will cause the
cancelled method to raise a
`~psycopg2.extensions.QueryCanceledError`. Note that the termination
of the query is not guaranteed to succeed: see the documentation for
|PQcancel|_.
.. |PQcancel| replace:: `!PQcancel()`
.. _PQcancel: https://www.postgresql.org/docs/current/static/libpq-cancel.html#LIBPQ-PQCANCEL
.. versionadded:: 2.3
.. method:: reset
Reset the connection to the default.
The method rolls back an eventual pending transaction and executes the
PostgreSQL |RESET|_ and |SET SESSION AUTHORIZATION|__ to revert the
session to the default values. A two-phase commit transaction prepared
using `~connection.tpc_prepare()` will remain in the database
available for recover.
.. |RESET| replace:: :sql:`RESET`
.. _RESET: https://www.postgresql.org/docs/current/static/sql-reset.html
.. |SET SESSION AUTHORIZATION| replace:: :sql:`SET SESSION AUTHORIZATION`
.. __: https://www.postgresql.org/docs/current/static/sql-set-session-authorization.html
.. versionadded:: 2.0.12
.. attribute:: dsn
Read-only string containing the connection string used by the
connection.
If a password was specified in the connection string it will be
obscured.
.. rubric:: Transaction control methods and attributes.
.. index::
pair: Transaction; Autocommit
pair: Transaction; Isolation level
.. method:: set_session(isolation_level=None, readonly=None, deferrable=None, autocommit=None)
Set one or more parameters for the next transactions or statements in
the current session.
:param isolation_level: set the `isolation level`_ for the next
transactions/statements. The value can be one of the literal
values ``READ UNCOMMITTED``, ``READ COMMITTED``, ``REPEATABLE
READ``, ``SERIALIZABLE`` or the equivalent :ref:`constant
<isolation-level-constants>` defined in the `~psycopg2.extensions`
module.
:param readonly: if `!True`, set the connection to read only;
read/write if `!False`.
:param deferrable: if `!True`, set the connection to deferrable;
non deferrable if `!False`. Only available from PostgreSQL 9.1.
:param autocommit: switch the connection to autocommit mode: not a
PostgreSQL session setting but an alias for setting the
`autocommit` attribute.
.. _isolation level:
https://www.postgresql.org/docs/current/static/transaction-iso.html
Arguments set to `!None` (the default for all) will not be changed.
The parameters *isolation_level*, *readonly* and *deferrable* also
accept the string ``DEFAULT`` as a value: the effect is to reset the
parameter to the server default. Defaults are defined by the server
configuration: see values for |default_transaction_isolation|__,
|default_transaction_read_only|__, |default_transaction_deferrable|__.
.. |default_transaction_isolation| replace:: :sql:`default_transaction_isolation`
.. __: https://www.postgresql.org/docs/current/static/runtime-config-client.html#GUC-DEFAULT-TRANSACTION-ISOLATION
.. |default_transaction_read_only| replace:: :sql:`default_transaction_read_only`
.. __: https://www.postgresql.org/docs/current/static/runtime-config-client.html#GUC-DEFAULT-TRANSACTION-READ-ONLY
.. |default_transaction_deferrable| replace:: :sql:`default_transaction_deferrable`
.. __: https://www.postgresql.org/docs/current/static/runtime-config-client.html#GUC-DEFAULT-TRANSACTION-DEFERRABLE
The function must be invoked with no transaction in progress.
.. seealso:: |SET TRANSACTION|_ for further details about the behaviour
of the transaction parameters in the server.
.. |SET TRANSACTION| replace:: :sql:`SET TRANSACTION`
.. _SET TRANSACTION: https://www.postgresql.org/docs/current/static/sql-set-transaction.html
.. versionadded:: 2.4.2
.. versionchanged:: 2.7
Before this version, the function would have set
:sql:`default_transaction_*` attribute in the current session;
this implementation has the problem of not playing well with
external connection pooling working at transaction level and not
resetting the state of the session: changing the default
transaction would pollute the connections in the pool and create
problems to other applications using the same pool.
Starting from 2.7, if the connection is not autocommit, the
transaction characteristics are issued together with :sql:`BEGIN`
and will leave the :sql:`default_transaction_*` settings untouched.
For example::
conn.set_session(readonly=True)
will not change :sql:`default_transaction_read_only`, but
following transaction will start with a :sql:`BEGIN READ ONLY`.
Conversely, using::
conn.set_session(readonly=True, autocommit=True)
will set :sql:`default_transaction_read_only` to :sql:`on` and
rely on the server to apply the read only state to whatever
transaction, implicit or explicit, is executed in the connection.
.. attribute:: autocommit
Read/write attribute: if `!True`, no transaction is handled by the
driver and every statement sent to the backend has immediate effect;
if `!False` a new transaction is started at the first command
execution: the methods `commit()` or `rollback()` must be manually
invoked to terminate the transaction.
The autocommit mode is useful to execute commands requiring to be run
outside a transaction, such as :sql:`CREATE DATABASE` or
:sql:`VACUUM`.
The default is `!False` (manual commit) as per DBAPI specification.
.. warning::
By default, any query execution, including a simple :sql:`SELECT`
will start a transaction: for long-running programs, if no further
action is taken, the session will remain "idle in transaction", an
undesirable condition for several reasons (locks are held by
the session, tables bloat...). For long lived scripts, either
ensure to terminate a transaction as soon as possible or use an
autocommit connection.
.. versionadded:: 2.4.2
.. attribute:: isolation_level
Return or set the `transaction isolation level`_ for the current
session. The value is one of the :ref:`isolation-level-constants`
defined in the `psycopg2.extensions` module. On set it is also
possible to use one of the literal values ``READ UNCOMMITTED``, ``READ
COMMITTED``, ``REPEATABLE READ``, ``SERIALIZABLE``, ``DEFAULT``.
.. versionchanged:: 2.7
the property is writable.
.. versionchanged:: 2.7
the default value for `!isolation_level` is
`~psycopg2.extensions.ISOLATION_LEVEL_DEFAULT`; previously the
property would have queried the server and returned the real value
applied. To know this value you can run a query such as :sql:`show
transaction_isolation`. Usually the default value is `READ
COMMITTED`, but this may be changed in the server configuration.
This value is now entirely separate from the `autocommit`
property: in previous version, if `!autocommit` was set to `!True`
this property would have returned
`~psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT`; it will now
return the server isolation level.
.. attribute:: readonly
Return or set the read-only status for the current session. Available
values are `!True` (new transactions will be in read-only mode),
`!False` (new transactions will be writable), `!None` (use the default
configured for the server by :sql:`default_transaction_read_only`).
.. versionadded:: 2.7
.. attribute:: deferrable
Return or set the `deferrable status`__ for the current session.
Available values are `!True` (new transactions will be in deferrable
mode), `!False` (new transactions will be in non deferrable mode),
`!None` (use the default configured for the server by
:sql:`default_transaction_deferrable`).
.. __: `SET TRANSACTION`_
.. versionadded:: 2.7
.. method:: set_isolation_level(level)
.. note::
This is a legacy method mixing `~conn.isolation_level` and
`~conn.autocommit`. Using the respective properties is a better
option.
Set the `transaction isolation level`_ for the current session.
The level defines the different phenomena that can happen in the
database between concurrent transactions.
The value set is an integer: symbolic constants are defined in
the module `psycopg2.extensions`: see
:ref:`isolation-level-constants` for the available values.
The default level is `~psycopg2.extensions.ISOLATION_LEVEL_DEFAULT`:
at this level a transaction is automatically started the first time a
database command is executed. If you want an *autocommit* mode,
switch to `~psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT` before
executing any command::
>>> conn.set_isolation_level(psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT)
See also :ref:`transactions-control`.
.. index::
pair: Client; Encoding
.. attribute:: encoding
.. method:: set_client_encoding(enc)
Read or set the client encoding for the current session. The default
is the encoding defined by the database. It should be one of the
`characters set supported by PostgreSQL`__
.. __: https://www.postgresql.org/docs/current/static/multibyte.html
.. index::
pair: Client; Logging
.. attribute:: notices
A list containing all the database messages sent to the client during
the session.
.. doctest::
:options: +NORMALIZE_WHITESPACE
>>> cur.execute("CREATE TABLE foo (id serial PRIMARY KEY);")
>>> pprint(conn.notices)
['NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "foo_pkey" for table "foo"\n',
'NOTICE: CREATE TABLE will create implicit sequence "foo_id_seq" for serial column "foo.id"\n']
.. versionchanged:: 2.7
The `!notices` attribute is writable: the user may replace it
with any Python object exposing an `!append()` method. If
appending raises an exception the notice is silently
dropped.
To avoid a leak in case excessive notices are generated, only the last
50 messages are kept. This check is only in place if the `!notices`
attribute is a list: if any other object is used it will be up to the
user to guard from leakage.
You can configure what messages to receive using `PostgreSQL logging
configuration parameters`__ such as ``log_statement``,
``client_min_messages``, ``log_min_duration_statement`` etc.
.. __: https://www.postgresql.org/docs/current/static/runtime-config-logging.html
.. attribute:: notifies
List of `~psycopg2.extensions.Notify` objects containing asynchronous
notifications received by the session.
For other details see :ref:`async-notify`.
.. versionchanged:: 2.3
Notifications are instances of the `!Notify` object. Previously the
list was composed by 2 items tuples :samp:`({pid},{channel})` and
the payload was not accessible. To keep backward compatibility,
`!Notify` objects can still be accessed as 2 items tuples.
.. versionchanged:: 2.7
The `!notifies` attribute is writable: the user may replace it
with any Python object exposing an `!append()` method. If
appending raises an exception the notification is silently
dropped.
.. attribute:: cursor_factory
The default cursor factory used by `~connection.cursor()` if the
parameter is not specified.
.. versionadded:: 2.5
.. index::
pair: Connection; Info
.. attribute:: info
A `~psycopg2.extensions.ConnectionInfo` object exposing information
about the native libpq connection.
.. versionadded:: 2.8.0
.. index::
pair: Connection; Parameters
.. method:: get_dsn_parameters()
Get the effective dsn parameters for the connection as a dictionary.
The *password* parameter is removed from the result.
Example::
>>> conn.get_dsn_parameters()
{'dbname': 'test', 'user': 'postgres', 'port': '5432', 'sslmode': 'prefer'}
Requires libpq >= 9.3.
.. seealso:: libpq docs for `PQconninfo()`__ for details.
.. __: https://www.postgresql.org/docs/current/static/libpq-connect.html#LIBPQ-PQCONNINFO
.. versionadded:: 2.7
.. index::
pair: Connection; Status
.. attribute:: status
A read-only integer representing the status of the connection.
Symbolic constants for the values are defined in the module
`psycopg2.extensions`: see :ref:`connection-status-constants`
for the available values.
The status is undefined for `closed` connections.
.. method:: lobject([oid [, mode [, new_oid [, new_file [, lobject_factory]]]]])
Return a new database large object as a `~psycopg2.extensions.lobject`
instance.
See :ref:`large-objects` for an overview.
:param oid: The OID of the object to read or write. 0 to create
a new large object and and have its OID assigned automatically.
:param mode: Access mode to the object, see below.
:param new_oid: Create a new object using the specified OID. The
function raises `~psycopg2.OperationalError` if the OID is already
in use. Default is 0, meaning assign a new one automatically.
:param new_file: The name of a file to be imported in the the database
(using the |lo_import|_ function)
:param lobject_factory: Subclass of
`~psycopg2.extensions.lobject` to be instantiated.
.. |lo_import| replace:: `!lo_import()`
.. _lo_import: https://www.postgresql.org/docs/current/static/lo-interfaces.html#LO-IMPORT
Available values for *mode* are:
======= =========
*mode* meaning
======= =========
``r`` Open for read only
``w`` Open for write only
``rw`` Open for read/write
``n`` Don't open the file
``b`` Don't decode read data (return data as `!str` in Python 2 or `!bytes` in Python 3)
``t`` Decode read data according to `connection.encoding` (return data as `!unicode` in Python 2 or `!str` in Python 3)
======= =========
``b`` and ``t`` can be specified together with a read/write mode. If
neither ``b`` nor ``t`` is specified, the default is ``b`` in Python 2
and ``t`` in Python 3.
.. versionadded:: 2.0.8
.. versionchanged:: 2.4 added ``b`` and ``t`` mode and unicode
support.
.. rubric:: Methods related to asynchronous support
.. versionadded:: 2.2.0
.. seealso:: :ref:`async-support` and :ref:`green-support`.
.. attribute:: async
async_
Read only attribute: 1 if the connection is asynchronous, 0 otherwise.
.. versionchanged:: 2.7 added the `!async_` alias for Python versions
where `!async` is a keyword.
.. method:: poll()
Used during an asynchronous connection attempt, or when a cursor is
executing a query on an asynchronous connection, make communication
proceed if it wouldn't block.
Return one of the constants defined in :ref:`poll-constants`. If it
returns `~psycopg2.extensions.POLL_OK` then the connection has been
established or the query results are available on the client.
Otherwise wait until the file descriptor returned by `fileno()` is
ready to read or to write, as explained in :ref:`async-support`.
`poll()` should be also used by the function installed by
`~psycopg2.extensions.set_wait_callback()` as explained in
:ref:`green-support`.
`poll()` is also used to receive asynchronous notifications from the
database: see :ref:`async-notify` from further details.
.. method:: fileno()
Return the file descriptor underlying the connection: useful to read
its status during asynchronous communication.
.. method:: isexecuting()
Return `!True` if the connection is executing an asynchronous operation.
.. rubric:: Interoperation with other C API modules
.. attribute:: pgconn_ptr
Return the internal `!PGconn*` as integer. Useful to pass the libpq
raw connection structure to C functions, e.g. via `ctypes`::
>>> import ctypes
>>> libpq = ctypes.pydll.LoadLibrary(ctypes.util.find_library('pq'))
>>> libpq.PQserverVersion.argtypes = [ctypes.c_void_p]
>>> libpq.PQserverVersion.restype = ctypes.c_int
>>> libpq.PQserverVersion(conn.pgconn_ptr)
90611
.. versionadded:: 2.8
.. method:: get_native_connection()
Return the internal `!PGconn*` wrapped in a PyCapsule object. This is
only useful for passing the `libpq` raw connection associated to this
connection object to other C-level modules that may have a use for it.
.. seealso:: Python C API `Capsules`__ docs.
.. __: https://docs.python.org/3.1/c-api/capsule.html
.. versionadded:: 2.8
.. rubric:: informative methods of the native connection
.. note::
These methods are better accessed using the `~connection.info`
attributes and may be dropped in future versions.
.. index::
pair: Transaction; Status
.. method:: get_transaction_status()
Also available as `~connection.info`\ `!.`\
`~psycopg2.extensions.ConnectionInfo.transaction_status`.
Return the current session transaction status as an integer. Symbolic
constants for the values are defined in the module
`psycopg2.extensions`: see :ref:`transaction-status-constants`
for the available values.
.. seealso:: libpq docs for `PQtransactionStatus()`__ for details.
.. __: https://www.postgresql.org/docs/current/static/libpq-status.html#LIBPQ-PQTRANSACTIONSTATUS
.. index::
pair: Protocol; Version
.. attribute:: protocol_version
Also available as `~connection.info`\ `!.`\
`~psycopg2.extensions.ConnectionInfo.protocol_version`.
A read-only integer representing frontend/backend protocol being used.
Currently Psycopg supports only protocol 3, which allows connection
to PostgreSQL server from version 7.4. Psycopg versions previous than
2.3 support both protocols 2 and 3.
.. seealso:: libpq docs for `PQprotocolVersion()`__ for details.
.. __: https://www.postgresql.org/docs/current/static/libpq-status.html#LIBPQ-PQPROTOCOLVERSION
.. versionadded:: 2.0.12
.. index::
pair: Server; Version
.. attribute:: server_version
Also available as `~connection.info`\ `!.`\
`~psycopg2.extensions.ConnectionInfo.server_version`.
A read-only integer representing the backend version.
The number is formed by converting the major, minor, and revision
numbers into two-decimal-digit numbers and appending them together.
For example, version 8.1.5 will be returned as ``80105``.
.. seealso:: libpq docs for `PQserverVersion()`__ for details.
.. __: https://www.postgresql.org/docs/current/static/libpq-status.html#LIBPQ-PQSERVERVERSION
.. versionadded:: 2.0.12
.. index::
pair: Backend; PID
.. method:: get_backend_pid()
Also available as `~connection.info`\ `!.`\
`~psycopg2.extensions.ConnectionInfo.backend_pid`.
Returns the process ID (PID) of the backend server process handling
this connection.
Note that the PID belongs to a process executing on the database
server host, not the local host!
.. seealso:: libpq docs for `PQbackendPID()`__ for details.
.. __: https://www.postgresql.org/docs/current/static/libpq-status.html#LIBPQ-PQBACKENDPID
.. versionadded:: 2.0.8
.. index::
pair: Server; Parameters
.. method:: get_parameter_status(parameter)
Also available as `~connection.info`\ `!.`\
`~psycopg2.extensions.ConnectionInfo.parameter_status()`.
Look up a current parameter setting of the server.
Potential values for ``parameter`` are: ``server_version``,
``server_encoding``, ``client_encoding``, ``is_superuser``,
``session_authorization``, ``DateStyle``, ``TimeZone``,
``integer_datetimes``, and ``standard_conforming_strings``.
If server did not report requested parameter, return `!None`.
.. seealso:: libpq docs for `PQparameterStatus()`__ for details.
.. __: https://www.postgresql.org/docs/current/static/libpq-status.html#LIBPQ-PQPARAMETERSTATUS
.. versionadded:: 2.0.12
.. testcode::
:hide:
conn.rollback()
|