summaryrefslogtreecommitdiffstats
path: root/Doc/library/sqlite3.rst
blob: 605d8d36b7b962713c6f9ad5ac52f9ce1830e451 (plain)
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
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
:mod:`sqlite3` --- DB-API 2.0 interface for SQLite databases
============================================================

.. module:: sqlite3
   :synopsis: A DB-API 2.0 implementation using SQLite 3.x.

.. sectionauthor:: Gerhard Häring <gh@ghaering.de>

**Source code:** :source:`Lib/sqlite3/`

--------------

SQLite is a C library that provides a lightweight disk-based database that
doesn't require a separate server process and allows accessing the database
using a nonstandard variant of the SQL query language. Some applications can use
SQLite for internal data storage.  It's also possible to prototype an
application using SQLite and then port the code to a larger database such as
PostgreSQL or Oracle.

The sqlite3 module was written by Gerhard Häring.  It provides a SQL interface
compliant with the DB-API 2.0 specification described by :pep:`249`.

To use the module, you must first create a :class:`Connection` object that
represents the database.  Here the data will be stored in the
:file:`example.db` file::

   import sqlite3
   conn = sqlite3.connect('example.db')

You can also supply the special name ``:memory:`` to create a database in RAM.

Once you have a :class:`Connection`, you can create a :class:`Cursor`  object
and call its :meth:`~Cursor.execute` method to perform SQL commands::

   c = conn.cursor()

   # Create table
   c.execute('''CREATE TABLE stocks
                (date text, trans text, symbol text, qty real, price real)''')

   # Insert a row of data
   c.execute("INSERT INTO stocks VALUES ('2006-01-05','BUY','RHAT',100,35.14)")

   # Save (commit) the changes
   conn.commit()

   # We can also close the connection if we are done with it.
   # Just be sure any changes have been committed or they will be lost.
   conn.close()

The data you've saved is persistent and is available in subsequent sessions::

   import sqlite3
   conn = sqlite3.connect('example.db')
   c = conn.cursor()

Usually your SQL operations will need to use values from Python variables.  You
shouldn't assemble your query using Python's string operations because doing so
is insecure; it makes your program vulnerable to an SQL injection attack
(see https://xkcd.com/327/ for humorous example of what can go wrong).

Instead, use the DB-API's parameter substitution.  Put ``?`` as a placeholder
wherever you want to use a value, and then provide a tuple of values as the
second argument to the cursor's :meth:`~Cursor.execute` method.  (Other database
modules may use a different placeholder, such as ``%s`` or ``:1``.) For
example::

   # Never do this -- insecure!
   symbol = 'RHAT'
   c.execute("SELECT * FROM stocks WHERE symbol = '%s'" % symbol)

   # Do this instead
   t = ('RHAT',)
   c.execute('SELECT * FROM stocks WHERE symbol=?', t)
   print(c.fetchone())

   # Larger example that inserts many records at a time
   purchases = [('2006-03-28', 'BUY', 'IBM', 1000, 45.00),
                ('2006-04-05', 'BUY', 'MSFT', 1000, 72.00),
                ('2006-04-06', 'SELL', 'IBM', 500, 53.00),
               ]
   c.executemany('INSERT INTO stocks VALUES (?,?,?,?,?)', purchases)

To retrieve data after executing a SELECT statement, you can either treat the
cursor as an :term:`iterator`, call the cursor's :meth:`~Cursor.fetchone` method to
retrieve a single matching row, or call :meth:`~Cursor.fetchall` to get a list of the
matching rows.

This example uses the iterator form::

   >>> for row in c.execute('SELECT * FROM stocks ORDER BY price'):
           print(row)

   ('2006-01-05', 'BUY', 'RHAT', 100, 35.14)
   ('2006-03-28', 'BUY', 'IBM', 1000, 45.0)
   ('2006-04-06', 'SELL', 'IBM', 500, 53.0)
   ('2006-04-05', 'BUY', 'MSFT', 1000, 72.0)


.. seealso::

   https://github.com/ghaering/pysqlite
      The pysqlite web page -- sqlite3 is developed externally under the name
      "pysqlite".

   https://www.sqlite.org
      The SQLite web page; the documentation describes the syntax and the
      available data types for the supported SQL dialect.

   http://www.w3schools.com/sql/
      Tutorial, reference and examples for learning SQL syntax.

   :pep:`249` - Database API Specification 2.0
      PEP written by Marc-André Lemburg.


.. _sqlite3-module-contents:

Module functions and constants
------------------------------


.. data:: version

   The version number of this module, as a string. This is not the version of
   the SQLite library.


.. data:: version_info

   The version number of this module, as a tuple of integers. This is not the
   version of the SQLite library.


.. data:: sqlite_version

   The version number of the run-time SQLite library, as a string.


.. data:: sqlite_version_info

   The version number of the run-time SQLite library, as a tuple of integers.


.. data:: PARSE_DECLTYPES

   This constant is meant to be used with the *detect_types* parameter of the
   :func:`connect` function.

   Setting it makes the :mod:`sqlite3` module parse the declared type for each
   column it returns.  It will parse out the first word of the declared type,
   i. e.  for "integer primary key", it will parse out "integer", or for
   "number(10)" it will parse out "number". Then for that column, it will look
   into the converters dictionary and use the converter function registered for
   that type there.


.. data:: PARSE_COLNAMES

   This constant is meant to be used with the *detect_types* parameter of the
   :func:`connect` function.

   Setting this makes the SQLite interface parse the column name for each column it
   returns.  It will look for a string formed [mytype] in there, and then decide
   that 'mytype' is the type of the column. It will try to find an entry of
   'mytype' in the converters dictionary and then use the converter function found
   there to return the value. The column name found in :attr:`Cursor.description`
   is only the first word of the column name, i.  e. if you use something like
   ``'as "x [datetime]"'`` in your SQL, then we will parse out everything until the
   first blank for the column name: the column name would simply be "x".


.. function:: connect(database[, timeout, detect_types, isolation_level, check_same_thread, factory, cached_statements, uri])

   Opens a connection to the SQLite database file *database*. You can use
   ``":memory:"`` to open a database connection to a database that resides in RAM
   instead of on disk.

   When a database is accessed by multiple connections, and one of the processes
   modifies the database, the SQLite database is locked until that transaction is
   committed. The *timeout* parameter specifies how long the connection should wait
   for the lock to go away until raising an exception. The default for the timeout
   parameter is 5.0 (five seconds).

   For the *isolation_level* parameter, please see the
   :attr:`Connection.isolation_level` property of :class:`Connection` objects.

   SQLite natively supports only the types TEXT, INTEGER, REAL, BLOB and NULL. If
   you want to use other types you must add support for them yourself. The
   *detect_types* parameter and the using custom **converters** registered with the
   module-level :func:`register_converter` function allow you to easily do that.

   *detect_types* defaults to 0 (i. e. off, no type detection), you can set it to
   any combination of :const:`PARSE_DECLTYPES` and :const:`PARSE_COLNAMES` to turn
   type detection on.

   By default, *check_same_thread* is :const:`True` and only the creating thread may
   use the connection. If set :const:`False`, the returned connection may be shared
   across multiple threads. When using multiple threads with the same connection
   writing operations should be serialized by the user to avoid data corruption.

   By default, the :mod:`sqlite3` module uses its :class:`Connection` class for the
   connect call.  You can, however, subclass the :class:`Connection` class and make
   :func:`connect` use your class instead by providing your class for the *factory*
   parameter.

   Consult the section :ref:`sqlite3-types` of this manual for details.

   The :mod:`sqlite3` module internally uses a statement cache to avoid SQL parsing
   overhead. If you want to explicitly set the number of statements that are cached
   for the connection, you can set the *cached_statements* parameter. The currently
   implemented default is to cache 100 statements.

   If *uri* is true, *database* is interpreted as a URI. This allows you
   to specify options. For example, to open a database in read-only mode
   you can use::

       db = sqlite3.connect('file:path/to/database?mode=ro', uri=True)

   More information about this feature, including a list of recognized options, can
   be found in the `SQLite URI documentation <https://www.sqlite.org/uri.html>`_.

   .. versionchanged:: 3.4
      Added the *uri* parameter.


.. function:: register_converter(typename, callable)

   Registers a callable to convert a bytestring from the database into a custom
   Python type. The callable will be invoked for all database values that are of
   the type *typename*. Confer the parameter *detect_types* of the :func:`connect`
   function for how the type detection works. Note that the case of *typename* and
   the name of the type in your query must match!


.. function:: register_adapter(type, callable)

   Registers a callable to convert the custom Python type *type* into one of
   SQLite's supported types. The callable *callable* accepts as single parameter
   the Python value, and must return a value of the following types: int,
   float, str or bytes.


.. function:: complete_statement(sql)

   Returns :const:`True` if the string *sql* contains one or more complete SQL
   statements terminated by semicolons. It does not verify that the SQL is
   syntactically correct, only that there are no unclosed string literals and the
   statement is terminated by a semicolon.

   This can be used to build a shell for SQLite, as in the following example:


   .. literalinclude:: ../includes/sqlite3/complete_statement.py


.. function:: enable_callback_tracebacks(flag)

   By default you will not get any tracebacks in user-defined functions,
   aggregates, converters, authorizer callbacks etc. If you want to debug them,
   you can call this function with *flag* set to ``True``. Afterwards, you will
   get tracebacks from callbacks on ``sys.stderr``. Use :const:`False` to
   disable the feature again.


.. _sqlite3-connection-objects:

Connection Objects
------------------

.. class:: Connection

   A SQLite database connection has the following attributes and methods:

   .. attribute:: isolation_level

      Get or set the current isolation level. :const:`None` for autocommit mode or
      one of "DEFERRED", "IMMEDIATE" or "EXCLUSIVE". See section
      :ref:`sqlite3-controlling-transactions` for a more detailed explanation.

   .. attribute:: in_transaction

      :const:`True` if a transaction is active (there are uncommitted changes),
      :const:`False` otherwise.  Read-only attribute.

      .. versionadded:: 3.2

   .. method:: cursor([cursorClass])

      The cursor method accepts a single optional parameter *cursorClass*. If
      supplied, this must be a custom cursor class that extends
      :class:`sqlite3.Cursor`.

   .. method:: commit()

      This method commits the current transaction. If you don't call this method,
      anything you did since the last call to ``commit()`` is not visible from
      other database connections. If you wonder why you don't see the data you've
      written to the database, please check you didn't forget to call this method.

   .. method:: rollback()

      This method rolls back any changes to the database since the last call to
      :meth:`commit`.

   .. method:: close()

      This closes the database connection. Note that this does not automatically
      call :meth:`commit`. If you just close your database connection without
      calling :meth:`commit` first, your changes will be lost!

   .. method:: execute(sql[, parameters])

      This is a nonstandard shortcut that creates a cursor object by calling
      the :meth:`~Connection.cursor` method, calls the cursor's
      :meth:`~Cursor.execute` method with the *parameters* given, and returns
      the cursor.

   .. method:: executemany(sql[, parameters])

      This is a nonstandard shortcut that creates a cursor object by
      calling the :meth:`~Connection.cursor` method, calls the cursor's
      :meth:`~Cursor.executemany` method with the *parameters* given, and
      returns the cursor.

   .. method:: executescript(sql_script)

      This is a nonstandard shortcut that creates a cursor object by
      calling the :meth:`~Connection.cursor` method, calls the cursor's
      :meth:`~Cursor.executescript` method with the given *sql_script*, and
      returns the cursor.

   .. method:: create_function(name, num_params, func)

      Creates a user-defined function that you can later use from within SQL
      statements under the function name *name*. *num_params* is the number of
      parameters the function accepts (if *num_params* is -1, the function may
      take any number of arguments), and *func* is a Python callable that is
      called as the SQL function.

      The function can return any of the types supported by SQLite: bytes, str, int,
      float and None.

      Example:

      .. literalinclude:: ../includes/sqlite3/md5func.py


   .. method:: create_aggregate(name, num_params, aggregate_class)

      Creates a user-defined aggregate function.

      The aggregate class must implement a ``step`` method, which accepts the number
      of parameters *num_params* (if *num_params* is -1, the function may take
      any number of arguments), and a ``finalize`` method which will return the
      final result of the aggregate.

      The ``finalize`` method can return any of the types supported by SQLite:
      bytes, str, int, float and None.

      Example:

      .. literalinclude:: ../includes/sqlite3/mysumaggr.py


   .. method:: create_collation(name, callable)

      Creates a collation with the specified *name* and *callable*. The callable will
      be passed two string arguments. It should return -1 if the first is ordered
      lower than the second, 0 if they are ordered equal and 1 if the first is ordered
      higher than the second.  Note that this controls sorting (ORDER BY in SQL) so
      your comparisons don't affect other SQL operations.

      Note that the callable will get its parameters as Python bytestrings, which will
      normally be encoded in UTF-8.

      The following example shows a custom collation that sorts "the wrong way":

      .. literalinclude:: ../includes/sqlite3/collation_reverse.py

      To remove a collation, call ``create_collation`` with None as callable::

         con.create_collation("reverse", None)


   .. method:: interrupt()

      You can call this method from a different thread to abort any queries that might
      be executing on the connection. The query will then abort and the caller will
      get an exception.


   .. method:: set_authorizer(authorizer_callback)

      This routine registers a callback. The callback is invoked for each attempt to
      access a column of a table in the database. The callback should return
      :const:`SQLITE_OK` if access is allowed, :const:`SQLITE_DENY` if the entire SQL
      statement should be aborted with an error and :const:`SQLITE_IGNORE` if the
      column should be treated as a NULL value. These constants are available in the
      :mod:`sqlite3` module.

      The first argument to the callback signifies what kind of operation is to be
      authorized. The second and third argument will be arguments or :const:`None`
      depending on the first argument. The 4th argument is the name of the database
      ("main", "temp", etc.) if applicable. The 5th argument is the name of the
      inner-most trigger or view that is responsible for the access attempt or
      :const:`None` if this access attempt is directly from input SQL code.

      Please consult the SQLite documentation about the possible values for the first
      argument and the meaning of the second and third argument depending on the first
      one. All necessary constants are available in the :mod:`sqlite3` module.


   .. method:: set_progress_handler(handler, n)

      This routine registers a callback. The callback is invoked for every *n*
      instructions of the SQLite virtual machine. This is useful if you want to
      get called from SQLite during long-running operations, for example to update
      a GUI.

      If you want to clear any previously installed progress handler, call the
      method with :const:`None` for *handler*.


   .. method:: set_trace_callback(trace_callback)

      Registers *trace_callback* to be called for each SQL statement that is
      actually executed by the SQLite backend.

      The only argument passed to the callback is the statement (as string) that
      is being executed. The return value of the callback is ignored. Note that
      the backend does not only run statements passed to the :meth:`Cursor.execute`
      methods.  Other sources include the transaction management of the Python
      module and the execution of triggers defined in the current database.

      Passing :const:`None` as *trace_callback* will disable the trace callback.

      .. versionadded:: 3.3


   .. method:: enable_load_extension(enabled)

      This routine allows/disallows the SQLite engine to load SQLite extensions
      from shared libraries.  SQLite extensions can define new functions,
      aggregates or whole new virtual table implementations.  One well-known
      extension is the fulltext-search extension distributed with SQLite.

      Loadable extensions are disabled by default. See [#f1]_.

      .. versionadded:: 3.2

      .. literalinclude:: ../includes/sqlite3/load_extension.py

   .. method:: load_extension(path)

      This routine loads a SQLite extension from a shared library.  You have to
      enable extension loading with :meth:`enable_load_extension` before you can
      use this routine.

      Loadable extensions are disabled by default. See [#f1]_.

      .. versionadded:: 3.2

   .. attribute:: row_factory

      You can change this attribute to a callable that accepts the cursor and the
      original row as a tuple and will return the real result row.  This way, you can
      implement more advanced ways of returning results, such  as returning an object
      that can also access columns by name.

      Example:

      .. literalinclude:: ../includes/sqlite3/row_factory.py

      If returning a tuple doesn't suffice and you want name-based access to
      columns, you should consider setting :attr:`row_factory` to the
      highly-optimized :class:`sqlite3.Row` type. :class:`Row` provides both
      index-based and case-insensitive name-based access to columns with almost no
      memory overhead. It will probably be better than your own custom
      dictionary-based approach or even a db_row based solution.

      .. XXX what's a db_row-based solution?


   .. attribute:: text_factory

      Using this attribute you can control what objects are returned for the ``TEXT``
      data type. By default, this attribute is set to :class:`str` and the
      :mod:`sqlite3` module will return Unicode objects for ``TEXT``. If you want to
      return bytestrings instead, you can set it to :class:`bytes`.

      You can also set it to any other callable that accepts a single bytestring
      parameter and returns the resulting object.

      See the following example code for illustration:

      .. literalinclude:: ../includes/sqlite3/text_factory.py


   .. attribute:: total_changes

      Returns the total number of database rows that have been modified, inserted, or
      deleted since the database connection was opened.


   .. method:: iterdump

      Returns an iterator to dump the database in an SQL text format.  Useful when
      saving an in-memory database for later restoration.  This function provides
      the same capabilities as the :kbd:`.dump` command in the :program:`sqlite3`
      shell.

      Example::

         # Convert file existing_db.db to SQL dump file dump.sql
         import sqlite3

         con = sqlite3.connect('existing_db.db')
         with open('dump.sql', 'w') as f:
             for line in con.iterdump():
                 f.write('%s\n' % line)


.. _sqlite3-cursor-objects:

Cursor Objects
--------------

.. class:: Cursor

   A :class:`Cursor` instance has the following attributes and methods.

   .. method:: execute(sql[, parameters])

      Executes an SQL statement. The SQL statement may be parameterized (i. e.
      placeholders instead of SQL literals). The :mod:`sqlite3` module supports two
      kinds of placeholders: question marks (qmark style) and named placeholders
      (named style).

      Here's an example of both styles:

      .. literalinclude:: ../includes/sqlite3/execute_1.py

      :meth:`execute` will only execute a single SQL statement. If you try to execute
      more than one statement with it, it will raise an ``sqlite3.Warning``. Use
      :meth:`executescript` if you want to execute multiple SQL statements with one
      call.


   .. method:: executemany(sql, seq_of_parameters)

      Executes an SQL command against all parameter sequences or mappings found in
      the sequence *seq_of_parameters*.  The :mod:`sqlite3` module also allows
      using an :term:`iterator` yielding parameters instead of a sequence.

      .. literalinclude:: ../includes/sqlite3/executemany_1.py

      Here's a shorter example using a :term:`generator`:

      .. literalinclude:: ../includes/sqlite3/executemany_2.py


   .. method:: executescript(sql_script)

      This is a nonstandard convenience method for executing multiple SQL statements
      at once. It issues a ``COMMIT`` statement first, then executes the SQL script it
      gets as a parameter.

      *sql_script* can be an instance of :class:`str`.

      Example:

      .. literalinclude:: ../includes/sqlite3/executescript.py


   .. method:: fetchone()

      Fetches the next row of a query result set, returning a single sequence,
      or :const:`None` when no more data is available.


   .. method:: fetchmany(size=cursor.arraysize)

      Fetches the next set of rows of a query result, returning a list.  An empty
      list is returned when no more rows are available.

      The number of rows to fetch per call is specified by the *size* parameter.
      If it is not given, the cursor's arraysize determines the number of rows
      to be fetched. The method should try to fetch as many rows as indicated by
      the size parameter. If this is not possible due to the specified number of
      rows not being available, fewer rows may be returned.

      Note there are performance considerations involved with the *size* parameter.
      For optimal performance, it is usually best to use the arraysize attribute.
      If the *size* parameter is used, then it is best for it to retain the same
      value from one :meth:`fetchmany` call to the next.

   .. method:: fetchall()

      Fetches all (remaining) rows of a query result, returning a list.  Note that
      the cursor's arraysize attribute can affect the performance of this operation.
      An empty list is returned when no rows are available.

   .. method:: close()

      Close the cursor now (rather than whenever ``__del__`` is called).

      The cursor will be unusable from this point forward; a ``ProgrammingError``
      exception will be raised if any operation is attempted with the cursor.

   .. attribute:: rowcount

      Although the :class:`Cursor` class of the :mod:`sqlite3` module implements this
      attribute, the database engine's own support for the determination of "rows
      affected"/"rows selected" is quirky.

      For :meth:`executemany` statements, the number of modifications are summed up
      into :attr:`rowcount`.

      As required by the Python DB API Spec, the :attr:`rowcount` attribute "is -1 in
      case no ``executeXX()`` has been performed on the cursor or the rowcount of the
      last operation is not determinable by the interface". This includes ``SELECT``
      statements because we cannot determine the number of rows a query produced
      until all rows were fetched.

      With SQLite versions before 3.6.5, :attr:`rowcount` is set to 0 if
      you make a ``DELETE FROM table`` without any condition.

   .. attribute:: lastrowid

      This read-only attribute provides the rowid of the last modified row. It is
      only set if you issued an ``INSERT`` statement using the :meth:`execute`
      method. For operations other than ``INSERT`` or when :meth:`executemany` is
      called, :attr:`lastrowid` is set to :const:`None`.

   .. attribute:: description

      This read-only attribute provides the column names of the last query. To
      remain compatible with the Python DB API, it returns a 7-tuple for each
      column where the last six items of each tuple are :const:`None`.

      It is set for ``SELECT`` statements without any matching rows as well.

   .. attribute:: connection

      This read-only attribute provides the SQLite database :class:`Connection`
      used by the :class:`Cursor` object.  A :class:`Cursor` object created by
      calling :meth:`con.cursor() <Connection.cursor>` will have a
      :attr:`connection` attribute that refers to *con*::

         >>> con = sqlite3.connect(":memory:")
         >>> cur = con.cursor()
         >>> cur.connection == con
         True

.. _sqlite3-row-objects:

Row Objects
-----------

.. class:: Row

   A :class:`Row` instance serves as a highly optimized
   :attr:`~Connection.row_factory` for :class:`Connection` objects.
   It tries to mimic a tuple in most of its features.

   It supports mapping access by column name and index, iteration,
   representation, equality testing and :func:`len`.

   If two :class:`Row` objects have exactly the same columns and their
   members are equal, they compare equal.

   .. method:: keys

      This method returns a list of column names. Immediately after a query,
      it is the first member of each tuple in :attr:`Cursor.description`.

   .. versionchanged:: 3.5
      Added support of slicing.

Let's assume we initialize a table as in the example given above::

   conn = sqlite3.connect(":memory:")
   c = conn.cursor()
   c.execute('''create table stocks
   (date text, trans text, symbol text,
    qty real, price real)''')
   c.execute("""insert into stocks
             values ('2006-01-05','BUY','RHAT',100,35.14)""")
   conn.commit()
   c.close()

Now we plug :class:`Row` in::

   >>> conn.row_factory = sqlite3.Row
   >>> c = conn.cursor()
   >>> c.execute('select * from stocks')
   <sqlite3.Cursor object at 0x7f4e7dd8fa80>
   >>> r = c.fetchone()
   >>> type(r)
   <class 'sqlite3.Row'>
   >>> tuple(r)
   ('2006-01-05', 'BUY', 'RHAT', 100.0, 35.14)
   >>> len(r)
   5
   >>> r[2]
   'RHAT'
   >>> r.keys()
   ['date', 'trans', 'symbol', 'qty', 'price']
   >>> r['qty']
   100.0
   >>> for member in r:
   ...     print(member)
   ...
   2006-01-05
   BUY
   RHAT
   100.0
   35.14


.. _sqlite3-types:

SQLite and Python types
-----------------------


Introduction
^^^^^^^^^^^^

SQLite natively supports the following types: ``NULL``, ``INTEGER``,
``REAL``, ``TEXT``, ``BLOB``.

The following Python types can thus be sent to SQLite without any problem:

+-------------------------------+-------------+
| Python type                   | SQLite type |
+===============================+=============+
| :const:`None`                 | ``NULL``    |
+-------------------------------+-------------+
| :class:`int`                  | ``INTEGER`` |
+-------------------------------+-------------+
| :class:`float`                | ``REAL``    |
+-------------------------------+-------------+
| :class:`str`                  | ``TEXT``    |
+-------------------------------+-------------+
| :class:`bytes`                | ``BLOB``    |
+-------------------------------+-------------+


This is how SQLite types are converted to Python types by default:

+-------------+----------------------------------------------+
| SQLite type | Python type                                  |
+=============+==============================================+
| ``NULL``    | :const:`None`                                |
+-------------+----------------------------------------------+
| ``INTEGER`` | :class:`int`                                 |
+-------------+----------------------------------------------+
| ``REAL``    | :class:`float`                               |
+-------------+----------------------------------------------+
| ``TEXT``    | depends on :attr:`~Connection.text_factory`, |
|             | :class:`str` by default                      |
+-------------+----------------------------------------------+
| ``BLOB``    | :class:`bytes`                               |
+-------------+----------------------------------------------+

The type system of the :mod:`sqlite3` module is extensible in two ways: you can
store additional Python types in a SQLite database via object adaptation, and
you can let the :mod:`sqlite3` module convert SQLite types to different Python
types via converters.


Using adapters to store additional Python types in SQLite databases
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

As described before, SQLite supports only a limited set of types natively. To
use other Python types with SQLite, you must **adapt** them to one of the
sqlite3 module's supported types for SQLite: one of NoneType, int, float,
str, bytes.

There are two ways to enable the :mod:`sqlite3` module to adapt a custom Python
type to one of the supported ones.


Letting your object adapt itself
""""""""""""""""""""""""""""""""

This is a good approach if you write the class yourself. Let's suppose you have
a class like this::

   class Point:
       def __init__(self, x, y):
           self.x, self.y = x, y

Now you want to store the point in a single SQLite column.  First you'll have to
choose one of the supported types first to be used for representing the point.
Let's just use str and separate the coordinates using a semicolon. Then you need
to give your class a method ``__conform__(self, protocol)`` which must return
the converted value. The parameter *protocol* will be :class:`PrepareProtocol`.

.. literalinclude:: ../includes/sqlite3/adapter_point_1.py


Registering an adapter callable
"""""""""""""""""""""""""""""""

The other possibility is to create a function that converts the type to the
string representation and register the function with :meth:`register_adapter`.

.. literalinclude:: ../includes/sqlite3/adapter_point_2.py

The :mod:`sqlite3` module has two default adapters for Python's built-in
:class:`datetime.date` and :class:`datetime.datetime` types.  Now let's suppose
we want to store :class:`datetime.datetime` objects not in ISO representation,
but as a Unix timestamp.

.. literalinclude:: ../includes/sqlite3/adapter_datetime.py


Converting SQLite values to custom Python types
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Writing an adapter lets you send custom Python types to SQLite. But to make it
really useful we need to make the Python to SQLite to Python roundtrip work.

Enter converters.

Let's go back to the :class:`Point` class. We stored the x and y coordinates
separated via semicolons as strings in SQLite.

First, we'll define a converter function that accepts the string as a parameter
and constructs a :class:`Point` object from it.

.. note::

   Converter functions **always** get called with a :class:`bytes` object, no
   matter under which data type you sent the value to SQLite.

::

   def convert_point(s):
       x, y = map(float, s.split(b";"))
       return Point(x, y)

Now you need to make the :mod:`sqlite3` module know that what you select from
the database is actually a point. There are two ways of doing this:

* Implicitly via the declared type

* Explicitly via the column name

Both ways are described in section :ref:`sqlite3-module-contents`, in the entries
for the constants :const:`PARSE_DECLTYPES` and :const:`PARSE_COLNAMES`.

The following example illustrates both approaches.

.. literalinclude:: ../includes/sqlite3/converter_point.py


Default adapters and converters
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

There are default adapters for the date and datetime types in the datetime
module. They will be sent as ISO dates/ISO timestamps to SQLite.

The default converters are registered under the name "date" for
:class:`datetime.date` and under the name "timestamp" for
:class:`datetime.datetime`.

This way, you can use date/timestamps from Python without any additional
fiddling in most cases. The format of the adapters is also compatible with the
experimental SQLite date/time functions.

The following example demonstrates this.

.. literalinclude:: ../includes/sqlite3/pysqlite_datetime.py

If a timestamp stored in SQLite has a fractional part longer than 6
numbers, its value will be truncated to microsecond precision by the
timestamp converter.


.. _sqlite3-controlling-transactions:

Controlling Transactions
------------------------

By default, the :mod:`sqlite3` module opens transactions implicitly before a
Data Modification Language (DML)  statement (i.e.
``INSERT``/``UPDATE``/``DELETE``/``REPLACE``), and commits transactions
implicitly before a non-DML, non-query statement (i. e.
anything other than ``SELECT`` or the aforementioned).

So if you are within a transaction and issue a command like ``CREATE TABLE
...``, ``VACUUM``, ``PRAGMA``, the :mod:`sqlite3` module will commit implicitly
before executing that command. There are two reasons for doing that. The first
is that some of these commands don't work within transactions. The other reason
is that sqlite3 needs to keep track of the transaction state (if a transaction
is active or not).  The current transaction state is exposed through the
:attr:`Connection.in_transaction` attribute of the connection object.

You can control which kind of ``BEGIN`` statements sqlite3 implicitly executes
(or none at all) via the *isolation_level* parameter to the :func:`connect`
call, or via the :attr:`isolation_level` property of connections.

If you want **autocommit mode**, then set :attr:`isolation_level` to None.

Otherwise leave it at its default, which will result in a plain "BEGIN"
statement, or set it to one of SQLite's supported isolation levels: "DEFERRED",
"IMMEDIATE" or "EXCLUSIVE".



Using :mod:`sqlite3` efficiently
--------------------------------


Using shortcut methods
^^^^^^^^^^^^^^^^^^^^^^

Using the nonstandard :meth:`execute`, :meth:`executemany` and
:meth:`executescript` methods of the :class:`Connection` object, your code can
be written more concisely because you don't have to create the (often
superfluous) :class:`Cursor` objects explicitly. Instead, the :class:`Cursor`
objects are created implicitly and these shortcut methods return the cursor
objects. This way, you can execute a ``SELECT`` statement and iterate over it
directly using only a single call on the :class:`Connection` object.

.. literalinclude:: ../includes/sqlite3/shortcut_methods.py


Accessing columns by name instead of by index
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

One useful feature of the :mod:`sqlite3` module is the built-in
:class:`sqlite3.Row` class designed to be used as a row factory.

Rows wrapped with this class can be accessed both by index (like tuples) and
case-insensitively by name:

.. literalinclude:: ../includes/sqlite3/rowclass.py


Using the connection as a context manager
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Connection objects can be used as context managers
that automatically commit or rollback transactions.  In the event of an
exception, the transaction is rolled back; otherwise, the transaction is
committed:

.. literalinclude:: ../includes/sqlite3/ctx_manager.py


Common issues
-------------

Multithreading
^^^^^^^^^^^^^^

Older SQLite versions had issues with sharing connections between threads.
That's why the Python module disallows sharing connections and cursors between
threads. If you still try to do so, you will get an exception at runtime.

The only exception is calling the :meth:`~Connection.interrupt` method, which
only makes sense to call from a different thread.

.. rubric:: Footnotes

.. [#f1] The sqlite3 module is not built with loadable extension support by
   default, because some platforms (notably Mac OS X) have SQLite
   libraries which are compiled without this feature. To get loadable
   extension support, you must pass --enable-loadable-sqlite-extensions to
   configure.