: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>

.. versionadded:: 2.5

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.

pysqlite was written by Gerhard Häring and 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:`/tmp/example` file::

   conn = sqlite3.connect('/tmp/example')

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 cursor if we are done with it

   c.close()

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.

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 = 'IBM'

   c.execute("... where symbol = '%s'" % symbol)

   # Do this instead

   t = (symbol,)

   c.execute('select * from stocks where symbol=?', t)

   # Larger example

   for t in [('2006-03-28', 'BUY', 'IBM', 1000, 45.00),

             ('2006-04-05', 'BUY', 'MSOFT', 1000, 72.00),

             ('2006-04-06', 'SELL', 'IBM', 500, 53.00),

            ]:

       c.execute('insert into stocks values (?,?,?,?,?)', t)

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::

   >>> c = conn.cursor()

   >>> c.execute('select * from stocks order by price')

   >>> for row in c:

   ...    print row

   ...

   (u'2006-01-05', u'BUY', u'RHAT', 100, 35.140000000000001)

   (u'2006-03-28', u'BUY', u'IBM', 1000, 45.0)

   (u'2006-04-06', u'SELL', u'IBM', 500, 53.0)

   (u'2006-04-05', u'BUY', u'MSOFT', 1000, 72.0)

   >>>

.. seealso::

   http://www.pysqlite.org

      The pysqlite web page.

   http://www.sqlite.org

      The SQLite web page; the documentation describes the syntax and the available

      data types for the supported SQL dialect.

   :pep:`249` - Database API Specification 2.0

      PEP written by Marc-André Lemburg.

.. _sqlite3-module-contents:

Module functions and constants

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

.. 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, isolation_level, detect_types, factory])

   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, FLOAT, 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, 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.

.. 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, long,

   float, str (UTF-8 encoded), unicode or buffer.

.. 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* as 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:: Connection.isolation_level

   Get or set the current isolation level. :const:`None` for autocommit mode or one of

   "DEFERRED", "IMMEDIATE" or "EXLUSIVE". See section

   :ref:`sqlite3-controlling-transactions` for a more detailed explanation.

.. method:: Connection.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:: Connection.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 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:: Connection.rollback()

   This method rolls back any changes to the database since the last call to 

   :meth:`commit`.

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

   This is a nonstandard shortcut that creates an intermediate cursor object by

   calling the cursor method, then calls the cursor's :meth:`execute` method with

   the parameters given.

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

   This is a nonstandard shortcut that creates an intermediate cursor object by

   calling the cursor method, then calls the cursor's :meth:`executemany` method

   with the parameters given.

.. method:: Connection.executescript(sql_script)

   This is a nonstandard shortcut that creates an intermediate cursor object by

   calling the cursor method, then calls the cursor's :meth:`executescript` method

   with the parameters given.

.. method:: Connection.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, and *func* is a Python callable that is called

   as the SQL function.

   The function can return any of the types supported by SQLite: unicode, str, int,

   long, float, buffer and None.

   Example:

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

.. method:: Connection.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*, 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:

   unicode, str, int, long, float, buffer and None.

   Example:

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

.. method:: Connection.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:: Connection.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:: Connection.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:: Connection.set_progress_handler(handler, n)

   .. versionadded:: 2.6

   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*.

.. attribute:: Connection.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:: Connection.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:`unicode` and the

   :mod:`sqlite3` module will return Unicode objects for ``TEXT``. If you want to

   return bytestrings instead, you can set it to :class:`str`.

   For efficiency reasons, there's also a way to return Unicode objects only for

   non-ASCII data, and bytestrings otherwise. To activate it, set this attribute to

   :const:`sqlite3.OptimizedUnicode`.

   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:: Connection.total_changes

   Returns the total number of database rows that have been modified, inserted, or

   deleted since the database connection was opened.

.. attribute:: Connection.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.

   .. versionadded:: 2.6

   Example::

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

      import sqlite3, os

      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 SQLite database cursor has the following attributes and methods:

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

   Executes an SQL statement. The SQL statement may be parametrized (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).

   This example shows how to use parameters with qmark style:

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

   This example shows how to use the named style:

   .. literalinclude:: ../includes/sqlite3/execute_2.py

   :meth:`execute` will only execute a single SQL statement. If you try to execute

   more than one statement with it, it will raise a Warning. Use

   :meth:`executescript` if you want to execute multiple SQL statements with one

   call.

.. method:: Cursor.executemany(sql, seq_of_parameters)

   Executes an SQL command against all parameter sequences or mappings found in

   the sequence *sql*.  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:: Cursor.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 a bytestring or a Unicode string.

   Example:

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

.. method:: Cursor.fetchone() 

   Fetches the next row of a query result set, returning a single sequence,

   or :const:`None` when no more data is available.

.. method:: Cursor.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:: Cursor.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.

.. attribute:: Cursor.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 ``DELETE`` statements, SQLite reports :attr:`rowcount` as 0 if you make a

   ``DELETE FROM table`` without any condition.

   For :meth:`executemany` statements, the number of modifications are summed up

   into :attr:`rowcount`.