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diff --git a/doc/sphinx/sqlcipher.rst b/doc/sphinx/sqlcipher.rst new file mode 100644 index 0000000..7785aeb --- /dev/null +++ b/doc/sphinx/sqlcipher.rst @@ -0,0 +1,887 @@ +:mod:`sqlcipher` --- DB-API 2.0 interface for SQCipher databases +============================================================== + +.. module:: sqlcipher + :synopsis: A DB-API 2.0 implementation using SQCipher 3.x. +.. sectionauthor:: Gerhard Häring <gh@ghaering.de> +.. sectionauthor:: Kali Kaneko <kali@leap.se> + +.. note:: This documentation has to be adapted to the use of SQLCipher + +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:: + + +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, 35.14) + (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://code.google.com/p/pysqlite/ + The pysqlite web page -- sqlite3 is developed externally under the name + "pysqlite". + + 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 "EXCLUSIVE". 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<Cursor.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<Cursor.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<Cursor.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) + + 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:: Connection.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. + + .. literalinclude:: ../includes/sqlite3/load_extension.py + +.. method:: Connection.load_extension(path) + + This routine loads a SQLite extension from a shared library. You have to + enable extension loading with ``enable_load_extension`` before you can use + this routine. + +.. 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. + + Example:: + + # Convert file existing_db.db to SQL dump file dump.sql + import sqlite3, os + + con = sqlite3.connect('existing_db.db') + full_dump = os.linesep.join([line for line in con.iterdump()]) + f = open('dump.sql', 'w') + f.writelines(full_dump) + f.close() + + +.. _sqlite3-cursor-objects: + +Cursor Objects +-------------- + +A :class:`Cursor` instance has the following attributes and methods: + + 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`. + + 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. + +.. attribute:: Cursor.lastrowid + + This read-only attribute provides the rowid of the last modified row. It is + only set if you issued a ``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:: Cursor.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. + +.. _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. + + .. versionchanged:: 2.6 + Added iteration and equality (hashability). + + .. method:: keys + + This method returns a tuple of column names. Immediately after a query, + it is the first member of each tuple in :attr:`Cursor.description`. + + .. versionadded:: 2.6 + +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) + <type 'sqlite3.Row'> + >>> r + (u'2006-01-05', u'BUY', u'RHAT', 100.0, 35.14) + >>> len(r) + 5 + >>> r[2] + u'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:`long` | ``INTEGER`` | ++-----------------------------+-------------+ +| :class:`float` | ``REAL`` | ++-----------------------------+-------------+ +| :class:`str` (UTF8-encoded) | ``TEXT`` | ++-----------------------------+-------------+ +| :class:`unicode` | ``TEXT`` | ++-----------------------------+-------------+ +| :class:`buffer` | ``BLOB`` | ++-----------------------------+-------------+ + +This is how SQLite types are converted to Python types by default: + ++-------------+----------------------------------------------+ +| SQLite type | Python type | ++=============+==============================================+ +| ``NULL`` | :const:`None` | ++-------------+----------------------------------------------+ +| ``INTEGER`` | :class:`int` or :class:`long`, | +| | depending on size | ++-------------+----------------------------------------------+ +| ``REAL`` | :class:`float` | ++-------------+----------------------------------------------+ +| ``TEXT`` | depends on :attr:`~Connection.text_factory`, | +| | :class:`unicode` by default | ++-------------+----------------------------------------------+ +| ``BLOB`` | :class:`buffer` | ++-------------+----------------------------------------------+ + +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, long, float, +str, unicode, buffer. + +The :mod:`sqlite3` module uses Python object adaptation, as described in +:pep:`246` for this. The protocol to use is :class:`PrepareProtocol`. + +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(object): + 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`. + +.. note:: + + The type/class to adapt must be a :term:`new-style class`, i. e. it must have + :class:`object` as one of its bases. + +.. 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 string, no matter under which + data type you sent the value to SQLite. + +:: + + def convert_point(s): + x, y = map(float, s.split(";")) + 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 + + +.. _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 pysqlite needs to keep track of the transaction state (if a transaction +is active or not). + +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 +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +With Python 2.5 or higher, 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. + |