: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 an SQL interface compliant with the DB-API 2.0 specification described by PEP 249, and requires SQLite 3.7.15 or newer.
To use the module, start by creating a :class:`Connection` object that represents the database. Here the data will be stored in the :file:`example.db` file:
import sqlite3
con = sqlite3.connect('example.db')
The special path name :memory: can be provided to create a temporary
database in RAM.
Once a :class:`Connection` has been established, create a :class:`Cursor` object and call its :meth:`~Cursor.execute` method to perform SQL commands:
cur = con.cursor()
# Create table
cur.execute('''CREATE TABLE stocks
(date text, trans text, symbol text, qty real, price real)''')
# Insert a row of data
cur.execute("INSERT INTO stocks VALUES ('2006-01-05','BUY','RHAT',100,35.14)")
# Save (commit) the changes
con.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.
con.close()
The saved data is persistent: it can be reloaded in a subsequent session even after restarting the Python interpreter:
import sqlite3
con = sqlite3.connect('example.db')
cur = con.cursor()
To retrieve data after executing a SELECT statement, 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 cur.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)
SQL operations usually need to use values from Python variables. However, beware of using Python's string operations to assemble queries, as they are vulnerable to SQL injection attacks (see the xkcd webcomic for a humorous example of what can go wrong):
# Never do this -- insecure!
symbol = 'RHAT'
cur.execute("SELECT * FROM stocks WHERE symbol = '%s'" % symbol)
Instead, use the DB-API's parameter substitution. To insert a variable into a
query string, use a placeholder in the string, and substitute the actual values
into the query by providing them as a :class:`tuple` of values to the second
argument of the cursor's :meth:`~Cursor.execute` method. An SQL statement may
use one of two kinds of placeholders: question marks (qmark style) or named
placeholders (named style). For the qmark style, parameters must be a
:term:`sequence <sequence>`. For the named style, it can be either a
:term:`sequence <sequence>` or :class:`dict` instance. The length of the
:term:`sequence <sequence>` must match the number of placeholders, or a
:exc:`ProgrammingError` is raised. If a :class:`dict` is given, it must contain
keys for all named parameters. Any extra items are ignored. Here's an example of
both styles:
.. literalinclude:: ../includes/sqlite3/execute_1.py
.. seealso::
https://www.sqlite.org
The SQLite web page; the documentation describes the syntax and the
available data types for the supported SQL dialect.
https://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.
.. data:: apilevel String constant stating the supported DB-API level. Required by the DB-API. Hard-coded to ``"2.0"``.
.. data:: paramstyle
String constant stating the type of parameter marker formatting expected by
the :mod:`sqlite3` module. Required by the DB-API. Hard-coded to
``"qmark"``.
.. note::
The :mod:`sqlite3` module supports both ``qmark`` and ``numeric`` DB-API
parameter styles, because that is what the underlying SQLite library
supports. However, the DB-API does not allow multiple values for
the ``paramstyle`` attribute.
.. 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:: threadsafety
Integer constant required by the DB-API 2.0, stating the level of thread
safety the :mod:`sqlite3` module supports. This attribute is set based on
the default `threading mode <https://sqlite.org/threadsafe.html>`_ the
underlying SQLite library is compiled with. The SQLite threading modes are:
1. **Single-thread**: In this mode, all mutexes are disabled and SQLite is
unsafe to use in more than a single thread at once.
2. **Multi-thread**: In this mode, SQLite can be safely used by multiple
threads provided that no single database connection is used
simultaneously in two or more threads.
3. **Serialized**: In serialized mode, SQLite can be safely used by
multiple threads with no restriction.
The mappings from SQLite threading modes to DB-API 2.0 threadsafety levels
are as follows:
+------------------+-----------------+----------------------+-------------------------------+
| SQLite threading | `threadsafety`_ | `SQLITE_THREADSAFE`_ | DB-API 2.0 meaning |
| mode | | | |
+==================+=================+======================+===============================+
| single-thread | 0 | 0 | Threads may not share the |
| | | | module |
+------------------+-----------------+----------------------+-------------------------------+
| multi-thread | 1 | 2 | Threads may share the module, |
| | | | but not connections |
+------------------+-----------------+----------------------+-------------------------------+
| serialized | 3 | 1 | Threads may share the module, |
| | | | connections and cursors |
+------------------+-----------------+----------------------+-------------------------------+
.. _threadsafety: https://peps.python.org/pep-0249/#threadsafety
.. _SQLITE_THREADSAFE: https://sqlite.org/compile.html#threadsafe
.. versionchanged:: 3.11
Set *threadsafety* dynamically instead of hard-coding it to ``1``.
.. 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` does not include the type, i. e. if you use something like ``'as "Expiration date [datetime]"'`` in your SQL, then we will parse out everything until the first ``'['`` for the column name and strip the preceding space: the column name would simply be "Expiration date".
.. function:: connect(database[, timeout, detect_types, isolation_level, check_same_thread, factory, cached_statements, uri])
Opens a connection to the SQLite database file *database*. By default returns a
:class:`Connection` object, unless a custom *factory* is given.
*database* is a :term:`path-like object` giving the pathname (absolute or
relative to the current working directory) of the database file to be opened.
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. Due to SQLite behaviour, types can't be detected for generated
fields (for example ``max(data)``), even when *detect_types* parameter is set. In
such case, the returned type is :class:`str`.
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 128 statements.
If *uri* is :const:`True`, *database* is interpreted as a
:abbr:`URI (Uniform Resource Identifier)` with a file path and an optional
query string. The scheme part *must* be ``"file:"``. The path can be a
relative or absolute file path. The query string allows us to pass
parameters to SQLite. Some useful URI tricks include::
# Open a database in read-only mode.
con = sqlite3.connect("file:template.db?mode=ro", uri=True)
# Don't implicitly create a new database file if it does not already exist.
# Will raise sqlite3.OperationalError if unable to open a database file.
con = sqlite3.connect("file:nosuchdb.db?mode=rw", uri=True)
# Create a shared named in-memory database.
con1 = sqlite3.connect("file:mem1?mode=memory&cache=shared", uri=True)
con2 = sqlite3.connect("file:mem1?mode=memory&cache=shared", uri=True)
con1.executescript("create table t(t); insert into t values(28);")
rows = con2.execute("select * from t").fetchall()
More information about this feature, including a list of recognized
parameters, can be found in the
`SQLite URI documentation <https://www.sqlite.org/uri.html>`_.
.. audit-event:: sqlite3.connect database sqlite3.connect
.. audit-event:: sqlite3.connect/handle connection_handle sqlite3.connect
.. versionchanged:: 3.4
Added the *uri* parameter.
.. versionchanged:: 3.7
*database* can now also be a :term:`path-like object`, not only a string.
.. versionchanged:: 3.10
Added the ``sqlite3.connect/handle`` auditing event.
.. 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 *typename* and the name of the type in your query are matched in case-insensitive manner.
.. 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(statement) Returns :const:`True` if the string *statement* 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 :const:`True`. Afterwards, you
will get tracebacks from callbacks on :data:`sys.stderr`. Use :const:`False`
to disable the feature again.
Register an :func:`unraisable hook handler <sys.unraisablehook>` for an
improved debug experience::
>>> import sqlite3
>>> sqlite3.enable_callback_tracebacks(True)
>>> cx = sqlite3.connect(":memory:")
>>> cx.set_trace_callback(lambda stmt: 5/0)
>>> cx.execute("select 1")
Exception ignored in: <function <lambda> at 0x10b4e3ee0>
Traceback (most recent call last):
File "<stdin>", line 1, in <lambda>
ZeroDivisionError: division by zero
>>> import sys
>>> sys.unraisablehook = lambda unraisable: print(unraisable)
>>> cx.execute("select 1")
UnraisableHookArgs(exc_type=<class 'ZeroDivisionError'>, exc_value=ZeroDivisionError('division by zero'), exc_traceback=<traceback object at 0x10b559900>, err_msg=None, object=<function <lambda> at 0x10b4e3ee0>)
<sqlite3.Cursor object at 0x10b1fe840>
An SQLite database connection has the following attributes and methods:
.. attribute:: isolation_level Get or set the current default 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(factory=Cursor) The cursor method accepts a single optional parameter *factory*. If supplied, this must be a callable returning an instance of :class:`Cursor` or its subclasses.
.. method:: blobopen(table, column, row, /, *, readonly=False, name="main")
Open a :class:`Blob` handle to the :abbr:`BLOB (Binary Large OBject)`
located in table name *table*, column name *column*, and row index *row*
of database *name*.
When *readonly* is :const:`True` the blob is opened without write
permissions.
Trying to open a blob in a ``WITHOUT ROWID`` table will raise
:exc:`OperationalError`.
.. note::
The blob size cannot be changed using the :class:`Blob` class.
Use the SQL function ``zeroblob`` to create a blob with a fixed size.
.. versionadded:: 3.11
.. method:: commit() Commit any pending transaction to the database. If there is no open transaction, this method is a no-op.
.. method:: rollback() Roll back to the start of any pending transaction. If there is no open transaction, this method is a no-op.
.. method:: close() Close the database connection. Any pending transaction is not committed implicitly; make sure to :meth:`commit` before closing to avoid losing pending changes.
.. method:: execute(sql[, parameters]) Create a new :class:`Cursor` object and call :meth:`~Cursor.execute` on it with the given *sql* and *parameters*. Return the new cursor object.
.. method:: executemany(sql[, parameters]) Create a new :class:`Cursor` object and call :meth:`~Cursor.executemany` on it with the given *sql* and *parameters*. Return the new cursor object.
.. method:: executescript(sql_script) Create a new :class:`Cursor` object and call :meth:`~Cursor.executescript` on it with the given *sql_script*. Return the new cursor object.
.. method:: create_function(name, narg, func, *, deterministic=False)
Creates a user-defined function that you can later use from within SQL
statements under the function name *name*. *narg* is the number of
parameters the function accepts (if *narg* is -1, the function may
take any number of arguments), and *func* is a Python callable that is
called as the SQL function. If *deterministic* is true, the created function
is marked as `deterministic <https://sqlite.org/deterministic.html>`_, which
allows SQLite to perform additional optimizations. This flag is supported by
SQLite 3.8.3 or higher, :exc:`NotSupportedError` will be raised if used
with older versions.
The function can return any of the types supported by SQLite: bytes, str, int,
float and ``None``.
.. versionchanged:: 3.8
The *deterministic* parameter was added.
Example:
.. literalinclude:: ../includes/sqlite3/md5func.py
.. method:: create_aggregate(name, n_arg, aggregate_class) Creates a user-defined aggregate function. The aggregate class must implement a ``step`` method, which accepts the number of parameters *n_arg* (if *n_arg* 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_window_function(name, num_params, aggregate_class, /) Creates user-defined aggregate window function *name*. *aggregate_class* must implement the following methods: * ``step``: adds a row to the current window * ``value``: returns the current value of the aggregate * ``inverse``: removes a row from the current window * ``finalize``: returns the final value of the aggregate ``step`` and ``value`` accept *num_params* number of parameters, unless *num_params* is ``-1``, in which case they may take any number of arguments. ``finalize`` and ``value`` can return any of the types supported by SQLite: :class:`bytes`, :class:`str`, :class:`int`, :class:`float`, and :const:`None`. Call :meth:`create_window_function` with *aggregate_class* set to :const:`None` to clear window function *name*. Aggregate window functions are supported by SQLite 3.25.0 and higher. :exc:`NotSupportedError` will be raised if used with older versions. .. versionadded:: 3.11 Example: .. literalinclude:: ../includes/sqlite3/sumintwindow.py
.. method:: create_collation(name, callable)
Create a collation named *name* using the collating function *callable*.
*callable* is passed two :class:`string <str>` arguments,
and it should return an :class:`integer <int>`:
* ``1`` if the first is ordered higher than the second
* ``-1`` if the first is ordered lower than the second
* ``0`` if they are ordered equal
The following example shows a reverse sorting collation:
.. literalinclude:: ../includes/sqlite3/collation_reverse.py
Remove a collation function by setting *callable* to :const:`None`.
.. versionchanged:: 3.11
The collation name can contain any Unicode character. Earlier, only
ASCII characters were allowed.
.. 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.
Passing :const:`None` as *authorizer_callback* will disable the authorizer.
.. versionchanged:: 3.11
Added support for disabling the authorizer using :const:`None`.
.. method:: set_progress_handler(progress_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 *progress_handler*. Returning a non-zero value from the handler function will terminate the currently executing query and cause it to raise an :exc:`OperationalError` exception.
.. 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
:class:`str`) 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
:ref:`transaction management <sqlite3-controlling-transactions>` of the
sqlite3 module and the execution of triggers defined in the current
database.
Passing :const:`None` as *trace_callback* will disable the trace callback.
.. note::
Exceptions raised in the trace callback are not propagated. As a
development and debugging aid, use
:meth:`~sqlite3.enable_callback_tracebacks` to enable printing
tracebacks from exceptions raised in 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]_.
.. audit-event:: sqlite3.enable_load_extension connection,enabled sqlite3.Connection.enable_load_extension
.. versionadded:: 3.2
.. versionchanged:: 3.10
Added the ``sqlite3.enable_load_extension`` auditing event.
.. literalinclude:: ../includes/sqlite3/load_extension.py
.. method:: load_extension(path)
This routine loads an 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]_.
.. audit-event:: sqlite3.load_extension connection,path sqlite3.Connection.load_extension
.. versionadded:: 3.2
.. versionchanged:: 3.10
Added the ``sqlite3.load_extension`` auditing event.
.. 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 :class:`str` objects for ``TEXT``. If you want to return :class:`bytes` 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)
con.close()
.. method:: backup(target, *, pages=-1, progress=None, name="main", sleep=0.250)
This method makes a backup of an SQLite database even while it's being accessed
by other clients, or concurrently by the same connection. The copy will be
written into the mandatory argument *target*, that must be another
:class:`Connection` instance.
By default, or when *pages* is either ``0`` or a negative integer, the entire
database is copied in a single step; otherwise the method performs a loop
copying up to *pages* pages at a time.
If *progress* is specified, it must either be ``None`` or a callable object that
will be executed at each iteration with three integer arguments, respectively
the *status* of the last iteration, the *remaining* number of pages still to be
copied and the *total* number of pages.
The *name* argument specifies the database name that will be copied: it must be
a string containing either ``"main"``, the default, to indicate the main
database, ``"temp"`` to indicate the temporary database or the name specified
after the ``AS`` keyword in an ``ATTACH DATABASE`` statement for an attached
database.
The *sleep* argument specifies the number of seconds to sleep by between
successive attempts to backup remaining pages, can be specified either as an
integer or a floating point value.
Example 1, copy an existing database into another::
import sqlite3
def progress(status, remaining, total):
print(f'Copied {total-remaining} of {total} pages...')
con = sqlite3.connect('existing_db.db')
bck = sqlite3.connect('backup.db')
with bck:
con.backup(bck, pages=1, progress=progress)
bck.close()
con.close()
Example 2, copy an existing database into a transient copy::
import sqlite3
source = sqlite3.connect('existing_db.db')
dest = sqlite3.connect(':memory:')
source.backup(dest)
.. versionadded:: 3.7
.. method:: getlimit(category, /)
Get a connection run-time limit. *category* is the limit category to be
queried.
Example, query the maximum length of an SQL statement::
import sqlite3
con = sqlite3.connect(":memory:")
lim = con.getlimit(sqlite3.SQLITE_LIMIT_SQL_LENGTH)
print(f"SQLITE_LIMIT_SQL_LENGTH={lim}")
.. versionadded:: 3.11
.. method:: setlimit(category, limit, /)
Set a connection run-time limit. *category* is the limit category to be
set. *limit* is the new limit. If the new limit is a negative number, the
limit is unchanged.
Attempts to increase a limit above its hard upper bound are silently
truncated to the hard upper bound. Regardless of whether or not the limit
was changed, the prior value of the limit is returned.
Example, limit the number of attached databases to 1::
import sqlite3
con = sqlite3.connect(":memory:")
con.setlimit(sqlite3.SQLITE_LIMIT_ATTACHED, 1)
.. versionadded:: 3.11
.. method:: serialize(*, name="main")
This method serializes a database into a :class:`bytes` object. For an
ordinary on-disk database file, the serialization is just a copy of the
disk file. For an in-memory database or a "temp" database, the
serialization is the same sequence of bytes which would be written to
disk if that database were backed up to disk.
*name* is the database to be serialized, and defaults to the main
database.
.. note::
This method is only available if the underlying SQLite library has the
serialize API.
.. versionadded:: 3.11
.. method:: deserialize(data, /, *, name="main")
This method causes the database connection to disconnect from database
*name*, and reopen *name* as an in-memory database based on the
serialization contained in *data*. Deserialization will raise
:exc:`OperationalError` if the database connection is currently involved
in a read transaction or a backup operation. :exc:`OverflowError` will be
raised if ``len(data)`` is larger than ``2**63 - 1``, and
:exc:`DatabaseError` will be raised if *data* does not contain a valid
SQLite database.
.. note::
This method is only available if the underlying SQLite library has the
deserialize API.
.. versionadded:: 3.11
A :class:`Cursor` instance has the following attributes and methods.
.. index:: single: ? (question mark); in SQL statements
.. index:: single: : (colon); in SQL statements
.. method:: execute(sql[, parameters]) Executes an SQL statement. Values may be bound to the statement using :ref:`placeholders <sqlite3-placeholders>`. :meth:`execute` will only execute a single SQL statement. If you try to execute more than one statement with it, it will raise a :exc:`ProgrammingError`. Use :meth:`executescript` if you want to execute multiple SQL statements with one call.
.. method:: executemany(sql, seq_of_parameters) Executes a :ref:`parameterized <sqlite3-placeholders>` 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. This method disregards :attr:`isolation_level`; any transaction control must be added to *sql_script*. *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 :exc:`ProgrammingError` exception will be raised if any operation is attempted with the cursor.
.. method:: setinputsizes(sizes) Required by the DB-API. Does nothing in :mod:`sqlite3`.
.. method:: setoutputsize(size [, column]) Required by the DB-API. Does nothing in :mod:`sqlite3`.
.. 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.
.. attribute:: lastrowid
This read-only attribute provides the row id of the last inserted row. It
is only updated after successful ``INSERT`` or ``REPLACE`` statements
using the :meth:`execute` method. For other statements, after
:meth:`executemany` or :meth:`executescript`, or if the insertion failed,
the value of ``lastrowid`` is left unchanged. The initial value of
``lastrowid`` is :const:`None`.
.. note::
Inserts into ``WITHOUT ROWID`` tables are not recorded.
.. versionchanged:: 3.6
Added support for the ``REPLACE`` statement.
.. attribute:: arraysize Read/write attribute that controls the number of rows returned by :meth:`fetchmany`. The default value is 1 which means a single row would be fetched per call.
.. 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
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:
con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.execute('''create table stocks
(date text, trans text, symbol text,
qty real, price real)''')
cur.execute("""insert into stocks
values ('2006-01-05','BUY','RHAT',100,35.14)""")
con.commit()
cur.close()
Now we plug :class:`Row` in:
>>> con.row_factory = sqlite3.Row
>>> cur = con.cursor()
>>> cur.execute('select * from stocks')
<sqlite3.Cursor object at 0x7f4e7dd8fa80>
>>> r = cur.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
.. versionadded:: 3.11
A :class:`Blob` instance is a :term:`file-like object` that can read and write data in an SQLite :abbr:`BLOB (Binary Large OBject)`. Call :func:`len(blob) <len>` to get the size (number of bytes) of the blob. Use indices and :term:`slices <slice>` for direct access to the blob data.
Use the :class:`Blob` as a :term:`context manager` to ensure that the blob handle is closed after use.
.. literalinclude:: ../includes/sqlite3/blob.py
.. method:: close() Close the blob. The blob will be unusable from this point onward. An :class:`~sqlite3.Error` (or subclass) exception will be raised if any further operation is attempted with the blob.
.. method:: read(length=-1, /) Read *length* bytes of data from the blob at the current offset position. If the end of the blob is reached, the data up to :abbr:`EOF (End of File)` will be returned. When *length* is not specified, or is negative, :meth:`~Blob.read` will read until the end of the blob.
.. method:: write(data, /) Write *data* to the blob at the current offset. This function cannot change the blob length. Writing beyond the end of the blob will raise :exc:`ValueError`.
.. method:: tell() Return the current access position of the blob.
.. method:: seek(offset, origin=os.SEEK_SET, /) Set the current access position of the blob to *offset*. The *origin* argument defaults to :data:`os.SEEK_SET` (absolute blob positioning). Other values for *origin* are :data:`os.SEEK_CUR` (seek relative to the current position) and :data:`os.SEEK_END` (seek relative to the blob’s end).
The exception hierarchy is defined by the DB-API 2.0 (PEP 249).
.. exception:: Warning This exception is not currently raised by the ``sqlite3`` module, but may be raised by applications using ``sqlite3``, for example if a user-defined function truncates data while inserting. ``Warning`` is a subclass of :exc:`Exception`.
.. exception:: Error
The base class of the other exceptions in this module.
Use this to catch all errors with one single :keyword:`except` statement.
``Error`` is a subclass of :exc:`Exception`.
.. attribute:: sqlite_errorcode
The numeric error code from the
`SQLite API <https://sqlite.org/rescode.html>`_
.. versionadded:: 3.11
.. attribute:: sqlite_errorname
The symbolic name of the numeric error code
from the `SQLite API <https://sqlite.org/rescode.html>`_
.. versionadded:: 3.11
.. exception:: InterfaceError Exception raised for misuse of the low-level SQLite C API. In other words, if this exception is raised, it probably indicates a bug in the ``sqlite3`` module. ``InterfaceError`` is a subclass of :exc:`Error`.
.. exception:: DatabaseError Exception raised for errors that are related to the database. This serves as the base exception for several types of database errors. It is only raised implicitly through the specialised subclasses. ``DatabaseError`` is a subclass of :exc:`Error`.
.. exception:: DataError Exception raised for errors caused by problems with the processed data, like numeric values out of range, and strings which are too long. ``DataError`` is a subclass of :exc:`DatabaseError`.
.. exception:: OperationalError Exception raised for errors that are related to the database's operation, and not necessarily under the control of the programmer. For example, the database path is not found, or a transaction could not be processed. ``OperationalError`` is a subclass of :exc:`DatabaseError`.
.. exception:: IntegrityError Exception raised when the relational integrity of the database is affected, e.g. a foreign key check fails. It is a subclass of :exc:`DatabaseError`.
.. exception:: InternalError Exception raised when SQLite encounters an internal error. If this is raised, it may indicate that there is a problem with the runtime SQLite library. ``InternalError`` is a subclass of :exc:`DatabaseError`.
.. exception:: ProgrammingError Exception raised for ``sqlite3`` API programming errors, for example supplying the wrong number of bindings to a query, or trying to operate on a closed :class:`Connection`. ``ProgrammingError`` is a subclass of :exc:`DatabaseError`.
.. exception:: NotSupportedError Exception raised in case a method or database API is not supported by the underlying SQLite library. For example, setting *deterministic* to :const:`True` in :meth:`~Connection.create_function`, if the underlying SQLite library does not support deterministic functions. ``NotSupportedError`` is a subclass of :exc:`DatabaseError`.
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 an SQLite database via object adaptation, and you can let the :mod:`sqlite3` module convert SQLite types to different Python types via converters.
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.
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 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
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
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
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.
Note
The default "timestamp" converter ignores UTC offsets in the database and always returns a naive :class:`datetime.datetime` object. To preserve UTC offsets in timestamps, either leave converters disabled, or register an offset-aware converter with :func:`register_converter`.
The underlying sqlite3 library operates in autocommit mode by default,
but the Python :mod:`sqlite3` module by default does not.
autocommit mode means that statements that modify the database take effect
immediately. A BEGIN or SAVEPOINT statement disables autocommit
mode, and a COMMIT, a ROLLBACK, or a RELEASE that ends the
outermost transaction, turns autocommit mode back on.
The Python :mod:`sqlite3` module by default issues a BEGIN statement
implicitly before a Data Modification Language (DML) statement (i.e.
INSERT/UPDATE/DELETE/REPLACE).
You can control which kind of BEGIN statements :mod:`sqlite3` implicitly
executes via the isolation_level parameter to the :func:`connect`
call, or via the :attr:`isolation_level` property of connections.
If you specify no isolation_level, a plain BEGIN is used, which is
equivalent to specifying DEFERRED. Other possible values are IMMEDIATE
and EXCLUSIVE.
You can disable the :mod:`sqlite3` module's implicit transaction management by
setting :attr:`isolation_level` to None. This will leave the underlying
sqlite3 library operating in autocommit mode. You can then completely
control the transaction state by explicitly issuing BEGIN, ROLLBACK,
SAVEPOINT, and RELEASE statements in your code.
Note that :meth:`~Cursor.executescript` disregards :attr:`isolation_level`; any transaction control must be added explicitly.
.. versionchanged:: 3.6 :mod:`sqlite3` used to implicitly commit an open transaction before DDL statements. This is no longer the case.
Using :mod:`sqlite3` efficiently
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
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
A :class:`Connection` object can be used as a context manager that
automatically commits or rolls back open transactions when leaving the body of
the context manager.
If the body of the :keyword:`with` statement finishes without exceptions,
the transaction is committed.
If this commit fails,
or if the body of the with statement raises an uncaught exception,
the transaction is rolled back.
If there is no open transaction upon leaving the body of the with statement,
the context manager is a no-op.
Note
The context manager neither implicitly opens a new transaction nor closes the connection.
.. literalinclude:: ../includes/sqlite3/ctx_manager.py
Footnotes
| [1] | The sqlite3 module is not built with loadable extension support by default, because some platforms (notably macOS) have SQLite libraries which are compiled without this feature. To get loadable extension support, you must pass the :option:`--enable-loadable-sqlite-extensions` option to configure. |