sqlite3
Gerhard Häring <gh@ghaering.de>
Source code: 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 249
, and requires SQLite 3.7.15 or newer.
To use the module, start by creating a Connection
object that represents the database. Here the data will be stored in the 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 Connection
has been established, create a Cursor
object and call its ~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 iterator
, call the cursor's ~Cursor.fetchone
method to retrieve a single matching row, or call ~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 tuple
of values to the second argument of the cursor's ~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 sequence <sequence>
. For the named style, it can be either a sequence <sequence>
or dict
instance. The length of the sequence <sequence>
must match the number of placeholders, or a ProgrammingError
is raised. If a dict
is given, it must contain keys for all named parameters. Any extra items are ignored. Here's an example of both styles:
../includes/sqlite3/execute_1.py
- 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.
249
- Database API Specification 2.0PEP written by Marc-André Lemburg.
apilevel
String constant stating the supported DB-API level. Required by the DB-API. Hard-coded to "2.0"
.
paramstyle
String constant stating the type of parameter marker formatting expected by the sqlite3
module. Required by the DB-API. Hard-coded to "qmark"
.
Note
The 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.
version
The version number of this module, as a string. This is not the version of the SQLite library.
version_info
The version number of this module, as a tuple of integers. This is not the version of the SQLite library.
sqlite_version
The version number of the run-time SQLite library, as a string.
sqlite_version_info
The version number of the run-time SQLite library, as a tuple of integers.
threadsafety
Integer constant required by the DB-API 2.0, stating the level of thread safety the sqlite3
module supports. This attribute is set based on the default threading mode the underlying SQLite library is compiled with. The SQLite threading modes are:
- Single-thread: In this mode, all mutexes are disabled and SQLite is unsafe to use in more than a single thread at once.
- 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.
- 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 mode | threadsafety | SQLITE_THREADSAFE | DB-API 2.0 meaning |
---|---|---|---|
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 |
3.11 Set threadsafety dynamically instead of hard-coding it to 1
.
PARSE_DECLTYPES
This constant is meant to be used with the detect_types parameter of the connect
function.
Setting it makes the 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.
PARSE_COLNAMES
This constant is meant to be used with the detect_types parameter of the 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 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".
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 Connection
object, unless a custom factory is given.
database is a 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 ~Connection.isolation_level
property of 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 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 PARSE_DECLTYPES
and 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 str
.
By default, check_same_thread is True
and only the creating thread may use the connection. If set 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 sqlite3
module uses its Connection
class for the connect call. You can, however, subclass the Connection
class and make connect
use your class instead by providing your class for the factory parameter.
Consult the section sqlite3-types
of this manual for details.
The 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 True
, database is interpreted as a 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.
sqlite3.connect database sqlite3.connect
sqlite3.connect/handle connection_handle sqlite3.connect
3.4 Added the uri parameter.
3.7 database can now also be a path-like object
, not only a string.
3.10 Added the sqlite3.connect/handle
auditing event.
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 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.
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.
complete_statement(sql)
Returns 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:
../includes/sqlite3/complete_statement.py
enable_callback_tracebacks(flag)
By default you will not get any tracebacks in user-defined functions, aggregates, converters, authorizer callbacks etc. If you want to debug them, you can call this function with flag set to True
. Afterwards, you will get tracebacks from callbacks on sys.stderr
. Use False
to disable the feature again.
Register an 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:
isolation_level
Get or set the current default isolation level. None
for autocommit mode or one of "DEFERRED", "IMMEDIATE" or "EXCLUSIVE". See section sqlite3-controlling-transactions
for a more detailed explanation.
in_transaction
True
if a transaction is active (there are uncommitted changes), False
otherwise. Read-only attribute.
3.2
cursor(factory=Cursor)
The cursor method accepts a single optional parameter factory. If supplied, this must be a callable returning an instance of Cursor
or its subclasses.
blobopen(table, column, row, /, *, readonly=False, name="main")
Open a Blob
handle to the BLOB (Binary Large OBject)
located in table name table, column name column, and row index row of database name. When readonly is True
the blob is opened without write permissions. Trying to open a blob in a WITHOUT ROWID
table will raise OperationalError
.
Note
The blob size cannot be changed using the Blob
class. Use the SQL function zeroblob
to create a blob with a fixed size.
3.11
commit()
This method commits the current transaction. If you don't call this method, anything you did since the last call to commit()
is not visible from other database connections. If you wonder why you don't see the data you've written to the database, please check you didn't forget to call this method.
rollback()
This method rolls back any changes to the database since the last call to commit
.
close()
This closes the database connection. Note that this does not automatically call commit
. If you just close your database connection without calling commit
first, your changes will be lost!
execute(sql[, parameters])
Create a new Cursor
object and call ~Cursor.execute
on it with the given sql and parameters. Return the new cursor object.
executemany(sql[, parameters])
Create a new Cursor
object and call ~Cursor.executemany
on it with the given sql and parameters. Return the new cursor object.
executescript(sql_script)
Create a new Cursor
object and call ~Cursor.executescript
on it with the given sql_script. Return the new cursor object.
create_function(name, num_params, func, *, deterministic=False)
Creates a user-defined function that you can later use from within SQL statements under the function name name. num_params is the number of parameters the function accepts (if num_params is -1, the function may take any number of arguments), and func is a Python callable that is called as the SQL function. If deterministic is true, the created function is marked as deterministic, which allows SQLite to perform additional optimizations. This flag is supported by SQLite 3.8.3 or higher, 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
.
3.8 The deterministic parameter was added.
Example:
../includes/sqlite3/md5func.py
create_aggregate(name, num_params, aggregate_class)
Creates a user-defined aggregate function.
The aggregate class must implement a step
method, which accepts the number of parameters num_params (if num_params is -1, the function may take any number of arguments), and a finalize
method which will return the final result of the aggregate.
The finalize
method can return any of the types supported by SQLite: bytes, str, int, float and None
.
Example:
../includes/sqlite3/mysumaggr.py
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 windowvalue
: returns the current value of the aggregateinverse
: removes a row from the current windowfinalize
: 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: bytes
, str
, int
, float
, and None
. Call create_window_function
with aggregate_class set to None
to clear window function name.
Aggregate window functions are supported by SQLite 3.25.0 and higher. NotSupportedError
will be raised if used with older versions.
3.11
Example:
../includes/sqlite3/sumintwindow.py
create_collation(name, callable)
Create a collation named name using the collating function callable. callable is passed two string <str>
arguments, and it should return an integer <int>
:
1
if the first is ordered higher than the second-1
if the first is ordered lower than the second0
if they are ordered equal
The following example shows a reverse sorting collation:
../includes/sqlite3/collation_reverse.py
Remove a collation function by setting callable to None
.
3.11 The collation name can contain any Unicode character. Earlier, only ASCII characters were allowed.
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.
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 SQLITE_OK
if access is allowed, SQLITE_DENY
if the entire SQL statement should be aborted with an error and SQLITE_IGNORE
if the column should be treated as a NULL value. These constants are available in the 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 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 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 sqlite3
module.
Passing None
as authorizer_callback will disable the authorizer.
3.11 Added support for disabling the authorizer using None
.
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 None
for handler.
Returning a non-zero value from the handler function will terminate the currently executing query and cause it to raise an OperationalError
exception.
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 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 Cursor.execute
methods. Other sources include the transaction management <sqlite3-controlling-transactions>
of the sqlite3 module and the execution of triggers defined in the current database.
Passing 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 ~sqlite3.enable_callback_tracebacks
to enable printing tracebacks from exceptions raised in the trace callback.
3.3
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. See1.
sqlite3.enable_load_extension connection,enabled sqlite3.enable_load_extension
3.2
3.10 Added the sqlite3.enable_load_extension
auditing event.
../includes/sqlite3/load_extension.py
load_extension(path)
This routine loads an SQLite extension from a shared library. You have to enable extension loading with enable_load_extension
before you can use this routine.
Loadable extensions are disabled by default. See2.
sqlite3.load_extension connection,path sqlite3.load_extension
3.2
3.10 Added the sqlite3.load_extension
auditing event.
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:
../includes/sqlite3/row_factory.py
If returning a tuple doesn't suffice and you want name-based access to columns, you should consider setting row_factory
to the highly-optimized sqlite3.Row
type. 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.
text_factory
Using this attribute you can control what objects are returned for the TEXT
data type. By default, this attribute is set to str
and the sqlite3
module will return str
objects for TEXT
. If you want to return bytes
instead, you can set it to 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:
../includes/sqlite3/text_factory.py
total_changes
Returns the total number of database rows that have been modified, inserted, or deleted since the database connection was opened.
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 .dump
command in the 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()
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 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)
3.7
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}")
3.11
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)
3.11
serialize(*, name="main")
This method serializes a database into a 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.
3.11
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 OperationalError
if the database connection is currently involved in a read transaction or a backup operation. OverflowError
will be raised if len(data)
is larger than 2**63 - 1
, and 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.
3.11
A Cursor
instance has the following attributes and methods.
single: ? (question mark); in SQL statements
single: : (colon); in SQL statements
execute(sql[, parameters])
Executes an SQL statement. Values may be bound to the statement using placeholders <sqlite3-placeholders>
.
execute
will only execute a single SQL statement. If you try to execute more than one statement with it, it will raise a ProgrammingError
. Use executescript
if you want to execute multiple SQL statements with one call.
executemany(sql, seq_of_parameters)
Executes a parameterized <sqlite3-placeholders>
SQL command against all parameter sequences or mappings found in the sequence seq_of_parameters. The sqlite3
module also allows using an iterator
yielding parameters instead of a sequence.
../includes/sqlite3/executemany_1.py
Here's a shorter example using a generator
:
../includes/sqlite3/executemany_2.py
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 isolation_level
; any transaction control must be added to sql_script.
sql_script can be an instance of str
.
Example:
../includes/sqlite3/executescript.py
fetchone()
Fetches the next row of a query result set, returning a single sequence, or None
when no more data is available.
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 fetchmany
call to the next.
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.
close()
Close the cursor now (rather than whenever __del__
is called).
The cursor will be unusable from this point forward; a ProgrammingError
exception will be raised if any operation is attempted with the cursor.
setinputsizes(sizes)
Required by the DB-API. Does nothing in sqlite3
.
setoutputsize(size [, column])
Required by the DB-API. Does nothing in sqlite3
.
rowcount
Although the Cursor
class of the sqlite3
module implements this attribute, the database engine's own support for the determination of "rows affected"/"rows selected" is quirky.
For executemany
statements, the number of modifications are summed up into rowcount
.
As required by the Python DB API Spec, the 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.
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 execute
method. For other statements, after executemany
or executescript
, or if the insertion failed, the value of lastrowid
is left unchanged. The initial value of lastrowid
is None
.
Note
Inserts into WITHOUT ROWID
tables are not recorded.
3.6 Added support for the REPLACE
statement.
arraysize
Read/write attribute that controls the number of rows returned by fetchmany
. The default value is 1 which means a single row would be fetched per call.
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 None
.
It is set for SELECT
statements without any matching rows as well.
connection
This read-only attribute provides the SQLite database Connection
used by the Cursor
object. A Cursor
object created by calling con.cursor() <Connection.cursor>
will have a connection
attribute that refers to con:
>>> con = sqlite3.connect(":memory:")
>>> cur = con.cursor()
>>> cur.connection == con
True
A Row
instance serves as a highly optimized ~Connection.row_factory
for 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 len
.
If two Row
objects have exactly the same columns and their members are equal, they compare equal.
keys
This method returns a list of column names. Immediately after a query, it is the first member of each tuple in Cursor.description
.
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 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
3.11
A Blob
instance is a file-like object
that can read and write data in an SQLite BLOB (Binary Large OBject)
. Call len(blob) <len>
to get the size (number of bytes) of the blob. Use indices and slices <slice>
for direct access to the blob data.
Use the Blob
as a context manager
to ensure that the blob handle is closed after use.
../includes/sqlite3/blob.py
close()
Close the blob.
The blob will be unusable from this point onward. An ~sqlite3.Error
(or subclass) exception will be raised if any further operation is attempted with the blob.
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 EOF (End of File)
will be returned. When length is not specified, or is negative, ~Blob.read
will read until the end of the blob.
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 ValueError
.
tell()
Return the current access position of the blob.
seek(offset, origin=os.SEEK_SET, /)
Set the current access position of the blob to offset. The origin argument defaults to os.SEEK_SET
(absolute blob positioning). Other values for origin are os.SEEK_CUR
(seek relative to the current position) and os.SEEK_END
(seek relative to the blob’s end).
The exception hierarchy is defined by the DB-API 2.0 (249
).
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 Exception
.
Error
The base class of the other exceptions in this module. Use this to catch all errors with one single except
statement. Error
is a subclass of 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 Error
.
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 Error
.
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 DatabaseError
.
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 DatabaseError
.
IntegrityError
Exception raised when the relational integrity of the database is affected, e.g. a foreign key check fails. It is a subclass of DatabaseError
.
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 DatabaseError
.
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 Connection
. ProgrammingError
is a subclass of DatabaseError
.
NotSupportedError
Exception raised in case a method or database API is not supported by the underlying SQLite library. For example, setting deterministic to True
in ~Connection.create_function
, if the underlying SQLite library does not support deterministic functions. NotSupportedError
is a subclass of 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 |
---|---|
None |
NULL |
int |
INTEGER |
float |
REAL |
str |
TEXT |
bytes |
BLOB |
This is how SQLite types are converted to Python types by default:
SQLite type | Python type |
---|---|
NULL |
None |
INTEGER |
int |
REAL |
float |
TEXT |
depends on ~Connection.text_factory , str by default |
BLOB |
bytes |
The type system of the 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 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 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 PrepareProtocol
.
../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 register_adapter
.
../includes/sqlite3/adapter_point_2.py
The sqlite3
module has two default adapters for Python's built-in datetime.date
and datetime.datetime
types. Now let's suppose we want to store datetime.datetime
objects not in ISO representation, but as a Unix timestamp.
../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 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 Point
object from it.
Note
Converter functions always get called with a 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 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 sqlite3-module-contents
, in the entries for the constants PARSE_DECLTYPES
and PARSE_COLNAMES
.
The following example illustrates both approaches.
../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 datetime.date
and under the name "timestamp" for 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.
../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 datetime.datetime
object. To preserve UTC offsets in timestamps, either leave converters disabled, or register an offset-aware converter with register_converter
.
The underlying sqlite3
library operates in autocommit
mode by default, but the Python 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 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 sqlite3
implicitly executes via the isolation_level parameter to the connect
call, or via the 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 sqlite3
module's implicit transaction management by setting 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 ~Cursor.executescript
disregards isolation_level
; any transaction control must be added explicitly.
3.6 sqlite3
used to implicitly commit an open transaction before DDL statements. This is no longer the case.
Using the nonstandard execute
, executemany
and executescript
methods of the Connection
object, your code can be written more concisely because you don't have to create the (often superfluous) Cursor
objects explicitly. Instead, the 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 Connection
object.
../includes/sqlite3/shortcut_methods.py
One useful feature of the sqlite3
module is the built-in 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:
../includes/sqlite3/rowclass.py
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:
../includes/sqlite3/ctx_manager.py
Footnotes
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
--enable-loadable-sqlite-extensions
option to configure.↩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
--enable-loadable-sqlite-extensions
option to configure.↩