sqlite3 — DB-API 2.0 interface for SQLite databases¶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 a SQL interface compliant with the DB-API 2.0 specification described by PEP 249.
To use the module, you must first create a Connection object that
represents the database. Here the data will be stored in the
example.db file:
import sqlite3
conn = sqlite3.connect('example.db')
You can also supply the special name :memory: to create a database in RAM.
Once you have a Connection, you can create a Cursor object
and call its execute() method to perform SQL commands:
c = conn.cursor()
# Create table
c.execute('''CREATE TABLE stocks
(date text, trans text, symbol text, qty real, price real)''')
# Insert a row of data
c.execute("INSERT INTO stocks VALUES ('2006-01-05','BUY','RHAT',100,35.14)")
# Save (commit) the changes
conn.commit()
# We can also close the connection if we are done with it.
# Just be sure any changes have been committed or they will be lost.
conn.close()
The data you’ve saved is persistent and is available in subsequent sessions:
import sqlite3
conn = sqlite3.connect('example.db')
c = conn.cursor()
Usually your SQL operations will need to use values from Python variables. You shouldn’t assemble your query using Python’s string operations because doing so is insecure; it makes your program vulnerable to an SQL injection attack (see https://xkcd.com/327/ for humorous example of what can go wrong).
Instead, use the DB-API’s parameter substitution. Put ? as a placeholder
wherever you want to use a value, and then provide a tuple of values as the
second argument to the cursor’s execute() method. (Other database
modules may use a different placeholder, such as %s or :1.) For
example:
# Never do this -- insecure!
symbol = 'RHAT'
c.execute("SELECT * FROM stocks WHERE symbol = '%s'" % symbol)
# Do this instead
t = ('RHAT',)
c.execute('SELECT * FROM stocks WHERE symbol=?', t)
print(c.fetchone())
# Larger example that inserts many records at a time
purchases = [('2006-03-28', 'BUY', 'IBM', 1000, 45.00),
('2006-04-05', 'BUY', 'MSFT', 1000, 72.00),
('2006-04-06', 'SELL', 'IBM', 500, 53.00),
]
c.executemany('INSERT INTO stocks VALUES (?,?,?,?,?)', purchases)
To retrieve data after executing a SELECT statement, you can either treat the
cursor as an iterator, call the cursor’s fetchone() method to
retrieve a single matching row, or call fetchall() to get a list of the
matching rows.
This example uses the iterator form:
>>> for row in c.execute('SELECT * FROM stocks ORDER BY price'):
print(row)
('2006-01-05', 'BUY', 'RHAT', 100, 35.14)
('2006-03-28', 'BUY', 'IBM', 1000, 45.0)
('2006-04-06', 'SELL', 'IBM', 500, 53.0)
('2006-04-05', 'BUY', 'MSFT', 1000, 72.0)
See also
sqlite3.version¶The version number of this module, as a string. This is not the version of the SQLite library.
sqlite3.version_info¶The version number of this module, as a tuple of integers. This is not the version of the SQLite library.
sqlite3.sqlite_version¶The version number of the run-time SQLite library, as a string.
sqlite3.sqlite_version_info¶The version number of the run-time SQLite library, as a tuple of integers.
sqlite3.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.
sqlite3.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
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”.
sqlite3.connect(database[, timeout, detect_types, isolation_level, check_same_thread, factory, cached_statements, uri])¶Opens a connection to the SQLite database file database. You can use
":memory:" to open a database connection to a database that resides in RAM
instead of on disk.
When a database is accessed by multiple connections, and one of the processes modifies the database, the SQLite database is locked until that transaction is committed. The timeout parameter specifies how long the connection should wait for the lock to go away until raising an exception. The default for the timeout parameter is 5.0 (five seconds).
For the isolation_level parameter, please see the
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.
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 SQLite and Python 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 100 statements.
If uri is true, database is interpreted as a URI. This allows you to specify options. For example, to open a database in read-only mode you can use:
db = sqlite3.connect('file:path/to/database?mode=ro', uri=True)
More information about this feature, including a list of recognized options, can be found in the SQLite URI documentation.
Changed in version 3.4: Added the uri parameter.
sqlite3.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 the case of typename and
the name of the type in your query must match!
sqlite3.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.
sqlite3.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:
# A minimal SQLite shell for experiments
import sqlite3
con = sqlite3.connect(":memory:")
con.isolation_level = None
cur = con.cursor()
buffer = ""
print("Enter your SQL commands to execute in sqlite3.")
print("Enter a blank line to exit.")
while True:
line = input()
if line == "":
break
buffer += line
if sqlite3.complete_statement(buffer):
try:
buffer = buffer.strip()
cur.execute(buffer)
if buffer.lstrip().upper().startswith("SELECT"):
print(cur.fetchall())
except sqlite3.Error as e:
print("An error occurred:", e.args[0])
buffer = ""
con.close()
sqlite3.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.
sqlite3.Connection¶A SQLite database connection has the following attributes and methods:
isolation_level¶Get or set the current isolation level. None for autocommit mode or
one of “DEFERRED”, “IMMEDIATE” or “EXCLUSIVE”. See section
Controlling Transactions for a more detailed explanation.
in_transaction¶True if a transaction is active (there are uncommitted changes),
False otherwise. Read-only attribute.
New in version 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.
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.
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])¶This is a nonstandard shortcut that creates a cursor object by calling
the cursor() method, calls the cursor’s
execute() method with the parameters given, and returns
the cursor.
executemany(sql[, parameters])¶This is a nonstandard shortcut that creates a cursor object by
calling the cursor() method, calls the cursor’s
executemany() method with the parameters given, and
returns the cursor.
executescript(sql_script)¶This is a nonstandard shortcut that creates a cursor object by
calling the cursor() method, calls the cursor’s
executescript() method with the given sql_script, and
returns the cursor.
create_function(name, num_params, func)¶Creates a user-defined function that you can later use from within SQL statements under the function name name. num_params is the number of parameters the function accepts (if num_params is -1, the function may take any number of arguments), and func is a Python callable that is called as the SQL function.
The function can return any of the types supported by SQLite: bytes, str, int,
float and None.
Example:
import sqlite3
import hashlib
def md5sum(t):
return hashlib.md5(t).hexdigest()
con = sqlite3.connect(":memory:")
con.create_function("md5", 1, md5sum)
cur = con.cursor()
cur.execute("select md5(?)", (b"foo",))
print(cur.fetchone()[0])
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:
import sqlite3
class MySum:
def __init__(self):
self.count = 0
def step(self, value):
self.count += value
def finalize(self):
return self.count
con = sqlite3.connect(":memory:")
con.create_aggregate("mysum", 1, MySum)
cur = con.cursor()
cur.execute("create table test(i)")
cur.execute("insert into test(i) values (1)")
cur.execute("insert into test(i) values (2)")
cur.execute("select mysum(i) from test")
print(cur.fetchone()[0])
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”:
import sqlite3
def collate_reverse(string1, string2):
if string1 == string2:
return 0
elif string1 < string2:
return 1
else:
return -1
con = sqlite3.connect(":memory:")
con.create_collation("reverse", collate_reverse)
cur = con.cursor()
cur.execute("create table test(x)")
cur.executemany("insert into test(x) values (?)", [("a",), ("b",)])
cur.execute("select x from test order by x collate reverse")
for row in cur:
print(row)
con.close()
To remove a collation, call create_collation with None as callable:
con.create_collation("reverse", None)
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.
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.
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.
set_trace_callback(trace_callback)¶Registers trace_callback to be called for each SQL statement that is actually executed by the SQLite backend.
The only argument passed to the callback is the statement (as string) that
is being executed. The return value of the callback is ignored. Note that
the backend does not only run statements passed to the Cursor.execute()
methods. Other sources include the transaction management of the Python
module and the execution of triggers defined in the current database.
Passing None as trace_callback will disable the trace callback.
New in version 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. See [1].
New in version 3.2.
import sqlite3
con = sqlite3.connect(":memory:")
# enable extension loading
con.enable_load_extension(True)
# Load the fulltext search extension
con.execute("select load_extension('./fts3.so')")
# alternatively you can load the extension using an API call:
# con.load_extension("./fts3.so")
# disable extension laoding again
con.enable_load_extension(False)
# example from SQLite wiki
con.execute("create virtual table recipe using fts3(name, ingredients)")
con.executescript("""
insert into recipe (name, ingredients) values ('broccoli stew', 'broccoli peppers cheese tomatoes');
insert into recipe (name, ingredients) values ('pumpkin stew', 'pumpkin onions garlic celery');
insert into recipe (name, ingredients) values ('broccoli pie', 'broccoli cheese onions flour');
insert into recipe (name, ingredients) values ('pumpkin pie', 'pumpkin sugar flour butter');
""")
for row in con.execute("select rowid, name, ingredients from recipe where name match 'pie'"):
print(row)
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.
Loadable extensions are disabled by default. See [1].
New in version 3.2.
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:
import sqlite3
def dict_factory(cursor, row):
d = {}
for idx, col in enumerate(cursor.description):
d[col[0]] = row[idx]
return d
con = sqlite3.connect(":memory:")
con.row_factory = dict_factory
cur = con.cursor()
cur.execute("select 1 as a")
print(cur.fetchone()["a"])
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 Unicode objects for TEXT. If you want to
return bytestrings 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:
import sqlite3
con = sqlite3.connect(":memory:")
cur = con.cursor()
AUSTRIA = "\xd6sterreich"
# by default, rows are returned as Unicode
cur.execute("select ?", (AUSTRIA,))
row = cur.fetchone()
assert row[0] == AUSTRIA
# but we can make sqlite3 always return bytestrings ...
con.text_factory = bytes
cur.execute("select ?", (AUSTRIA,))
row = cur.fetchone()
assert type(row[0]) is bytes
# the bytestrings will be encoded in UTF-8, unless you stored garbage in the
# database ...
assert row[0] == AUSTRIA.encode("utf-8")
# we can also implement a custom text_factory ...
# here we implement one that appends "foo" to all strings
con.text_factory = lambda x: x.decode("utf-8") + "foo"
cur.execute("select ?", ("bar",))
row = cur.fetchone()
assert row[0] == "barfoo"
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)
sqlite3.Cursor¶A Cursor instance has the following attributes and methods.
execute(sql[, parameters])¶Executes an SQL statement. The SQL statement may be parameterized (i. e.
placeholders instead of SQL literals). The sqlite3 module supports two
kinds of placeholders: question marks (qmark style) and named placeholders
(named style).
Here’s an example of both styles:
import sqlite3
con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.execute("create table people (name_last, age)")
who = "Yeltsin"
age = 72
# This is the qmark style:
cur.execute("insert into people values (?, ?)", (who, age))
# And this is the named style:
cur.execute("select * from people where name_last=:who and age=:age", {"who": who, "age": age})
print(cur.fetchone())
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
executescript() if you want to execute multiple SQL statements with one
call.
executemany(sql, seq_of_parameters)¶Executes an 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.
import sqlite3
class IterChars:
def __init__(self):
self.count = ord('a')
def __iter__(self):
return self
def __next__(self):
if self.count > ord('z'):
raise StopIteration
self.count += 1
return (chr(self.count - 1),) # this is a 1-tuple
con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.execute("create table characters(c)")
theIter = IterChars()
cur.executemany("insert into characters(c) values (?)", theIter)
cur.execute("select c from characters")
print(cur.fetchall())
Here’s a shorter example using a generator:
import sqlite3
import string
def char_generator():
for c in string.ascii_lowercase:
yield (c,)
con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.execute("create table characters(c)")
cur.executemany("insert into characters(c) values (?)", char_generator())
cur.execute("select c from characters")
print(cur.fetchall())
executescript(sql_script)¶This is a nonstandard convenience method for executing multiple SQL statements
at once. It issues a COMMIT statement first, then executes the SQL script it
gets as a parameter.
sql_script can be an instance of str.
Example:
import sqlite3
con = sqlite3.connect(":memory:")
cur = con.cursor()
cur.executescript("""
create table person(
firstname,
lastname,
age
);
create table book(
title,
author,
published
);
insert into book(title, author, published)
values (
'Dirk Gently''s Holistic Detective Agency',
'Douglas Adams',
1987
);
""")
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.
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.
With SQLite versions before 3.6.5, rowcount is set to 0 if
you make a DELETE FROM table without any condition.
lastrowid¶This read-only attribute provides the rowid of the last modified row. It is
only set if you issued an INSERT or a REPLACE statement using the
execute() method. For operations other than INSERT or
REPLACE or when executemany() is called, lastrowid is
set to None.
If the INSERT or REPLACE statement failed to insert the previous
successful rowid is returned.
Changed in version 3.6: Added support for the REPLACE statement.
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() will have a
connection attribute that refers to con:
>>> con = sqlite3.connect(":memory:")
>>> cur = con.cursor()
>>> cur.connection == con
True
sqlite3.Row¶A Row instance serves as a highly optimized
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.
Changed in version 3.5: Added support of slicing.
Let’s assume we initialize a table as in the example given above:
conn = sqlite3.connect(":memory:")
c = conn.cursor()
c.execute('''create table stocks
(date text, trans text, symbol text,
qty real, price real)''')
c.execute("""insert into stocks
values ('2006-01-05','BUY','RHAT',100,35.14)""")
conn.commit()
c.close()
Now we plug Row in:
>>> conn.row_factory = sqlite3.Row
>>> c = conn.cursor()
>>> c.execute('select * from stocks')
<sqlite3.Cursor object at 0x7f4e7dd8fa80>
>>> r = c.fetchone()
>>> type(r)
<class 'sqlite3.Row'>
>>> tuple(r)
('2006-01-05', 'BUY', 'RHAT', 100.0, 35.14)
>>> len(r)
5
>>> r[2]
'RHAT'
>>> r.keys()
['date', 'trans', 'symbol', 'qty', 'price']
>>> r['qty']
100.0
>>> for member in r:
... print(member)
...
2006-01-05
BUY
RHAT
100.0
35.14
sqlite3.Error¶The base class of the other exceptions in this module. It is a subclass
of Exception.
sqlite3.DatabaseError¶Exception raised for errors that are related to the database.
sqlite3.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.
sqlite3.ProgrammingError¶Exception raised for programming errors, e.g. table not found or already
exists, syntax error in the SQL statement, wrong number of parameters
specified, etc. It 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 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 a 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 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 PrepareProtocol.
import sqlite3
class Point:
def __init__(self, x, y):
self.x, self.y = x, y
def __conform__(self, protocol):
if protocol is sqlite3.PrepareProtocol:
return "%f;%f" % (self.x, self.y)
con = sqlite3.connect(":memory:")
cur = con.cursor()
p = Point(4.0, -3.2)
cur.execute("select ?", (p,))
print(cur.fetchone()[0])
The other possibility is to create a function that converts the type to the
string representation and register the function with register_adapter().
import sqlite3
class Point:
def __init__(self, x, y):
self.x, self.y = x, y
def adapt_point(point):
return "%f;%f" % (point.x, point.y)
sqlite3.register_adapter(Point, adapt_point)
con = sqlite3.connect(":memory:")
cur = con.cursor()
p = Point(4.0, -3.2)
cur.execute("select ?", (p,))
print(cur.fetchone()[0])
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.
import sqlite3
import datetime
import time
def adapt_datetime(ts):
return time.mktime(ts.timetuple())
sqlite3.register_adapter(datetime.datetime, adapt_datetime)
con = sqlite3.connect(":memory:")
cur = con.cursor()
now = datetime.datetime.now()
cur.execute("select ?", (now,))
print(cur.fetchone()[0])
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:
Both ways are described in section Module functions and constants, in the entries
for the constants PARSE_DECLTYPES and PARSE_COLNAMES.
The following example illustrates both approaches.
import sqlite3
class Point:
def __init__(self, x, y):
self.x, self.y = x, y
def __repr__(self):
return "(%f;%f)" % (self.x, self.y)
def adapt_point(point):
return ("%f;%f" % (point.x, point.y)).encode('ascii')
def convert_point(s):
x, y = list(map(float, s.split(b";")))
return Point(x, y)
# Register the adapter
sqlite3.register_adapter(Point, adapt_point)
# Register the converter
sqlite3.register_converter("point", convert_point)
p = Point(4.0, -3.2)
#########################
# 1) Using declared types
con = sqlite3.connect(":memory:", detect_types=sqlite3.PARSE_DECLTYPES)
cur = con.cursor()
cur.execute("create table test(p point)")
cur.execute("insert into test(p) values (?)", (p,))
cur.execute("select p from test")
print("with declared types:", cur.fetchone()[0])
cur.close()
con.close()
#######################
# 1) Using column names
con = sqlite3.connect(":memory:", detect_types=sqlite3.PARSE_COLNAMES)
cur = con.cursor()
cur.execute("create table test(p)")
cur.execute("insert into test(p) values (?)", (p,))
cur.execute('select p as "p [point]" from test')
print("with column names:", cur.fetchone()[0])
cur.close()
con.close()
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.
import sqlite3
import datetime
con = sqlite3.connect(":memory:", detect_types=sqlite3.PARSE_DECLTYPES|sqlite3.PARSE_COLNAMES)
cur = con.cursor()
cur.execute("create table test(d date, ts timestamp)")
today = datetime.date.today()
now = datetime.datetime.now()
cur.execute("insert into test(d, ts) values (?, ?)", (today, now))
cur.execute("select d, ts from test")
row = cur.fetchone()
print(today, "=>", row[0], type(row[0]))
print(now, "=>", row[1], type(row[1]))
cur.execute('select current_date as "d [date]", current_timestamp as "ts [timestamp]"')
row = cur.fetchone()
print("current_date", row[0], type(row[0]))
print("current_timestamp", row[1], type(row[1]))
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.
By default, the sqlite3 module opens transactions 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
(or none at all) via the isolation_level parameter to the connect()
call, or via the isolation_level property of connections.
If you want autocommit mode, then set 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”.
The current transaction state is exposed through the
Connection.in_transaction attribute of the connection object.
Changed in version 3.6: sqlite3 used to implicitly commit an open transaction before DDL
statements. This is no longer the case.
sqlite3 efficiently¶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.
import sqlite3
persons = [
("Hugo", "Boss"),
("Calvin", "Klein")
]
con = sqlite3.connect(":memory:")
# Create the table
con.execute("create table person(firstname, lastname)")
# Fill the table
con.executemany("insert into person(firstname, lastname) values (?, ?)", persons)
# Print the table contents
for row in con.execute("select firstname, lastname from person"):
print(row)
print("I just deleted", con.execute("delete from person").rowcount, "rows")
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:
import sqlite3
con = sqlite3.connect(":memory:")
con.row_factory = sqlite3.Row
cur = con.cursor()
cur.execute("select 'John' as name, 42 as age")
for row in cur:
assert row[0] == row["name"]
assert row["name"] == row["nAmE"]
assert row[1] == row["age"]
assert row[1] == row["AgE"]
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:
import sqlite3
con = sqlite3.connect(":memory:")
con.execute("create table person (id integer primary key, firstname varchar unique)")
# Successful, con.commit() is called automatically afterwards
with con:
con.execute("insert into person(firstname) values (?)", ("Joe",))
# con.rollback() is called after the with block finishes with an exception, the
# exception is still raised and must be caught
try:
with con:
con.execute("insert into person(firstname) values (?)", ("Joe",))
except sqlite3.IntegrityError:
print("couldn't add Joe twice")
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 interrupt() method, which
only makes sense to call from a different thread.
Footnotes
| [1] | (1, 2) The sqlite3 module is not built with loadable extension support by default, because some platforms (notably Mac OS X) have SQLite libraries which are compiled without this feature. To get loadable extension support, you must pass –enable-loadable-sqlite-extensions to configure. |