# `sqlite3` — DB-API 2.0 interfaz para bases de datos SQLite

Código fuente: Lib/sqlite3/

## Introducción

SQLite es una biblioteca de C que provee una base de datos ligera basada en disco que no requiere un proceso de servidor separado y permite acceder a la base de datos usando una variación no estándar del lenguaje de consulta SQL. Algunas aplicaciones pueden usar SQLite para almacenamiento interno. También es posible prototipar una aplicación usando SQLite y luego transferir el código a una base de datos más grande como PostgreSQL u 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.

This document includes four main sections:

- Tutorial teaches how to use the sqlite3 module.

- Reference describes the classes and functions this module defines.

- How-to guides details how to handle specific tasks.

- Explanation provides in-depth background on transaction control.

## Tutorial

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 `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()

At this point, our database only contains one row:

    >>> res = cur.execute('SELECT count(rowid) FROM stocks')
    >>> print(res.fetchone())
    (1,)

The result is a one-item `tuple`: one row, with one column. Now, let us insert three more rows of data, using `executemany()`:

    >>> data = [
    ...    ('2006-03-28', 'BUY', 'IBM', 1000, 45.0),
    ...    ('2006-04-05', 'BUY', 'MSFT', 1000, 72.0),
    ...    ('2006-04-06', 'SELL', 'IBM', 500, 53.0),
    ... ]
    >>> cur.executemany('INSERT INTO stocks VALUES(?, ?, ?, ?, ?)', data)

Then, retrieve the data by iterating over the result of a `SELECT` statement:

    >>> 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 `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. For the named style, it can be either a sequence or `dict` instance. The length of the 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:

    import sqlite3

    con = sqlite3.connect(":memory:")
    cur = con.cursor()
    cur.execute("create table lang (name, first_appeared)")

    # This is the qmark style:
    cur.execute("insert into lang values (?, ?)", ("C", 1972))

    # The qmark style used with executemany():
    lang_list = [
        ("Fortran", 1957),
        ("Python", 1991),
        ("Go", 2009),
    ]
    cur.executemany("insert into lang values (?, ?)", lang_list)

    # And this is the named style:
    cur.execute("select * from lang where first_appeared=:year", {"year": 1972})
    print(cur.fetchall())

    con.close()

Ver también

https://www.sqlite.org

  La página web SQLite; la documentación describe la sintaxis y los tipos de datos disponibles para el lenguaje SQL soportado.

https://www.w3schools.com/sql/

  Tutorial, referencia y ejemplos para aprender sintaxis SQL.

PEP 249 - Especificación de la API 2.0 de base de datos

  PEP escrito por Marc-André Lemburg.

## Reference

### Funciones y constantes del módulo

`sqlite3.``apilevel`

  String constant stating the supported DB-API level. Required by the DB-API. Hard-coded to `"2.0"`.

`sqlite3.``paramstyle`

  String constant stating the type of parameter marker formatting expected by the `sqlite3` module. Required by the DB-API. Hard-coded to `"qmark"`.

  Nota

  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.

`sqlite3.``version`

  Version number of this module as a `string`. This is not the version of the SQLite library.

`sqlite3.``version_info`

  Version number of this module as a `tuple` of `integers`. This is not the version of the SQLite library.

`sqlite3.``sqlite_version`

  Version number of the runtime SQLite library as a `string`.

`sqlite3.``sqlite_version_info`

  Version number of the runtime SQLite library as a `tuple` of `integers`.

`sqlite3.``threadsafety`

  Integer constant required by the DB-API, stating the level of thread safety the `sqlite3` module supports. Currently hard-coded to `1`, meaning «Threads may share the module, but not connections.» However, this may not always be true. You can check the underlying SQLite library’s compile-time threaded mode using the following query:

      import sqlite3
      con = sqlite3.connect(":memory:")
      con.execute("""
          select * from pragma_compile_options
          where compile_options like 'THREADSAFE=%'
      """).fetchall()

  Note that the SQLITE_THREADSAFE levels do not match the DB-API 2.0 `threadsafety` levels.

`sqlite3.``PARSE_DECLTYPES`

  Pass this flag value to the detect_types parameter of `connect()` to look up a converter function using the declared types for each column. The types are declared when the database table is created. `sqlite3` will look up a converter function using the first word of the declared type as the converter dictionary key. For example:

      CREATE TABLE test(
         i integer primary key,  ! will look up a converter named "integer"
         p point,                ! will look up a converter named "point"
         n number(10)            ! will look up a converter named "number"
       )

  This flag may be combined with `PARSE_COLNAMES` using the `|` (bitwise or) operator.

`sqlite3.``PARSE_COLNAMES`

  Pass this flag value to the detect_types parameter of `connect()` to look up a converter function by using the type name, parsed from the query column name, as the converter dictionary key. The type name must be wrapped in square brackets (`[]`).

      SELECT p as "p [point]" FROM test;  ! will look up converter "point"

  This flag may be combined with `PARSE_DECLTYPES` using the `|` (bitwise or) operator.

`sqlite3.``connect`(database, timeout=5.0, detect_types=0, isolation_level='DEFERRED', check_same_thread=True, factory=sqlite3.Connection, cached_statements=128, uri=False)

  Open a connection to an SQLite database.

  Parámetros

    - database (path-like object) – The path to the database file to be opened. Pass `":memory:"` to open a connection to a database that is in RAM instead of on disk.

    - timeout (float) – How many seconds the connection should wait before raising an exception, if the database is locked by another connection. If another connection opens a transaction to modify the database, it will be locked until that transaction is committed. Default five seconds.

    - detect_types (int) – Control whether and how data types not natively supported by SQLite are looked up to be converted to Python types, using the converters registered with `register_converter()`. Set it to any combination (using `|`, bitwise or) of `PARSE_DECLTYPES` and `PARSE_COLNAMES` to enable this. Column names takes precedence over declared types if both flags are set. Types cannot be detected for generated fields (for example `max(data)`), even when the detect_types parameter is set; `str` will be returned instead. By default (`0`), type detection is disabled.

    - isolation_level (str | `None`) – The `isolation_level` of the connection, controlling whether and how transactions are implicitly opened. Can be `"DEFERRED"` (default), `"EXCLUSIVE"` or `"IMMEDIATE"`; or `None` to disable opening transactions implicitly. See Transaction control for more.

    - check_same_thread (bool) – If `True` (default), only the creating thread may use the connection. If `False`, the connection may be shared across multiple threads; if so, write operations should be serialized by the user to avoid data corruption.

    - factory (`Connection`) – A custom subclass of `Connection` to create the connection with, if not the default `Connection` class.

    - cached_statements (int) – The number of statements that `sqlite3` should internally cache for this connection, to avoid parsing overhead. By default, 100 statements.

    - uri (bool) – If set to `True`, database is interpreted as a URI with a file path and an optional query string. The scheme part must be `"file:"`, and the path can be relative or absolute. The query string allows passing parameters to SQLite, enabling various Working with SQLite URIs.

  Tipo del valor devuelto

    Connection

  Lanza un evento de auditoría `sqlite3.connect` con argumento `database`.

  Lanza un auditing event `sqlite3.connect/handle` con el argumento `connection_handle`.

  Nuevo en la versión 3.4: The uri parameter.

  Distinto en la versión 3.7: database ahora también puede ser un path-like object, no solo una cadena de caracteres.

  Nuevo en la versión 3.10: The `sqlite3.connect/handle` auditing event.

`sqlite3.``register_converter`(typename, converter, /)

  Register the converter callable to convert SQLite objects of type typename into a Python object of a specific type. The converter is invoked for all SQLite values of type typename; it is passed a `bytes` object and should return an object of the desired Python type. Consult the parameter detect_types of `connect()` for information regarding how type detection works.

  Note: typename and the name of the type in your query are matched case-insensitively.

`sqlite3.``register_adapter`(type, adapter, /)

  Register an adapter callable to adapt the Python type type into an SQLite type. The adapter is called with a Python object of type type as its sole argument, and must return a value of a type that SQLite natively understands.

`sqlite3.``complete_statement`(statement)

  Returns `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.

  Esto puede ser usado para construir un shell para SQLite, como en el siguiente ejemplo:

      # 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, /)

  Enable or disable callback tracebacks. 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.

### Connection objects

class `sqlite3.``Connection`

  Each open SQLite database is represented by a `Connection` object, which is created using `sqlite3.connect()`. Their main purpose is creating `Cursor` objects, and Transaction control.

  Ver también

  - Using connection shortcut methods

  - Usando la conexión como un administrador de contexto

  An SQLite database connection has the following attributes and methods:

  `isolation_level`

    This attribute controls the transaction handling performed by `sqlite3`. If set to `None`, transactions are never implicitly opened. If set to one of `"DEFERRED"`, `"IMMEDIATE"`, or `"EXCLUSIVE"`, corresponding to the underlying SQLite transaction behaviour, implicit transaction management is performed.

    If not overridden by the isolation_level parameter of `connect()`, the default is `""`, which is an alias for `"DEFERRED"`.

  `in_transaction`

    This read-only attribute corresponds to the low-level SQLite autocommit mode.

    `True` if a transaction is active (there are uncommitted changes), `False` otherwise.

    Nuevo en la versión 3.2.

  `cursor`(factory=Cursor)

    Create and return a `Cursor` object. 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`()

    Commit any pending transaction to the database. If there is no open transaction, this method is a no-op.

  `rollback`()

    Roll back to the start of any pending transaction. If there is no open transaction, this method is a no-op.

  `close`()

    Close the database connection. Any pending transaction is not committed implicitly; make sure to `commit()` before closing to avoid losing pending changes.

  `execute`(sql, parameters=(), /)

    Create a new `Cursor` object and call `execute()` on it with the given sql and parameters. Return the new cursor object.

  `executemany`(sql, parameters, /)

    Create a new `Cursor` object and call `executemany()` on it with the given sql and parameters. Return the new cursor object.

  `executescript`(sql_script, /)

    Create a new `Cursor` object and call `executescript()` on it with the given sql_script. Return the new cursor object.

  `create_function`(name, narg, func, *, deterministic=False)

    Create or remove a user-defined SQL function.

    Parámetros

      - name (str) – The name of the SQL function.

      - narg (int) – The number of arguments the SQL function can accept. If `-1`, it may take any number of arguments.

      - func (callback | `None`) – A callable that is called when the SQL function is invoked. The callable must return a type natively supported by SQLite. Set to `None` to remove an existing SQL function.

      - deterministic (bool) – If `True`, the created SQL function is marked as deterministic, which allows SQLite to perform additional optimizations.

    Muestra

      NotSupportedError – If deterministic is used with SQLite versions older than 3.8.3.

    Nuevo en la versión 3.8: The deterministic parameter.

    Ejemplo:

        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])

        con.close()

  `create_aggregate`(name, /, n_arg, aggregate_class)

    Create or remove a user-defined SQL aggregate function.

    Parámetros

      - name (str) – The name of the SQL aggregate function.

      - n_arg (int) – The number of arguments the SQL aggregate function can accept. If `-1`, it may take any number of arguments.

      - aggregate_class (class | `None`) –

        A class must implement the following methods:

        - `step()`: Add a row to the aggregate.

        - `finalize()`: Return the final result of the aggregate as a type natively supported by SQLite.

        The number of arguments that the `step()` method must accept is controlled by n_arg.

        Set to `None` to remove an existing SQL aggregate function.

    Ejemplo:

        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])

        con.close()

  `create_collation`(name, callable)

    Create a collation named name using the collating function callable. callable is passed two `string` arguments, and it should return an `integer`:

    - `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:

        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()

    Remove a collation function by setting callable to `None`.

  `interrupt`()

    Call this method from a different thread to abort any queries that might be executing on the connection. Aborted queries will raise an exception.

  `set_authorizer`(authorizer_callback)

    Register callable authorizer_callback to be 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.

    El primer argumento del callback significa que tipo de operación será autorizada. El segundo y tercer argumento serán argumentos o `None` dependiendo del primer argumento. El cuarto argumento es el nombre de la base de datos («main», «temp», etc.) si aplica. El quinto argumento es el nombre del disparador más interno o vista que es responsable por los intentos de acceso o `None` si este intento de acceso es directo desde el código SQL de entrada.

    Por favor consulte la documentación de SQLite sobre los posibles valores para el primer argumento y el significado del segundo y tercer argumento dependiendo del primero. Todas las constantes necesarias están disponibles en el módulo `sqlite3`.

  `set_progress_handler`(progress_handler, n)

    Register callable progress_handler to be 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 progress_handler.

    Retornando un valor diferente a 0 de la función gestora terminará la actual consulta en ejecución y causará lanzar una excepción `OperationalError`.

  `set_trace_callback`(trace_callback)

    Register callable trace_callback to be invoked for each SQL statement that is actually executed by the SQLite backend.

    El único argumento que se pasa a la devolución de llamada es la declaración (como `str`) que se está ejecutando. El valor de retorno de la devolución de llamada se ignora. Tenga en cuenta que el backend no solo ejecuta declaraciones pasadas a los métodos `Cursor.execute()`. Otras fuentes incluyen el transaction management del módulo sqlite3 y la ejecución de disparadores definidos en la base de datos actual.

    Pasando `None` como trace_callback deshabilitara el trace callback.

    Nota

    Las excepciones que se producen en la llamada de retorno no se propagan. Como ayuda para el desarrollo y la depuración, utilice `enable_callback_tracebacks()` para habilitar la impresión de las trazas de las excepciones que se producen en la llamada de retorno.

    Nuevo en la versión 3.3.

  `enable_load_extension`(enabled, /)

    Enable the SQLite engine to load SQLite extensions from shared libraries if enabled is `True`; else, disallow loading SQLite extensions. 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.

    Nota

    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.

    Lanza un auditing event `sqlite3.enable_load_extension` con argumentos `connection`, `enabled`.

    Nuevo en la versión 3.2.

    Distinto en la versión 3.10: Añadido el evento de auditoría `sqlite3.enable_load_extension`

        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 loading 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)

        con.close()

  `load_extension`(path, /)

    Load an SQLite extension from a shared library located at path. Enable extension loading with `enable_load_extension()` before calling this method.

    Lanza un auditing event `sqlite3.load_extension` con argumentos `connection`, `path`.

    Nuevo en la versión 3.2.

    Distinto en la versión 3.10: Añadido el evento de auditoría `sqlite3.load_extension`

  `row_factory`

    A callable that accepts two arguments, a `Cursor` object and the raw row results as a `tuple`, and returns a custom object representing an SQLite row.

    Ejemplo:

        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"])

        con.close()

    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`

    A callable that accepts a `bytes` parameter and returns a text representation of it. The callable is invoked for SQLite values with the `TEXT` data type. By default, this attribute is set to `str`. If you want to return `bytes` instead, set text_factory to `bytes`.

    Ejemplo:

        import sqlite3

        con = sqlite3.connect(":memory:")
        cur = con.cursor()

        AUSTRIA = "Österreich"

        # by default, rows are returned as str
        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"

        con.close()

  `total_changes`

    Return the total number of database rows that have been modified, inserted, or deleted since the database connection was opened.

  `iterdump`()

    Return an iterator to dump the database as SQL source code. Useful when saving an in-memory database for later restoration. Similar to the `.dump` command in the sqlite3 shell.

    Ejemplo:

        # 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)

    Create a backup of an SQLite database.

    Works even if the database is being accessed by other clients or concurrently by the same connection.

    Parámetros

      - target (Connection) – The database connection to save the backup to.

      - pages (int) – The number of pages to copy at a time. If equal to or less than `0`, the entire database is copied in a single step. Defaults to `-1`.

      - progress (callback | `None`) – If set to a callable, it is invoked with three integer arguments for every backup iteration: the status of the last iteration, the remaining number of pages still to be copied, and the total number of pages. Defaults to `None`.

      - name (str) – The name of the database to back up. Either `"main"` (the default) for the main database, `"temp"` for the temporary database, or the name of a custom database as attached using the `ATTACH DATABASE` SQL statment.

      - sleep (float) – The number of seconds to sleep between successive attempts to back up remaining pages.

    Ejemplo 1, copiar una base de datos existente en otra:

        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()

    Ejemplo 2: copiar una base de datos existente en una copia transitoria:

        import sqlite3

        source = sqlite3.connect('existing_db.db')
        dest = sqlite3.connect(':memory:')
        source.backup(dest)

    Nuevo en la versión 3.7.

### Cursor objects

> A `Cursor` object represents a database cursor which is used to execute SQL statements, and manage the context of a fetch operation. Cursors are created using `Connection.cursor()`, or by using any of the connection shortcut methods.

> Cursor objects are iterators, meaning that if you `execute()` a `SELECT` query, you can simply iterate over the cursor to fetch the resulting rows:

>     for row in cur.execute("select * from data"):
>         print(row)

class `sqlite3.``Cursor`

  Una instancia de `Cursor` tiene los siguientes atributos y métodos.

  `execute`(sql, parameters=(), /)

    Execute SQL statement sql. Bind values to the statement using placeholders that map to the sequence or `dict` parameters.

    `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.

    If `isolation_level` is not `None`, sql is an `INSERT`, `UPDATE`, `DELETE`, or `REPLACE` statement, and there is no open transaction, a transaction is implicitly opened before executing sql.

  `executemany`(sql, parameters, /)

    Execute parameterized SQL statement sql against all parameter sequences or mappings found in the sequence parameters. It is also possible to use an iterator yielding parameters instead of a sequence. Uses the same implicit transaction handling as `execute()`.

    Ejemplo:

        data = [
            ("row1",),
            ("row2",),
        ]
        # cur is an sqlite3.Cursor object
        cur.executemany("insert into t values(?)", data)

  `executescript`(sql_script, /)

    Execute the SQL statements in sql_script. If there is a pending transaciton, an implicit `COMMIT` statement is executed first. No other implicit transaction control is performed; any transaction control must be added to sql_script.

    sql_script must be a `string`.

    Ejemplo:

        # cur is an sqlite3.Cursor object
        cur.executescript("""
            begin;
            create table person(firstname, lastname, age);
            create table book(title, author, published);
            create table publisher(name, address);
            commit;
        """)

  `fetchone`()

    Fetch the next row of a query result set as a `tuple`. Return `None` if no more data is available.

  `fetchmany`(size=cursor.arraysize)

    Fetch the next set of rows of a query result as a `list`. Return an empty list if no more rows are available.

    The number of rows to fetch per call is specified by the size parameter. If size is not given, `arraysize` determines the number of rows to be fetched. If fewer than size rows are available, as many rows as are available are returned.

    Nótese que hay consideraciones de desempeño involucradas con el parámetro size. Para un optimo desempeño, es usualmente mejor usar el atributo arraysize. Si el parámetro size es usado, entonces es mejor retener el mismo valor de una llamada `fetchmany()` a la siguiente.

  `fetchall`()

    Fetch all (remaining) rows of a query result as a `list`. Return an empty list if no rows are available. Note that the `arraysize` attribute can affect the performance of this operation.

  `close`()

    Cierra el cursor ahora (en lugar que cuando `__del__` es llamado)

    El cursor no será usable de este punto en adelante; una excepción `ProgrammingError` será lanzada si se intenta cualquier operación con el cursor.

  `setinputsizes`(sizes, /)

    Required by the DB-API. Does nothing in `sqlite3`.

  `setoutputsize`(size, column=None, /)

    Required by the DB-API. Does nothing in `sqlite3`.

  `rowcount`

    Read-only attribute that provides the number of modified rows for `INSERT`, `UPDATE`, `DELETE`, and `REPLACE` statements; is `-1` for other statements, including CTE queries. It is only updated by the `execute()` and `executemany()` methods.

  `lastrowid`

    Read-only attribute that 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`.

    Nota

    Inserts into `WITHOUT ROWID` tables are not recorded.

    Distinto en la versión 3.6: Se agregó soporte para sentencias `REPLACE`.

  `arraysize`

    Atributo de lectura/escritura que controla el número de filas retornadas por `fetchmany()`. El valor por defecto es 1, lo cual significa que una única fila será obtenida por llamada.

  `description`

    Read-only attribute that 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`.

    También es configurado para sentencias `SELECT` sin ninguna fila coincidente.

  `connection`

    Read-only attribute that provides the SQLite database `Connection` belonging to the cursor. 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

### Row objects

class `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, and supports iteration, `repr()`, equality testing, `len()`, and mapping access by column name and index.

  Two row objects compare equal if have equal columns and equal members.

  `keys`()

    Return a `list` of column names as `strings`. Immediately after a query, it is the first member of each tuple in `Cursor.description`.

  Distinto en la versión 3.5: Agrega soporte de segmentación.

Vamos a asumir que se inicializa una tabla como en el ejemplo dado:

    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()

Ahora conectamos `Row` en:

    >>> 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

### PrepareProtocol objects

class `sqlite3.``PrepareProtocol`

  The PrepareProtocol type’s single purpose is to act as a PEP 246 style adaption protocol for objects that can adapt themselves to native SQLite types.

### Excepciones

The exception hierarchy is defined by the DB-API 2.0 (PEP 249).

exception `sqlite3.``Warning`

  This exception is raised by `sqlite3` if an SQL query is not a `string`, or if multiple statements are passed to `execute()` or `executemany()`. `Warning` is a subclass of `Exception`.

exception `sqlite3.``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`.

exception `sqlite3.``InterfaceError`

  This exception is raised by `sqlite3` for fetch across rollback, or if `sqlite3` is unable to bind parameters. `InterfaceError` is a subclass of `Error`.

exception `sqlite3.``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`.

exception `sqlite3.``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`.

exception `sqlite3.``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`.

exception `sqlite3.``IntegrityError`

  Excepción lanzada cuando la integridad de la base de datos es afectada, por ejemplo la comprobación de una llave foránea falla. Es una subclase de `DatabaseError`.

exception `sqlite3.``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`.

exception `sqlite3.``ProgrammingError`

  Exception raised for `sqlite3` API programming errors, for example trying to operate on a closed `Connection`, or trying to execute non-DML statements with `executemany()`. `ProgrammingError` is a subclass of `DatabaseError`.

exception `sqlite3.``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 `create_function()`, if the underlying SQLite library does not support deterministic functions. `NotSupportedError` is a subclass of `DatabaseError`.

### SQLite y tipos de Python

SQLite soporta de forma nativa los siguientes tipos: `NULL`, `INTEGER`, `REAL`, `TEXT`, `BLOB`.

Los siguientes tipos de Python se pueden enviar a SQLite sin problema alguno:

Tipo de Python | Tipo de SQLite
--- | ---
`None` | `NULL`
`int` | `INTEGER`
`float` | `REAL`
`str` | `TEXT`
`bytes` | `BLOB`

De esta forma es como los tipos de SQLite son convertidos a tipos de Python por defecto:

Tipo de SQLite | Tipo de Python
--- | ---
`NULL` | `None`
`INTEGER` | `int`
`REAL` | `float`
`TEXT` | depende de `text_factory`, `str` por defecto
`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 adapters, and you can let the `sqlite3` module convert SQLite types to Python types via converters.

## How-to guides

### Using adapters to store custom Python types in SQLite databases

SQLite supports only a limited set of data types natively. To store custom Python types in SQLite databases, adapt them to one of the Python types SQLite natively understands.

There are two ways to adapt Python objects to SQLite types: letting your object adapt itself, or using an adapter callable. The latter will take precedence above the former. For a library that exports a custom type, it may make sense to enable that type to adapt itself. As an application developer, it may make more sense to take direct control by registering custom adapter functions.

#### Permitiéndole al objeto auto adaptarse

Suppose we have a `Point` class that represents a pair of coordinates, `x` and `y`, in a Cartesian coordinate system. The coordinate pair will be stored as a text string in the database, using a semicolon to separate the coordinates. This can be implemented by adding a `__conform__(self, protocol)` method which returns the adapted value. The object passed to protocol will be of type `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])

    con.close()

#### Registrando un adaptador invocable

The other possibility is to create a function that converts the Python object to an SQLite-compatible type. This function can then be registered using `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])

    con.close()

### Convertir valores SQLite a tipos de Python personalizados

Writing an adapter lets you convert from custom Python types to SQLite values. To be able to convert from SQLite values to custom Python types, we use converters.

Regresemos a la clase `Point`. Se almacena las coordenadas x e y de forma separada por punto y coma como una cadena de texto en SQLite.

Primero, se define una función de conversión que acepta la cadena de texto como un parámetro y construye un objeto `Point` de ahí.

Nota

Converter functions are always passed a `bytes` object, no matter the underlying SQLite data type.

    def convert_point(s):
        x, y = map(float, s.split(b";"))
        return Point(x, y)

We now need to tell `sqlite3` when it should convert a given SQLite value. This is done when connecting to a database, using the detect_types parameter of `connect()`. There are three options:

- Implicit: set detect_types to `PARSE_DECLTYPES`

- Explicit: set detect_types to `PARSE_COLNAMES`

- Both: set detect_types to `sqlite3.PARSE_DECLTYPES | sqlite3.PARSE_COLNAMES`. Column names take precedence over declared types.

The following example illustrates the implicit and explicit approaches:

    import sqlite3

    class Point:
        def __init__(self, x, y):
            self.x, self.y = x, y

        def __repr__(self):
            return f"Point({self.x}, {self.y})"

    def adapt_point(point):
        return f"{point.x};{point.y}".encode("utf-8")

    def convert_point(s):
        x, y = list(map(float, s.split(b";")))
        return Point(x, y)

    # Register the adapter and converter
    sqlite3.register_adapter(Point, adapt_point)
    sqlite3.register_converter("point", convert_point)

    # 1) Parse using declared types
    p = Point(4.0, -3.2)
    con = sqlite3.connect(":memory:", detect_types=sqlite3.PARSE_DECLTYPES)
    cur = con.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()

    # 2) Parse using column names
    con = sqlite3.connect(":memory:", detect_types=sqlite3.PARSE_COLNAMES)
    cur = con.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()

### Adaptadores y convertidores por defecto

Hay adaptadores por defecto para los tipos date y datetime en el módulo datetime. Éstos serán enviados como fechas/marcas de tiempo ISO a SQLite.

Los convertidores por defecto están registrados bajo el nombre «date» para `datetime.date` y bajo el mismo nombre para «timestamp» para `datetime.datetime`.

De esta forma, se puede usar date/timestamps para Python sin ajuste adicional en la mayoría de los casos. El formato de los adaptadores también es compatible con las funciones experimentales de SQLite date/time.

El siguiente ejemplo demuestra esto.

    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]))

    con.close()

Si un timestamp almacenado en SQLite tiene una parte fraccional mayor a 6 números, este valor será truncado a precisión de microsegundos por el convertidor de timestamp.

Nota

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()`.

### Adapter and converter recipes

This section shows recipes for common adapters and converters.

    import datetime
    import sqlite3

    def adapt_date_iso(val):
        """Adapt datetime.date to ISO 8601 date."""
        return val.isoformat()

    def adapt_datetime_iso(val):
        """Adapt datetime.datetime to timezone-naive ISO 8601 date."""
        return val.isoformat()

    def adapt_datetime_epoch(val)
        """Adapt datetime.datetime to Unix timestamp."""
        return int(val.timestamp())

    sqlite3.register_adapter(datetime.date, adapt_date_iso)
    sqlite3.register_adapter(datetime.datetime, adapt_datetime_iso)
    sqlite3.register_adapter(datetime.datetime, adapt_datetime_epoch)

    def convert_date(val):
        """Convert ISO 8601 date to datetime.date object."""
        return datetime.date.fromisoformat(val)

    def convert_datetime(val):
        """Convert ISO 8601 datetime to datetime.datetime object."""
        return datetime.datetime.fromisoformat(val)

    def convert_timestamp(val):
        """Convert Unix epoch timestamp to datetime.datetime object."""
        return datetime.datetime.fromtimestamp(val)

    sqlite3.register_converter("date", convert_date)
    sqlite3.register_converter("datetime", convert_datetime)
    sqlite3.register_converter("timestamp", convert_timestamp)

### Using connection shortcut methods

Using the `execute()`, `executemany()`, and `executescript()` methods of the `Connection` class, 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

    langs = [
        ("C++", 1985),
        ("Objective-C", 1984),
    ]

    con = sqlite3.connect(":memory:")

    # Create the table
    con.execute("create table lang(name, first_appeared)")

    # Fill the table
    con.executemany("insert into lang(name, first_appeared) values (?, ?)", langs)

    # Print the table contents
    for row in con.execute("select name, first_appeared from lang"):
        print(row)

    print("I just deleted", con.execute("delete from lang").rowcount, "rows")

    # close is not a shortcut method and it's not called automatically,
    # so the connection object should be closed manually
    con.close()

### Accediendo a las columnas por el nombre en lugar del índice

Una característica útil del módulo `sqlite3` es la clase incluida `sqlite3.Row` diseñada para ser usada como una fábrica de filas.

Filas envueltas con esta clase pueden ser accedidas tanto por índice (al igual que tuplas) como por nombre insensible a mayúsculas o minúsculas:

    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"]

    con.close()

### Usando la conexión como un administrador de contexto

A `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 `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.

Nota

The context manager neither implicitly opens a new transaction nor closes the connection.

    import sqlite3

    con = sqlite3.connect(":memory:")
    con.execute("create table lang (id integer primary key, name varchar unique)")

    # Successful, con.commit() is called automatically afterwards
    with con:
        con.execute("insert into lang(name) values (?)", ("Python",))

    # 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 lang(name) values (?)", ("Python",))
    except sqlite3.IntegrityError:
        print("couldn't add Python twice")

    # Connection object used as context manager only commits or rollbacks transactions,
    # so the connection object should be closed manually
    con.close()

### Working with SQLite URIs

Some useful URI tricks include:

- Open a database in read-only mode:

      con = sqlite3.connect("file:template.db?mode=ro", uri=True)

- Do not implicitly create a new database file if it does not already exist; will raise `OperationalError` if unable to create a new 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.execute("create table t(t)")
      con1.execute("insert into t values(28)")
      con1.commit()
      rows = con2.execute("select * from t").fetchall()

More information about this feature, including a list of parameters, can be found in the SQLite URI documentation.

## Explanation

### Transaction control

The `sqlite3` module does not adhere to the transaction handling recommended by PEP 249.

If the connection attribute `isolation_level` is not `None`, new transactions are implicitly opened before `execute()` and `executemany()` executes `INSERT`, `UPDATE`, `DELETE`, or `REPLACE` statements. Use the `commit()` and `rollback()` methods to respectively commit and roll back pending transactions. You can choose the underlying SQLite transaction behaviour — that is, whether and what type of `BEGIN` statements `sqlite3` implicitly executes – via the `isolation_level` attribute.

If `isolation_level` is set to `None`, no transactions are implicitly opened at all. This leaves the underlying SQLite library in autocommit mode, but also allows the user to perform their own transaction handling using explicit SQL statements. The underlying SQLite library autocommit mode can be queried using the `in_transaction` attribute.

The `executescript()` method implicitly commits any pending transaction before execution of the given SQL script, regardless of the value of `isolation_level`.

Distinto en la versión 3.6: `sqlite3` solía realizar commit en transacciones implícitamente antes de sentencias DDL. Este ya no es el caso.