"sqlite3" --- SQLite 数据库 DB-API 2.0 接口模块
***********************************************

**原始碼：**Lib/sqlite3/

SQLite 是一个C语言库，它可以提供一种轻量级的基于磁盘的数据库，这种数据
库不需要独立的服务器进程，也允许需要使用一种非标准的 SQL 查询语言来访
问它。一些应用程序可以使用 SQLite 作为内部数据存储。可以用它来创建一个
应用程序原型，然后再迁移到更大的数据库，比如 PostgreSQL 或 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:

* 教程 teaches how to use the "sqlite3" module.

* 参考 describes the classes and functions this module defines.

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

* 解釋 provides in-depth background on transaction control.

也參考:

  https://www.sqlite.org
     SQLite的主页；它的文档详细描述了它所支持的 SQL 方言的语法和可用的
     数据类型。

  https://www.w3schools.com/sql/
     学习 SQL 语法的教程、参考和例子。

  **PEP 249** - DB-API 2.0 规范
     PEP 由 Marc-André Lemburg 撰寫。


教程
====

In this tutorial, you will create a database of Monty Python movies
using basic "sqlite3" functionality. It assumes a fundamental
understanding of database concepts, including cursors and
transactions.

First, we need to create a new database and open a database connection
to allow "sqlite3" to work with it. Call "sqlite3.connect()" to create
a connection to the database "tutorial.db" in the current working
directory, implicitly creating it if it does not exist:

   import sqlite3
   con = sqlite3.connect("tutorial.db")

The returned "Connection" object "con" represents the connection to
the on-disk database.

In order to execute SQL statements and fetch results from SQL queries,
we will need to use a database cursor. Call "con.cursor()" to create
the "Cursor":

   cur = con.cursor()

Now that we've got a database connection and a cursor, we can create a
database table "movie" with columns for title, release year, and
review score. For simplicity, we can just use column names in the
table declaration -- thanks to the flexible typing feature of SQLite,
specifying the data types is optional. Execute the "CREATE TABLE"
statement by calling "cur.execute(...)":

   cur.execute("CREATE TABLE movie(title, year, score)")

We can verify that the new table has been created by querying the
"sqlite_master" table built-in to SQLite, which should now contain an
entry for the "movie" table definition (see The Schema Table for
details). Execute that query by calling "cur.execute(...)", assign the
result to "res", and call "res.fetchone()" to fetch the resulting row:

   >>> res = cur.execute("SELECT name FROM sqlite_master")
   >>> res.fetchone()
   ('movie',)

We can see that the table has been created, as the query returns a
"tuple" containing the table's name. If we query "sqlite_master" for a
non-existent table "spam", "res.fetchone()" will return "None":

   >>> res = cur.execute("SELECT name FROM sqlite_master WHERE name='spam'")
   >>> res.fetchone() is None
   True

Now, add two rows of data supplied as SQL literals by executing an
"INSERT" statement, once again by calling "cur.execute(...)":

   cur.execute("""
       INSERT INTO movie VALUES
           ('Monty Python and the Holy Grail', 1975, 8.2),
           ('And Now for Something Completely Different', 1971, 7.5)
   """)

The "INSERT" statement implicitly opens a transaction, which needs to
be committed before changes are saved in the database (see Transaction
control for details). Call "con.commit()" on the connection object to
commit the transaction:

   con.commit()

We can verify that the data was inserted correctly by executing a
"SELECT" query. Use the now-familiar "cur.execute(...)" to assign the
result to "res", and call "res.fetchall()" to return all resulting
rows:

   >>> res = cur.execute("SELECT score FROM movie")
   >>> res.fetchall()
   [(8.2,), (7.5,)]

The result is a "list" of two "tuple"s, one per row, each containing
that row's "score" value.

Now, insert three more rows by calling "cur.executemany(...)":

   data = [
       ("Monty Python Live at the Hollywood Bowl", 1982, 7.9),
       ("Monty Python's The Meaning of Life", 1983, 7.5),
       ("Monty Python's Life of Brian", 1979, 8.0),
   ]
   cur.executemany("INSERT INTO movie VALUES(?, ?, ?)", data)
   con.commit()  # Remember to commit the transaction after executing INSERT.

Notice that "?" placeholders are used to bind "data" to the query.
Always use placeholders instead of string formatting to bind Python
values to SQL statements, to avoid SQL injection attacks (see How to
use placeholders to bind values in SQL queries for more details).

We can verify that the new rows were inserted by executing a "SELECT"
query, this time iterating over the results of the query:

   >>> for row in cur.execute("SELECT year, title FROM movie ORDER BY year"):
   ...     print(row)
   (1971, 'And Now for Something Completely Different')
   (1975, 'Monty Python and the Holy Grail')
   (1979, "Monty Python's Life of Brian")
   (1982, 'Monty Python Live at the Hollywood Bowl')
   (1983, "Monty Python's The Meaning of Life")

Each row is a two-item "tuple" of "(year, title)", matching the
columns selected in the query.

Finally, verify that the database has been written to disk by calling
"con.close()" to close the existing connection, opening a new one,
creating a new cursor, then querying the database:

   >>> con.close()
   >>> new_con = sqlite3.connect("tutorial.db")
   >>> new_cur = new_con.cursor()
   >>> res = new_cur.execute("SELECT title, year FROM movie ORDER BY score DESC")
   >>> title, year = res.fetchone()
   >>> print(f'The highest scoring Monty Python movie is {title!r}, released in {year}')
   The highest scoring Monty Python movie is 'Monty Python and the Holy Grail', released in 1975

You've now created an SQLite database using the "sqlite3" module,
inserted data and retrieved values from it in multiple ways.

也參考:

  * How-to guides for further reading:

       * How to use placeholders to bind values in SQL queries

       * How to adapt custom Python types to SQLite values

       * How to convert SQLite values to custom Python types

       * How to use the connection context manager

       * How to create and use row factories

  * 解釋 for in-depth background on transaction control.


参考
====


Module functions
----------------

sqlite3.connect(database, timeout=5.0, detect_types=0, isolation_level='DEFERRED', check_same_thread=True, factory=sqlite3.Connection, cached_statements=100, uri=False)

   Open a connection to an SQLite database.

   參數:
      * **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 "OperationalError" when a table
        is locked. If another connection opens a transaction to modify
        a table, that table will be locked until the 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),
        "ProgrammingError" will be raised if the database connection
        is used by a thread other than the one that created it. If
        "False", the connection may be accessed in multiple threads;
        write operations may need to be serialized by the user to
        avoid data corruption. See "threadsafety" for more
        information.

      * **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 (Uniform Resource Identifier) 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
        How to work with SQLite URIs.

   傳回型態:
      Connection

   引发一个 审计事件 "sqlite3.connect"，附带参数 "database"。

   引发一个 审计事件 "sqlite3.connect/handle"，附带参数
   "connection_handle"。

   3.4 版新加入: *uri* 參數。

   3.7 版更變: *database* 现在可以是一个 *path-like object* 对象了，不
   仅仅是字符串。

   3.10 版新加入: The "sqlite3.connect/handle" auditing event.

sqlite3.complete_statement(statement)

   Return "True" if the string *statement* appears to contain one or
   more complete SQL statements. No syntactic verification or parsing
   of any kind is performed, other than checking that there are no
   unclosed string literals and the statement is terminated by a
   semicolon.

   範例：

      >>> sqlite3.complete_statement("SELECT foo FROM bar;")
      True
      >>> sqlite3.complete_statement("SELECT foo")
      False

   This function may be useful during command-line input to determine
   if the entered text seems to form a complete SQL statement, or if
   additional input is needed before calling "execute()".

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.

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.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.


Module constants
----------------

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.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.SQLITE_OK
sqlite3.SQLITE_DENY
sqlite3.SQLITE_IGNORE

   Flags that should be returned by the *authorizer_callback* callable
   passed to "Connection.set_authorizer()", to indicate whether:

   * Access is allowed ("SQLITE_OK"),

   * The SQL statement should be aborted with an error ("SQLITE_DENY")

   * The column should be treated as a "NULL" value ("SQLITE_IGNORE")

sqlite3.apilevel

   指明所支持的 DB-API 级别的字符串常量。 根据 DB-API 的需要设置。 硬
   编码为 ""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"".

   備註:

     The "named" DB-API parameter style is also supported.

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()

   注意 SQLITE_THREADSAFE 级别 与 DB-API 2.0 "threadsafety" 级别不一致
   。

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.


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.

   也參考:

     * How to use connection shortcut methods

     * How to use the connection context manager

   SQLite 数据库连接对象有如下的属性和方法：

   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=(), /)

      创建一个新的 "Cursor" 对象，并在其上使用给出的 *sql* 和
      *parameters* 调用 "execute()"。 返回新的游标对象。

   executemany(sql, parameters, /)

      创建一个新的 "Cursor" 对象，并在其上使用给出的 *sql* 和
      *parameters* 调用 "executemany()"。 返回新的游标对象。

   executescript(sql_script, /)

      创建一个新的 "Cursor" 对象，并在其上使用给出的 *sql_script* 调用
      "executescript()"。 返回新的游标对象。

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

      Create or remove a user-defined SQL function.

      參數:
         * **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.

      丟出:
         **NotSupportedError** -- If *deterministic* is used with
         SQLite versions older than 3.8.3.

      3.8 版新加入: 新增 *deterministic* 參數。

      範例：

         >>> import hashlib
         >>> def md5sum(t):
         ...     return hashlib.md5(t).hexdigest()
         >>> con = sqlite3.connect(":memory:")
         >>> con.create_function("md5", 1, md5sum)
         >>> for row in con.execute("SELECT md5(?)", (b"foo",)):
         ...     print(row)
         ('acbd18db4cc2f85cedef654fccc4a4d8',)

   create_aggregate(name, /, n_arg, aggregate_class)

      Create or remove a user-defined SQL aggregate function.

      參數:
         * **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.

      範例：

         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.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)

      使用排序函数 *callable* 创建一个名为 *name* 的排序规则。
      *callable* 被传递给两个 "字符串" 参数，并且它应该返回一个 "整数"
      。

      * 如果前者的排序高于后者则为 "1"

      * 如果前者的排序低于于后者则为 "-1"

      * 如果它们的顺序相同则为 "0"

      下面的例子显示了一个反向排序的排序方法:

         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.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 "OperationalError".

   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 one of "SQLITE_OK", "SQLITE_DENY", or
      "SQLITE_IGNORE" to signal how access to the column should be
      handled by the underlying SQLite library.

      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(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*.

      从处理函数返回非零值将终止当前正在执行的查询并导致它引发
      "OperationalError" 异常。

   set_trace_callback(trace_callback)

      Register callable *trace_callback* to be invoked 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 of the "sqlite3" module and the
      execution of triggers defined in the current database.

      Passing "None" as *trace_callback* will disable the trace
      callback.

      備註:

        在跟踪回调中产生的异常不会被传播。作为开发和调试的辅助手段，使
        用 "enable_callback_tracebacks()" 来启用打印跟踪回调中产生的异
        常的回调。

      3.3 版新加入.

   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.

      備註:

        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**.

      引发一个 审计事件 "sqlite3.enable_load_extension"，附带参数
      "connection", "enabled"。

      3.2 版新加入.

      3.10 版更變: 增加了 "sqlite3.enable_load_extension" 审计事件。

         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.

      引发一个 审计事件 "sqlite3.load_extension"，附带参数
      "connection", "path"。

      3.2 版新加入.

      3.10 版更變: 增加了 "sqlite3.load_extension" 审计事件。

   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.

      範例：

         # Convert file example.db to SQL dump file dump.sql
         con = sqlite3.connect('example.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.

      參數:
         * **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
           statement.

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

      Example 1, copy an existing database into another:

         def progress(status, remaining, total):
             print(f'Copied {total-remaining} of {total} pages...')

         src = sqlite3.connect('example.db')
         dst = sqlite3.connect('backup.db')
         with dst:
             src.backup(dst, pages=1, progress=progress)
         dst.close()
         src.close()

      Example 2, copy an existing database into a transient copy:

         src = sqlite3.connect('example.db')
         dst = sqlite3.connect(':memory:')
         src.backup(dst)

      3.7 版新加入.

   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.

      3.2 版新加入.

   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"".

   row_factory

      The initial "row_factory" for "Cursor" objects created from this
      connection. Assigning to this attribute does not affect the
      "row_factory" of existing cursors belonging to this connection,
      only new ones. Is "None" by default, meaning each row is
      returned as a "tuple".

      See How to create and use row factories for more details.

   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".

      範例：

         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.


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 t FROM data"):
          print(row)

class sqlite3.Cursor

   "Cursor" 游标实例具有以下属性和方法。

   execute(sql, parameters=(), /)

      Execute SQL a single SQL statement, optionally binding Python
      values using placeholders.

      參數:
         * **sql** (*str*) -- A single SQL statement.

         * **parameters** ("dict" | *sequence*) -- Python values to
           bind to placeholders in *sql*. A "dict" if named
           placeholders are used. A *sequence* if unnamed placeholders
           are used. See How to use placeholders to bind values in SQL
           queries.

      丟出:
         **Warning** -- If *sql* contains more than one SQL statement.

      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*.

      Use "executescript()" to execute multiple SQL statements.

   executemany(sql, parameters, /)

      For every item in *parameters*, repeatedly execute the
      parameterized SQL statement *sql*.

      Uses the same implicit transaction handling as "execute()".

      參數:
         * **sql** (*str*) -- A single SQL DML (Data Manipulation
           Language) statement.

         * **parameters** (*iterable*) -- An *iterable* of parameters
           to bind with the placeholders in *sql*. See How to use
           placeholders to bind values in SQL queries.

      丟出:
         * **ProgrammingError** -- If *sql* is not a DML statment.

         * **Warning** -- If *sql* contains more than one SQL
           statement.

      範例：

         rows = [
             ("row1",),
             ("row2",),
         ]
         # cur is an sqlite3.Cursor object
         cur.executemany("INSERT INTO data VALUES(?)", rows)

   executescript(sql_script, /)

      Execute the SQL statements in *sql_script*. If there is a
      pending transaction, 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".

      範例：

         # 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()

      If "row_factory" is "None", return the next row query result set
      as a "tuple". Else, pass it to the row factory and return its
      result. Return "None" if no more data is available.

   fetchmany(size=cursor.arraysize)

      Return 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.

      请注意 *size* 形参会涉及到性能方面的考虑。为了获得优化的性能，通
      常最好是使用 arraysize 属性。 如果使用 *size* 形参，则最好在从一
      个 "fetchmany()" 调用到下一个调用之间保持相同的值。

   fetchall()

      Return 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()

      立即关闭 cursor（而不是在当 "__del__" 被调用的时候）。

      从这一时刻起该 cursor 将不再可用，如果再尝试用该 cursor 执行任何
      操作将引发 "ProgrammingError" 异常。

   setinputsizes(sizes, /)

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

   setoutputsize(size, column=None, /)

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

   arraysize

      用于控制 "fetchmany()" 返回行数的可读取/写入属性。 该属性的默认
      值为 1，表示每次调用将获取单独一行。

   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

   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".

      对于没有任何匹配行的 "SELECT" 语句同样会设置该属性。

   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".

      備註:

        对 "WITHOUT ROWID" 表的插入不被记录。

      3.6 版更變: 新增 "REPLACE" 陳述式的支援。

   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 (Common Table
      Expression) queries. It is only updated by the "execute()" and
      "executemany()" methods.

   row_factory

      Control how a row fetched from this "Cursor" is represented. If
      "None", a row is represented as a "tuple". Can be set to the
      included "sqlite3.Row"; or a *callable* that accepts two
      arguments, a "Cursor" object and the "tuple" of row values, and
      returns a custom object representing an SQLite row.

      Defaults to what "Connection.row_factory" was set to when the
      "Cursor" was created. Assigning to this attribute does not
      affect "Connection.row_factory" of the parent connection.

      See How to create and use row factories for more details.


Row objects
-----------

class sqlite3.Row

   A "Row" instance serves as a highly optimized "row_factory" for
   "Connection" objects. It supports iteration, equality testing,
   "len()", and *mapping* access by column name and index.

   Two "Row" objects compare equal if they have identical column names
   and values.

   See How to create and use row factories for more details.

   keys()

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

   3.5 版更變: 添加了对切片操作的支持。


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.


例外
----

异常层次是由 DB-API 2.0 (**PEP 249**) 定义的。

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

   本模块中其他异常的基类。使用它来捕捉所有的错误，只需一条 "except"
   语句。 "Error" 是 "Exception" 的子类。

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

   对与数据库有关的错误引发的异常。它作为几种数据库错误的基础异常。它
   只通过专门的子类隐式引发。 "DatabaseError" 是 "Error" 的一个子类。

exception sqlite3.DataError

   由于处理的数据有问题而产生的异常，比如数字值超出范围，字符串太长。
   "DataError" 是 "DatabaseError" 的子类。

exception sqlite3.OperationalError

   与数据库操作有关的错误而引发的异常，不一定在程序员的控制之下。例如
   ，数据库路径没有找到，或者一个事务无法被处理。 "OperationalError"
   是 "DatabaseError" 的子类。

exception sqlite3.IntegrityError

   当数据库的关系一致性受到影响时引发的异常。 例如外键检查失败等。 它
   是 "DatabaseError" 的子类。

exception sqlite3.InternalError

   当 SQLite 遇到一个内部错误时引发的异常。如果它被引发，可能表明运行
   中的 SQLite 库有问题。  "InternalError" 是 "DatabaseError" 的子类。

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 与 Python 类型
---------------------

SQLite 原生支持如下的类型： "NULL"，"INTEGER"，"REAL"，"TEXT"，"BLOB"
。

因此可以将以下Python类型发送到SQLite而不会出现任何问题：

+---------------------------------+---------------+
| Python 类型                     | SQLite 类型   |
|=================================|===============|
| "None"                          | "NULL"        |
+---------------------------------+---------------+
| "int"                           | "INTEGER"     |
+---------------------------------+---------------+
| "float"                         | "REAL"        |
+---------------------------------+---------------+
| "str"                           | "TEXT"        |
+---------------------------------+---------------+
| "bytes"                         | "BLOB"        |
+---------------------------------+---------------+

这是SQLite类型默认转换为Python类型的方式：

+---------------+------------------------------------------------+
| SQLite 类型   | Python 类型                                    |
|===============|================================================|
| "NULL"        | "None"                                         |
+---------------+------------------------------------------------+
| "INTEGER"     | "int"                                          |
+---------------+------------------------------------------------+
| "REAL"        | "float"                                        |
+---------------+------------------------------------------------+
| "TEXT"        | 取决于 "text_factory" , 默认为 "str"           |
+---------------+------------------------------------------------+
| "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.


默认适配器和转换器
------------------

对于 datetime 模块中的 date 和 datetime 类型已提供了默认的适配器。 它
们将会以 ISO 日期/ISO 时间戳的形式发给 SQLite。

默认转换器使用的注册名称是针对 "datetime.date" 的 "date" 和针对
"datetime.datetime" 的 "timestamp"。

通过这种方式，你可以在大多数情况下使用 Python 的 date/timestamp 对象而
无须任何额外处理。 适配器的格式还与实验性的 SQLite date/time 函数兼容
。

下面的示例演示了这一点。

   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()

如果存储在 SQLite 中的时间戳的小数位多于 6 个数字，则时间戳转换器会将
该值截断至微秒精度。

備註:

  默认的 "时间戳" 转换器忽略了数据库中的 UTC 偏移，总是返回一个原生的
  "datetime.datetime" 对象。要在时间戳中保留 UTC 偏移，可以不使用转换
  器，或者用 "register_converter()" 注册一个偏移感知的转换器。


How-to guides
=============


How to use placeholders to bind values in SQL queries
-----------------------------------------------------

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. For example,
an attacker can simply close the single quote and inject "OR TRUE" to
select all rows:

   >>> # Never do this -- insecure!
   >>> symbol = input()
   ' OR TRUE; --
   >>> sql = "SELECT * FROM stocks WHERE symbol = '%s'" % symbol
   >>> print(sql)
   SELECT * FROM stocks WHERE symbol = '' OR TRUE; --'
   >>> cur.execute(sql)

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* whose length must match the
number of placeholders, or a "ProgrammingError" is raised. For the
named style, *parameters* should be an instance of a "dict" (or a
subclass), which must contain keys for all named parameters; any extra
items are ignored. Here's an example of both styles:

   con = sqlite3.connect(":memory:")
   cur = con.execute("CREATE TABLE lang(name, first_appeared)")

   # This is the named style used with executemany():
   data = (
       {"name": "C", "year": 1972},
       {"name": "Fortran", "year": 1957},
       {"name": "Python", "year": 1991},
       {"name": "Go", "year": 2009},
   )
   cur.executemany("INSERT INTO lang VALUES(:name, :year)", data)

   # This is the qmark style used in a SELECT query:
   params = (1972,)
   cur.execute("SELECT * FROM lang WHERE first_appeared = ?", params)
   print(cur.fetchall())

備註:

  **PEP 249** numeric placeholders are *not* supported. If used, they
  will be interpreted as named placeholders.


How to adapt custom Python types to SQLite values
-------------------------------------------------

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.


How to write adaptable objects
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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".

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

       def __conform__(self, protocol):
           if protocol is sqlite3.PrepareProtocol:
               return f"{self.x};{self.y}"

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

   cur.execute("SELECT ?", (Point(4.0, -3.2),))
   print(cur.fetchone()[0])


How to register adapter callables
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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()".

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

   def adapt_point(point):
       return f"{point.x};{point.y}"

   sqlite3.register_adapter(Point, adapt_point)

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

   cur.execute("SELECT ?", (Point(1.0, 2.5),))
   print(cur.fetchone()[0])


How to convert SQLite values to custom Python types
---------------------------------------------------

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*.

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.

備註:

  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:

   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}"

   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])


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.decode())

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

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

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


How to use 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.

   # Create and fill the table.
   con = sqlite3.connect(":memory:")
   con.execute("CREATE TABLE lang(name, first_appeared)")
   data = [
       ("C++", 1985),
       ("Objective-C", 1984),
   ]
   con.executemany("INSERT INTO lang(name, first_appeared) VALUES(?, ?)", data)

   # 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;
   # the connection object should be closed manually
   con.close()


How to use the connection context manager
-----------------------------------------

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.

備註:

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

   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()


How to work with SQLite URIs
----------------------------

Some useful URI tricks include:

* Open a database in read-only mode:

   >>> con = sqlite3.connect("file:tutorial.db?mode=ro", uri=True)
   >>> con.execute("CREATE TABLE readonly(data)")
   Traceback (most recent call last):
   OperationalError: attempt to write a readonly database

* 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)
   Traceback (most recent call last):
   OperationalError: unable to open database file

* Create a shared named in-memory database:

   db = "file:mem1?mode=memory&cache=shared"
   con1 = sqlite3.connect(db, uri=True)
   con2 = sqlite3.connect(db, uri=True)
   with con1:
       con1.execute("CREATE TABLE shared(data)")
       con1.execute("INSERT INTO shared VALUES(28)")
   res = con2.execute("SELECT data FROM shared")
   assert res.fetchone() == (28,)

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


How to create and use row factories
-----------------------------------

By default, "sqlite3" represents each row as a "tuple". If a "tuple"
does not suit your needs, you can use the "sqlite3.Row" class or a
custom "row_factory".

While "row_factory" exists as an attribute both on the "Cursor" and
the "Connection", it is recommended to set "Connection.row_factory",
so all cursors created from the connection will use the same row
factory.

"Row" provides indexed and case-insensitive named access to columns,
with minimal memory overhead and performance impact over a "tuple". To
use "Row" as a row factory, assign it to the "row_factory" attribute:

   >>> con = sqlite3.connect(":memory:")
   >>> con.row_factory = sqlite3.Row

Queries now return "Row" objects:

   >>> res = con.execute("SELECT 'Earth' AS name, 6378 AS radius")
   >>> row = res.fetchone()
   >>> row.keys()
   ['name', 'radius']
   >>> row[0]         # Access by index.
   'Earth'
   >>> row["name"]    # Access by name.
   'Earth'
   >>> row["RADIUS"]  # Column names are case-insensitive.
   6378

You can create a custom "row_factory" that returns each row as a
"dict", with column names mapped to values:

   def dict_factory(cursor, row):
       fields = [column[0] for column in cursor.description]
       return {key: value for key, value in zip(fields, row)}

Using it, queries now return a "dict" instead of a "tuple":

   >>> con = sqlite3.connect(":memory:")
   >>> con.row_factory = dict_factory
   >>> for row in con.execute("SELECT 1 AS a, 2 AS b"):
   ...     print(row)
   {'a': 1, 'b': 2}

The following row factory returns a *named tuple*:

   from collections import namedtuple

   def namedtuple_factory(cursor, row):
       fields = [column[0] for column in cursor.description]
       cls = namedtuple("Row", fields)
       return cls._make(row)

"namedtuple_factory()" can be used as follows:

   >>> con = sqlite3.connect(":memory:")
   >>> con.row_factory = namedtuple_factory
   >>> cur = con.execute("SELECT 1 AS a, 2 AS b")
   >>> row = cur.fetchone()
   >>> row
   Row(a=1, b=2)
   >>> row[0]  # Indexed access.
   1
   >>> row.b   # Attribute access.
   2

With some adjustments, the above recipe can be adapted to use a
"dataclass", or any other custom class, instead of a "namedtuple".


解釋
====


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; for other statements, no implicit transaction handling is
performed. 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".

3.6 版更變: "sqlite3" used to implicitly commit an open transaction
before DDL statements.  This is no longer the case.
