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# engine/__init__.py # Copyright (C) 2005-2021 the SQLAlchemy authors and contributors # <see AUTHORS file> # # This module is part of SQLAlchemy and is released under # the MIT License: http://www.opensource.org/licenses/mit-license.php """SQL connections, SQL execution and high-level DB-API interface. The engine package defines the basic components used to interface DB-API modules with higher-level statement construction, connection-management, execution and result contexts. The primary "entry point" class into this package is the Engine and its public constructor ``create_engine()``. This package includes: base.py Defines interface classes and some implementation classes which comprise the basic components used to interface between a DB-API, constructed and plain-text statements, connections, transactions, and results. default.py Contains default implementations of some of the components defined in base.py. All current database dialects use the classes in default.py as base classes for their own database-specific implementations. strategies.py The mechanics of constructing ``Engine`` objects are represented here. Defines the ``EngineStrategy`` class which represents how to go from arguments specified to the ``create_engine()`` function, to a fully constructed ``Engine``, including initialization of connection pooling, dialects, and specific subclasses of ``Engine``. threadlocal.py The ``TLEngine`` class is defined here, which is a subclass of the generic ``Engine`` and tracks ``Connection`` and ``Transaction`` objects against the identity of the current thread. This allows certain programming patterns based around the concept of a "thread-local connection" to be possible. The ``TLEngine`` is created by using the "threadlocal" engine strategy in conjunction with the ``create_engine()`` function. url.py Defines the ``URL`` class which represents the individual components of a string URL passed to ``create_engine()``. Also defines a basic module-loading strategy for the dialect specifier within a URL. """ from . import strategies from . import util # noqa from .base import Connection # noqa from .base import Engine # noqa from .base import NestedTransaction # noqa from .base import RootTransaction # noqa from .base import Transaction # noqa from .base import TwoPhaseTransaction # noqa from .interfaces import Compiled # noqa from .interfaces import Connectable # noqa from .interfaces import CreateEnginePlugin # noqa from .interfaces import Dialect # noqa from .interfaces import ExceptionContext # noqa from .interfaces import ExecutionContext # noqa from .interfaces import TypeCompiler # noqa from .result import BaseRowProxy # noqa from .result import BufferedColumnResultProxy # noqa from .result import BufferedColumnRow # noqa from .result import BufferedRowResultProxy # noqa from .result import FullyBufferedResultProxy # noqa from .result import ResultProxy # noqa from .result import RowProxy # noqa from .util import connection_memoize # noqa from ..sql import ddl # noqa # backwards compat default_strategy = "plain" def create_engine(*args, **kwargs): """Create a new :class:`_engine.Engine` instance. The standard calling form is to send the :ref:`URL <database_urls>` as the first positional argument, usually a string that indicates database dialect and connection arguments:: engine = create_engine("postgresql://scott:tiger@localhost/test") .. note:: Please review :ref:`database_urls` for general guidelines in composing URL strings. In particular, special characters, such as those often part of passwords, must be URL encoded to be properly parsed. Additional keyword arguments may then follow it which establish various options on the resulting :class:`_engine.Engine` and its underlying :class:`.Dialect` and :class:`_pool.Pool` constructs:: engine = create_engine("mysql://scott:tiger@hostname/dbname", encoding='latin1', echo=True) The string form of the URL is ``dialect[+driver]://user:password@host/dbname[?key=value..]``, where ``dialect`` is a database name such as ``mysql``, ``oracle``, ``postgresql``, etc., and ``driver`` the name of a DBAPI, such as ``psycopg2``, ``pyodbc``, ``cx_oracle``, etc. Alternatively, the URL can be an instance of :class:`~sqlalchemy.engine.url.URL`. ``**kwargs`` takes a wide variety of options which are routed towards their appropriate components. Arguments may be specific to the :class:`_engine.Engine`, the underlying :class:`.Dialect`, as well as the :class:`_pool.Pool`. Specific dialects also accept keyword arguments that are unique to that dialect. Here, we describe the parameters that are common to most :func:`_sa.create_engine()` usage. Once established, the newly resulting :class:`_engine.Engine` will request a connection from the underlying :class:`_pool.Pool` once :meth:`_engine.Engine.connect` is called, or a method which depends on it such as :meth:`_engine.Engine.execute` is invoked. The :class:`_pool.Pool` in turn will establish the first actual DBAPI connection when this request is received. The :func:`_sa.create_engine` call itself does **not** establish any actual DBAPI connections directly. .. seealso:: :doc:`/core/engines` :doc:`/dialects/index` :ref:`connections_toplevel` :param case_sensitive=True: if False, result column names will match in a case-insensitive fashion, that is, ``row['SomeColumn']``. :param connect_args: a dictionary of options which will be passed directly to the DBAPI's ``connect()`` method as additional keyword arguments. See the example at :ref:`custom_dbapi_args`. :param convert_unicode=False: if set to True, causes all :class:`.String` datatypes to act as though the :paramref:`.String.convert_unicode` flag has been set to ``True``, regardless of a setting of ``False`` on an individual :class:`.String` type. This has the effect of causing all :class:`.String` -based columns to accommodate Python Unicode objects directly as though the datatype were the :class:`.Unicode` type. .. deprecated:: 1.3 The :paramref:`_sa.create_engine.convert_unicode` parameter is deprecated and will be removed in a future release. All modern DBAPIs now support Python Unicode directly and this parameter is unnecessary. :param creator: a callable which returns a DBAPI connection. This creation function will be passed to the underlying connection pool and will be used to create all new database connections. Usage of this function causes connection parameters specified in the URL argument to be bypassed. This hook is not as flexible as the newer :class:`_events.DialectEvents.do_connect` hook which allows complete control over how a connection is made to the database, given the full set of URL arguments and state beforehand. .. seealso:: :class:`_events.DialectEvents.do_connect` - event hook that allows full control over DBAPI connection mechanics. :ref:`custom_dbapi_args` :param echo=False: if True, the Engine will log all statements as well as a ``repr()`` of their parameter lists to the default log handler, which defaults to ``sys.stdout`` for output. If set to the string ``"debug"``, result rows will be printed to the standard output as well. The ``echo`` attribute of ``Engine`` can be modified at any time to turn logging on and off; direct control of logging is also available using the standard Python ``logging`` module. .. seealso:: :ref:`dbengine_logging` - further detail on how to configure logging. :param echo_pool=False: if True, the connection pool will log informational output such as when connections are invalidated as well as when connections are recycled to the default log handler, which defaults to ``sys.stdout`` for output. If set to the string ``"debug"``, the logging will include pool checkouts and checkins. Direct control of logging is also available using the standard Python ``logging`` module. .. seealso:: :ref:`dbengine_logging` - further detail on how to configure logging. :param empty_in_strategy: The SQL compilation strategy to use when rendering an IN or NOT IN expression for :meth:`.ColumnOperators.in_` where the right-hand side is an empty set. This is a string value that may be one of ``static``, ``dynamic``, or ``dynamic_warn``. The ``static`` strategy is the default, and an IN comparison to an empty set will generate a simple false expression "1 != 1". The ``dynamic`` strategy behaves like that of SQLAlchemy 1.1 and earlier, emitting a false expression of the form "expr != expr", which has the effect of evaluting to NULL in the case of a null expression. ``dynamic_warn`` is the same as ``dynamic``, however also emits a warning when an empty set is encountered; this because the "dynamic" comparison is typically poorly performing on most databases. .. versionadded:: 1.2 Added the ``empty_in_strategy`` setting and additionally defaulted the behavior for empty-set IN comparisons to a static boolean expression. :param encoding: Defaults to ``utf-8``. This is the string encoding used by SQLAlchemy for string encode/decode operations which occur within SQLAlchemy, **outside of the DBAPIs own encoding facilities.** .. note:: The ``encoding`` parameter deals only with in-Python encoding issues that were prevalent with many DBAPIs under Python 2. Under Python 3 it is mostly unused. For DBAPIs that require client encoding configurations, such as those of MySQL and Oracle, please consult specific :ref:`dialect documentation <dialect_toplevel>` for details. All modern DBAPIs that work in Python 3 necessarily feature direct support for Python unicode strings. Under Python 2, this was not always the case. For those scenarios where the DBAPI is detected as not supporting a Python ``unicode`` object under Python 2, this encoding is used to determine the source/destination encoding. It is **not used** for those cases where the DBAPI handles unicode directly. To properly configure a system to accommodate Python ``unicode`` objects, the DBAPI should be configured to handle unicode to the greatest degree as is appropriate - see the notes on unicode pertaining to the specific target database in use at :ref:`dialect_toplevel`. Areas where string encoding may need to be accommodated outside of the DBAPI, nearly always under **Python 2 only**, include zero or more of: * the values passed to bound parameters, corresponding to the :class:`.Unicode` type or the :class:`.String` type when ``convert_unicode`` is ``True``; * the values returned in result set columns corresponding to the :class:`.Unicode` type or the :class:`.String` type when ``convert_unicode`` is ``True``; * the string SQL statement passed to the DBAPI's ``cursor.execute()`` method; * the string names of the keys in the bound parameter dictionary passed to the DBAPI's ``cursor.execute()`` as well as ``cursor.setinputsizes()`` methods; * the string column names retrieved from the DBAPI's ``cursor.description`` attribute. When using Python 3, the DBAPI is required to support all of the above values as Python ``unicode`` objects, which in Python 3 are just known as ``str``. In Python 2, the DBAPI does not specify unicode behavior at all, so SQLAlchemy must make decisions for each of the above values on a per-DBAPI basis - implementations are completely inconsistent in their behavior. :param execution_options: Dictionary execution options which will be applied to all connections. See :meth:`~sqlalchemy.engine.Connection.execution_options` :param hide_parameters: Boolean, when set to True, SQL statement parameters will not be displayed in INFO logging nor will they be formatted into the string representation of :class:`.StatementError` objects. .. versionadded:: 1.3.8 .. seealso:: :ref:`dbengine_logging` - further detail on how to configure logging. :param implicit_returning=True: When ``True``, a RETURNING- compatible construct, if available, will be used to fetch newly generated primary key values when a single row INSERT statement is emitted with no existing returning() clause. This applies to those backends which support RETURNING or a compatible construct, including PostgreSQL, Firebird, Oracle, Microsoft SQL Server. Set this to ``False`` to disable the automatic usage of RETURNING. :param isolation_level: this string parameter is interpreted by various dialects in order to affect the transaction isolation level of the database connection. The parameter essentially accepts some subset of these string arguments: ``"SERIALIZABLE"``, ``"REPEATABLE READ"``, ``"READ COMMITTED"``, ``"READ UNCOMMITTED"`` and ``"AUTOCOMMIT"``. Behavior here varies per backend, and individual dialects should be consulted directly. Note that the isolation level can also be set on a per-:class:`_engine.Connection` basis as well, using the :paramref:`.Connection.execution_options.isolation_level` feature. .. seealso:: :attr:`_engine.Connection.default_isolation_level` - view default level :paramref:`.Connection.execution_options.isolation_level` - set per :class:`_engine.Connection` isolation level :ref:`SQLite Transaction Isolation <sqlite_isolation_level>` :ref:`PostgreSQL Transaction Isolation <postgresql_isolation_level>` :ref:`MySQL Transaction Isolation <mysql_isolation_level>` :ref:`session_transaction_isolation` - for the ORM :param json_deserializer: for dialects that support the :class:`_types.JSON` datatype, this is a Python callable that will convert a JSON string to a Python object. By default, the Python ``json.loads`` function is used. .. versionchanged:: 1.3.7 The SQLite dialect renamed this from ``_json_deserializer``. :param json_serializer: for dialects that support the :class:`_types.JSON` datatype, this is a Python callable that will render a given object as JSON. By default, the Python ``json.dumps`` function is used. .. versionchanged:: 1.3.7 The SQLite dialect renamed this from ``_json_serializer``. :param label_length=None: optional integer value which limits the size of dynamically generated column labels to that many characters. If less than 6, labels are generated as "_(counter)". If ``None``, the value of ``dialect.max_identifier_length``, which may be affected via the :paramref:`_sa.create_engine.max_identifier_length` parameter, is used instead. The value of :paramref:`_sa.create_engine.label_length` may not be larger than that of :paramref:`_sa.create_engine.max_identfier_length`. .. seealso:: :paramref:`_sa.create_engine.max_identifier_length` :param listeners: A list of one or more :class:`~sqlalchemy.interfaces.PoolListener` objects which will receive connection pool events. :param logging_name: String identifier which will be used within the "name" field of logging records generated within the "sqlalchemy.engine" logger. Defaults to a hexstring of the object's id. .. seealso:: :ref:`dbengine_logging` - further detail on how to configure logging. :param max_identifier_length: integer; override the max_identifier_length determined by the dialect. if ``None`` or zero, has no effect. This is the database's configured maximum number of characters that may be used in a SQL identifier such as a table name, column name, or label name. All dialects determine this value automatically, however in the case of a new database version for which this value has changed but SQLAlchemy's dialect has not been adjusted, the value may be passed here. .. versionadded:: 1.3.9 .. seealso:: :paramref:`_sa.create_engine.label_length` :param max_overflow=10: the number of connections to allow in connection pool "overflow", that is connections that can be opened above and beyond the pool_size setting, which defaults to five. this is only used with :class:`~sqlalchemy.pool.QueuePool`. :param module=None: reference to a Python module object (the module itself, not its string name). Specifies an alternate DBAPI module to be used by the engine's dialect. Each sub-dialect references a specific DBAPI which will be imported before first connect. This parameter causes the import to be bypassed, and the given module to be used instead. Can be used for testing of DBAPIs as well as to inject "mock" DBAPI implementations into the :class:`_engine.Engine`. :param paramstyle=None: The `paramstyle <http://legacy.python.org/dev/peps/pep-0249/#paramstyle>`_ to use when rendering bound parameters. This style defaults to the one recommended by the DBAPI itself, which is retrieved from the ``.paramstyle`` attribute of the DBAPI. However, most DBAPIs accept more than one paramstyle, and in particular it may be desirable to change a "named" paramstyle into a "positional" one, or vice versa. When this attribute is passed, it should be one of the values ``"qmark"``, ``"numeric"``, ``"named"``, ``"format"`` or ``"pyformat"``, and should correspond to a parameter style known to be supported by the DBAPI in use. :param pool=None: an already-constructed instance of :class:`~sqlalchemy.pool.Pool`, such as a :class:`~sqlalchemy.pool.QueuePool` instance. If non-None, this pool will be used directly as the underlying connection pool for the engine, bypassing whatever connection parameters are present in the URL argument. For information on constructing connection pools manually, see :ref:`pooling_toplevel`. :param poolclass=None: a :class:`~sqlalchemy.pool.Pool` subclass, which will be used to create a connection pool instance using the connection parameters given in the URL. Note this differs from ``pool`` in that you don't actually instantiate the pool in this case, you just indicate what type of pool to be used. :param pool_logging_name: String identifier which will be used within the "name" field of logging records generated within the "sqlalchemy.pool" logger. Defaults to a hexstring of the object's id. .. seealso:: :ref:`dbengine_logging` - further detail on how to configure logging. :param pool_pre_ping: boolean, if True will enable the connection pool "pre-ping" feature that tests connections for liveness upon each checkout. .. versionadded:: 1.2 .. seealso:: :ref:`pool_disconnects_pessimistic` :param pool_size=5: the number of connections to keep open inside the connection pool. This used with :class:`~sqlalchemy.pool.QueuePool` as well as :class:`~sqlalchemy.pool.SingletonThreadPool`. With :class:`~sqlalchemy.pool.QueuePool`, a ``pool_size`` setting of 0 indicates no limit; to disable pooling, set ``poolclass`` to :class:`~sqlalchemy.pool.NullPool` instead. :param pool_recycle=-1: this setting causes the pool to recycle connections after the given number of seconds has passed. It defaults to -1, or no timeout. For example, setting to 3600 means connections will be recycled after one hour. Note that MySQL in particular will disconnect automatically if no activity is detected on a connection for eight hours (although this is configurable with the MySQLDB connection itself and the server configuration as well). .. seealso:: :ref:`pool_setting_recycle` :param pool_reset_on_return='rollback': set the :paramref:`_pool.Pool.reset_on_return` parameter of the underlying :class:`_pool.Pool` object, which can be set to the values ``"rollback"``, ``"commit"``, or ``None``. .. seealso:: :paramref:`_pool.Pool.reset_on_return` :param pool_timeout=30: number of seconds to wait before giving up on getting a connection from the pool. This is only used with :class:`~sqlalchemy.pool.QueuePool`. :param pool_use_lifo=False: use LIFO (last-in-first-out) when retrieving connections from :class:`.QueuePool` instead of FIFO (first-in-first-out). Using LIFO, a server-side timeout scheme can reduce the number of connections used during non- peak periods of use. When planning for server-side timeouts, ensure that a recycle or pre-ping strategy is in use to gracefully handle stale connections. .. versionadded:: 1.3 .. seealso:: :ref:`pool_use_lifo` :ref:`pool_disconnects` :param plugins: string list of plugin names to load. See :class:`.CreateEnginePlugin` for background. .. versionadded:: 1.2.3 :param strategy='plain': selects alternate engine implementations. Currently available are: * the ``threadlocal`` strategy, which is described in :ref:`threadlocal_strategy`; * the ``mock`` strategy, which dispatches all statement execution to a function passed as the argument ``executor``. See `example in the FAQ <http://docs.sqlalchemy.org/en/latest/faq/metadata_schema.html#how-can-i-get-the-create-table-drop-table-output-as-a-string>`_. :param executor=None: a function taking arguments ``(sql, *multiparams, **params)``, to which the ``mock`` strategy will dispatch all statement execution. Used only by ``strategy='mock'``. """ # noqa strategy = kwargs.pop("strategy", default_strategy) strategy = strategies.strategies[strategy] return strategy.create(*args, **kwargs) def engine_from_config(configuration, prefix="sqlalchemy.", **kwargs): """Create a new Engine instance using a configuration dictionary. The dictionary is typically produced from a config file. The keys of interest to ``engine_from_config()`` should be prefixed, e.g. ``sqlalchemy.url``, ``sqlalchemy.echo``, etc. The 'prefix' argument indicates the prefix to be searched for. Each matching key (after the prefix is stripped) is treated as though it were the corresponding keyword argument to a :func:`_sa.create_engine` call. The only required key is (assuming the default prefix) ``sqlalchemy.url``, which provides the :ref:`database URL <database_urls>`. A select set of keyword arguments will be "coerced" to their expected type based on string values. The set of arguments is extensible per-dialect using the ``engine_config_types`` accessor. :param configuration: A dictionary (typically produced from a config file, but this is not a requirement). Items whose keys start with the value of 'prefix' will have that prefix stripped, and will then be passed to :ref:`create_engine`. :param prefix: Prefix to match and then strip from keys in 'configuration'. :param kwargs: Each keyword argument to ``engine_from_config()`` itself overrides the corresponding item taken from the 'configuration' dictionary. Keyword arguments should *not* be prefixed. """ options = dict( (key[len(prefix) :], configuration[key]) for key in configuration if key.startswith(prefix) ) options["_coerce_config"] = True options.update(kwargs) url = options.pop("url") return create_engine(url, **options) __all__ = ("create_engine", "engine_from_config")