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def create_engine(url: 'Union[str, _url.URL]', **kwargs: 'Any') -> 'Engine'
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+psycopg2://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+mysqldb://scott:tiger@hostname/dbname",
pool_recycle=3600,
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 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 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
:meth:`_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::
:meth:`_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: No longer used; SQLAlchemy now uses
"empty set" behavior for IN in all cases.
:param enable_from_linting: defaults to True. Will emit a warning
if a given SELECT statement is found to have un-linked FROM elements
which would cause a cartesian product.
.. versionadded:: 1.4
.. seealso::
:ref:`change_4737`
:param execution_options: Dictionary execution options which will
be applied to all connections. See
:meth:`~sqlalchemy.engine.Connection.execution_options`
:param future: Use the 2.0 style :class:`_engine.Engine` and
:class:`_engine.Connection` API.
As of SQLAlchemy 2.0, this parameter is present for backwards
compatibility only and must remain at its default value of ``True``.
The :paramref:`_sa.create_engine.future` parameter will be
deprecated in a subsequent 2.x release and eventually removed.
.. versionadded:: 1.4
.. versionchanged:: 2.0 All :class:`_engine.Engine` objects are
"future" style engines and there is no longer a ``future=False``
mode of operation.
.. seealso::
:ref:`migration_20_toplevel`
: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: Legacy parameter that may only be set
to True. In SQLAlchemy 2.0, this parameter does nothing. In order to
disable "implicit returning" for statements invoked by the ORM,
configure this on a per-table basis using the
:paramref:`.Table.implicit_returning` parameter.
:param insertmanyvalues_page_size: number of rows to format into an
INSERT statement when the statement uses "insertmanyvalues" mode, which is
a paged form of bulk insert that is used for many backends when using
:term:`executemany` execution typically in conjunction with RETURNING.
Defaults to 1000, but may also be subject to dialect-specific limiting
factors which may override this value on a per-statement basis.
.. versionadded:: 2.0
.. seealso::
:ref:`engine_insertmanyvalues`
:ref:`engine_insertmanyvalues_page_size`
:paramref:`_engine.Connection.execution_options.insertmanyvalues_page_size`
:param isolation_level: optional string name of an isolation level
which will be set on all new connections unconditionally.
Isolation levels are typically some subset of the string names
``"SERIALIZABLE"``, ``"REPEATABLE READ"``,
``"READ COMMITTED"``, ``"READ UNCOMMITTED"`` and ``"AUTOCOMMIT"``
based on backend.
The :paramref:`_sa.create_engine.isolation_level` parameter is
in contrast to the
:paramref:`.Connection.execution_options.isolation_level`
execution option, which may be set on an individual
:class:`.Connection`, as well as the same parameter passed to
:meth:`.Engine.execution_options`, where it may be used to create
multiple engines with different isolation levels that share a common
connection pool and dialect.
.. versionchanged:: 2.0 The
:paramref:`_sa.create_engine.isolation_level`
parameter has been generalized to work on all dialects which support
the concept of isolation level, and is provided as a more succinct,
up front configuration switch in contrast to the execution option
which is more of an ad-hoc programmatic option.
.. seealso::
:ref:`dbapi_autocommit`
: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 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.
:paramref:`_engine.Connection.execution_options.logging_token`
: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 <https://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::
:ref:`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`. This can be a float but is
subject to the limitations of Python time functions which may not be
reliable in the tens of milliseconds.
.. note: don't use 30.0 above, it seems to break with the :param tag
: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 query_cache_size: size of the cache used to cache the SQL string
form of queries. Set to zero to disable caching.
The cache is pruned of its least recently used items when its size reaches
N * 1.5. Defaults to 500, meaning the cache will always store at least
500 SQL statements when filled, and will grow up to 750 items at which
point it is pruned back down to 500 by removing the 250 least recently
used items.
Caching is accomplished on a per-statement basis by generating a
cache key that represents the statement's structure, then generating
string SQL for the current dialect only if that key is not present
in the cache. All statements support caching, however some features
such as an INSERT with a large set of parameters will intentionally
bypass the cache. SQL logging will indicate statistics for each
statement whether or not it were pull from the cache.
.. note:: some ORM functions related to unit-of-work persistence as well
as some attribute loading strategies will make use of individual
per-mapper caches outside of the main cache.
.. seealso::
:ref:`sql_caching`
.. versionadded:: 1.4
:param use_insertmanyvalues: True by default, use the "insertmanyvalues"
execution style for INSERT..RETURNING statements by default.
.. versionadded:: 2.0
.. seealso::
:ref:`engine_insertmanyvalues`
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