# `psycopg2.extensions` – Extensions to the DB API

The module contains a few objects and function extending the minimum set of functionalities defined by the DB API 2.0.

## Classes definitions

Instances of these classes are usually returned by factory functions or attributes. Their definitions are exposed here to allow subclassing, introspection etc.

class psycopg2.extensions.connection(dsn, async=False)

  Is the class usually returned by the `connect()` function. It is exposed by the `extensions` module in order to allow subclassing to extend its behaviour: the subclass should be passed to the `connect()` function using the `connection_factory` parameter. See also Connection and cursor factories.

  For a complete description of the class, see `connection`.

  Changed in version 2.7: async_ can be used as alias for async.

class psycopg2.extensions.cursor(conn, name=None)

  It is the class usually returned by the `connection.cursor()` method. It is exposed by the `extensions` module in order to allow subclassing to extend its behaviour: the subclass should be passed to the `cursor()` method using the `cursor_factory` parameter. See also Connection and cursor factories.

  For a complete description of the class, see `cursor`.

class psycopg2.extensions.lobject(conn[, oid[, mode[, new_oid[, new_file]]]])

  Wrapper for a PostgreSQL large object. See Access to PostgreSQL large objects for an overview.

  The class can be subclassed: see the `connection.lobject()` to know how to specify a `lobject` subclass.

  Added in version 2.0.8.

  oid

    Database OID of the object.

  mode

    The mode the database was open. See `connection.lobject()` for a description of the available modes.

  read(bytes=-1)

    Read a chunk of data from the current file position. If -1 (default) read all the remaining data.

    The result is an Unicode string (decoded according to `connection.encoding`) if the file was open in `t` mode, a bytes string for `b` mode.

    Changed in version 2.4: added Unicode support.

  write(str)

    Write a string to the large object. Return the number of bytes written. Unicode strings are encoded in the `connection.encoding` before writing.

    Changed in version 2.4: added Unicode support.

  export(file_name)

    Export the large object content to the file system.

    The method uses the efficient `lo_export()` libpq function.

  seek(offset, whence=0)

    Set the lobject current position.

    Changed in version 2.6: added support for offset > 2GB.

  tell()

    Return the lobject current position.

    Added in version 2.2.

    Changed in version 2.6: added support for return value > 2GB.

  truncate(len=0)

    Truncate the lobject to the given size.

    The method will only be available if Psycopg has been built against libpq from PostgreSQL 8.3 or later and can only be used with PostgreSQL servers running these versions. It uses the `lo_truncate()` libpq function.

    Added in version 2.2.

    Changed in version 2.6: added support for len > 2GB.

  Warning

  If Psycopg is built with `lo_truncate()` support or with the 64 bits API support (resp. from PostgreSQL versions 8.3 and 9.3) but at runtime an older version of the dynamic library is found, the `psycopg2` module will fail to import. See the lo_truncate FAQ about the problem.

  close()

    Close the object.

  closed

    Boolean attribute specifying if the object is closed.

  unlink()

    Close the object and remove it from the database.

class psycopg2.extensions.ConnectionInfo(connection)

  Details about the native PostgreSQL database connection.

  This class exposes several informative functions about the status of the libpq connection.

  Objects of this class are exposed as the `connection.info` attribute.

  Added in version 2.8.

  dbname

    The database name of the connection.

    See also

    libpq docs for PQdb() for details.

  user

    The user name of the connection.

    See also

    libpq docs for PQuser() for details.

  password

    The password of the connection.

    See also

    libpq docs for PQpass() for details.

  host

    The server host name of the connection.

    This can be a host name, an IP address, or a directory path if the connection is via Unix socket. (The path case can be distinguished because it will always be an absolute path, beginning with `/`.)

    See also

    libpq docs for PQhost() for details.

  port

    The port of the connection.

    Type:

      `int`

    See also

    libpq docs for PQport() for details.

  options

    The command-line options passed in the connection request.

    See also

    libpq docs for PQoptions() for details.

  dsn_parameters

    The effective connection parameters.

    Type:

      `dict`

    The results include values which weren’t explicitly set by the connection string, such as defaults, environment variables, etc. The password parameter is removed from the results.

    See also

    libpq docs for PQconninfo() for details.

    Example:

        >>> conn.info.dsn_parameters
        {'dbname': 'test', 'user': 'postgres', 'port': '5432', 'sslmode': 'prefer'}

    Requires libpq >= 9.3.

  status

    The status of the connection.

    Type:

      `int`

    See also

    libpq docs for PQstatus() for details.

  transaction_status

    The current in-transaction status of the connection.

    Symbolic constants for the values are defined in the module `psycopg2.extensions`: see Transaction status constants for the available values.

    Type:

      `int`

    See also

    libpq docs for PQtransactionStatus() for details.

  parameter_status(name)

    Looks up a current parameter setting of the server.

    Parameters:

      name (`str`) – The name of the parameter to return.

    Returns:

      The parameter value, `None` if the parameter is unknown.

    Return type:

      `str`

    See also

    libpq docs for PQparameterStatus() for details.

  protocol_version

    The frontend/backend protocol being used.

    Type:

      `int`

    See also

    libpq docs for PQprotocolVersion() for details.

    Currently Psycopg supports only protocol 3, which allows connection to PostgreSQL server from version 7.4. Psycopg versions previous than 2.3 support both protocols 2 and 3.

  server_version

    Returns an integer representing the server version.

    Type:

      `int`

    See also

    libpq docs for PQserverVersion() for details.

    The number is formed by converting the major, minor, and revision numbers into two-decimal-digit numbers and appending them together. After PostgreSQL 10 the minor version was dropped, so the second group of digits is always `00`. For example, version 9.3.5 will be returned as `90305`, version 10.2 as `100002`.

  error_message

    The error message most recently generated by an operation on the connection.

    `None` if there is no current message.

    See also

    libpq docs for PQerrorMessage() for details.

  socket

    The file descriptor number of the connection socket to the server.

    Type:

      `int`

    See also

    libpq docs for PQsocket() for details.

  backend_pid

    The process ID (PID) of the backend process you connected to.

    Type:

      `int`

    See also

    libpq docs for PQbackendPID() for details.

  needs_password

    The connection authentication method required a password, but none was available.

    Type:

      `bool`

    See also

    libpq docs for PQconnectionNeedsPassword() for details.

  used_password

    The connection authentication method used a password.

    Type:

      `bool`

    See also

    libpq docs for PQconnectionUsedPassword() for details.

  ssl_in_use

    `True` if the connection uses SSL, `False` if not.

    Only available if psycopg was built with libpq >= 9.5; raise `NotSupportedError` otherwise.

    Type:

      `bool`

    See also

    libpq docs for PQsslInUse() for details.

  ssl_attribute(name)

    Returns SSL-related information about the connection.

    Parameters:

      name (`str`) – The name of the attribute to return.

    Returns:

      The attribute value, `None` if unknown.

    Return type:

      `str`

    Only available if psycopg was built with libpq >= 9.5; raise `NotSupportedError` otherwise.

    Valid names are available in `ssl_attribute_names`.

    See also

    libpq docs for PQsslAttribute() for details.

  ssl_attribute_names

    The list of the SSL attribute names available.

    Type:

      `list` of `str`

    Only available if psycopg was built with libpq >= 9.5; raise `NotSupportedError` otherwise.

    See also

    libpq docs for PQsslAttributeNames() for details.

class psycopg2.extensions.Column(\*args, \*\*kwargs)

  Description of one result column, exposed as items of the `cursor.description` sequence.

  Added in version 2.8: in previous version the `description` attribute was a sequence of simple tuples or namedtuples.

  name

    The name of the column returned.

  type_code

    The PostgreSQL OID of the column. You can use the `pg_type` system table to get more informations about the type. This is the value used by Psycopg to decide what Python type use to represent the value. See also Type casting of SQL types into Python objects.

  display_size

    Supposed to be the actual length of the column in bytes. Obtaining this value is computationally intensive, so it is always `None`.

    Changed in version 2.8: It was previously possible to obtain this value using a compiler flag at builtin.

  internal_size

    The size in bytes of the column associated to this column on the server. Set to a negative value for variable-size types See also PQfsize.

  precision

    Total number of significant digits in columns of type `NUMERIC`. `None` for other types.

  scale

    Count of decimal digits in the fractional part in columns of type `NUMERIC`. `None` for other types.

  null_ok

    Always `None` as not easy to retrieve from the libpq.

  table_oid

    The oid of the table from which the column was fetched (matching `pg_class.oid`). `None` if the column is not a simple reference to a table column. See also PQftable.

    Added in version 2.8.

  table_column

    The number of the column (within its table) making up the result (matching `pg_attribute.attnum`, so it will start from 1). `None` if the column is not a simple reference to a table column. See also PQftablecol.

    Added in version 2.8.

class psycopg2.extensions.Notify(pid, channel, payload='')

  A notification received from the backend.

  `Notify` instances are made available upon reception on the `notifies` member of the listening connection. The object can be also accessed as a 2 items tuple returning the members `(pid,channel)` for backward compatibility.

  See Asynchronous notifications for details.

  Added in version 2.3.

  channel

    The name of the channel to which the notification was sent.

  payload

    The payload message of the notification.

    Attaching a payload to a notification is only available since PostgreSQL 9.0: for notifications received from previous versions of the server this member is always the empty string.

  pid

    The ID of the backend process that sent the notification.

    Note: if the sending session was handled by Psycopg, you can use `backend_pid` to know its PID.

class psycopg2.extensions.Xid(format_id, gtrid, bqual)

  A transaction identifier used for two-phase commit.

  Usually returned by the connection methods `xid()` and `tpc_recover()`. `Xid` instances can be unpacked as a 3-item tuples containing the items `(format_id,gtrid,bqual)`. The `str()` of the object returns the transaction ID used in the commands sent to the server.

  See Two-Phase Commit protocol support for an introduction.

  Added in version 2.3.

  static from_string(s)

    Create a `Xid` object from a string representation. Static method.

    If s is a PostgreSQL transaction ID produced by a XA transaction, the returned object will have `format_id`, `gtrid`, `bqual` set to the values of the preparing XA id. Otherwise only the `gtrid` is populated with the unparsed string. The operation is the inverse of the one performed by `str(xid)`.

  bqual

    Branch qualifier of the transaction.

    In a XA transaction every resource participating to a transaction receives a distinct branch qualifier. `None` if the transaction doesn’t follow the XA standard.

  database

    Database the recovered transaction belongs to.

  format_id

    Format ID in a XA transaction.

    A non-negative 32 bit integer. `None` if the transaction doesn’t follow the XA standard.

  gtrid

    Global transaction ID in a XA transaction.

    If the transaction doesn’t follow the XA standard, it is the plain transaction ID used in the server commands.

  owner

    Name of the user who prepared a recovered transaction.

  prepared

    Timestamp (with timezone) in which a recovered transaction was prepared.

class psycopg2.extensions.Diagnostics(exception)

  Details from a database error report.

  The object is returned by the `diag` attribute of the `Error` object. All the information available from the `PQresultErrorField()` function are exposed as attributes by the object, e.g. the `severity` attribute returns the `PG_DIAG_SEVERITY` code. Please refer to the PostgreSQL documentation for the meaning of all the attributes.

  Added in version 2.5.

  The attributes currently available are:

  column_name
  constraint_name
  context
  datatype_name
  internal_position
  internal_query
  message_detail
  message_hint
  message_primary
  schema_name
  severity
  severity_nonlocalized
  source_file
  source_function
  source_line
  sqlstate
  statement_position
  table_name

    A string with the error field if available; `None` if not available. The attribute value is available only if the error sent by the server: not all the fields are available for all the errors and for all the server versions.

    Added in version 2.8: The `severity_nonlocalized` attribute.

## SQL adaptation protocol objects

Psycopg provides a flexible system to adapt Python objects to the SQL syntax (inspired to the PEP 246), allowing serialization in PostgreSQL. See Adapting new Python types to SQL syntax for a detailed description. The following objects deal with Python objects adaptation:

psycopg2.extensions.adapt(obj)

  Return the SQL representation of obj as an `ISQLQuote`. Raise a `ProgrammingError` if how to adapt the object is unknown. In order to allow new objects to be adapted, register a new adapter for it using the `register_adapter()` function.

  The function is the entry point of the adaptation mechanism: it can be used to write adapters for complex objects by recursively calling `adapt()` on its components.

psycopg2.extensions.register_adapter(class, adapter)

  Register a new adapter for the objects of class class.

  adapter should be a function taking a single argument (the object to adapt) and returning an object conforming to the `ISQLQuote` protocol (e.g. exposing a `getquoted()` method). The `AsIs` is often useful for this task.

  Once an object is registered, it can be safely used in SQL queries and by the `adapt()` function.

class psycopg2.extensions.ISQLQuote(wrapped_object)

  Represents the SQL adaptation protocol. Objects conforming this protocol should implement a `getquoted()` and optionally a `prepare()` method.

  Adapters may subclass `ISQLQuote`, but is not necessary: it is enough to expose a `getquoted()` method to be conforming.

  _wrapped

    The wrapped object passes to the constructor

  getquoted()

    Subclasses or other conforming objects should return a valid SQL string representing the wrapped object. In Python 3 the SQL must be returned in a `bytes` object. The `ISQLQuote` implementation does nothing.

  prepare(conn)

    Prepare the adapter for a connection. The method is optional: if implemented, it will be invoked before `getquoted()` with the connection to adapt for as argument.

    A conform object can implement this method if the SQL representation depends on any server parameter, such as the server version or the `standard_conforming_string` setting. Container objects may store the connection and use it to recursively prepare contained objects: see the implementation for `psycopg2.extensions.SQL_IN` for a simple example.

class psycopg2.extensions.AsIs(object)

  Adapter conform to the `ISQLQuote` protocol useful for objects whose string representation is already valid as SQL representation.

  getquoted()

    Return the `str()` conversion of the wrapped object.

        >>> AsIs(42).getquoted()
        '42'

class psycopg2.extensions.QuotedString(str)

  Adapter conform to the `ISQLQuote` protocol for string-like objects.

  getquoted()

    Return the string enclosed in single quotes. Any single quote appearing in the string is escaped by doubling it according to SQL string constants syntax. Backslashes are escaped too.

        >>> QuotedString(r"O'Reilly").getquoted()
        "'O''Reilly'"

class psycopg2.extensions.Binary(str)

  Adapter conform to the `ISQLQuote` protocol for binary objects.

  getquoted()

    Return the string enclosed in single quotes. It performs the same escaping of the `QuotedString` adapter, plus it knows how to escape non-printable chars.

        >>> Binary("\x00\x08\x0F").getquoted()
        "'\\\\000\\\\010\\\\017'"

  Changed in version 2.0.14: previously the adapter was not exposed by the `extensions` module. In older versions it can be imported from the implementation module `psycopg2._psycopg`.

class psycopg2.extensions.Boolean
class psycopg2.extensions.Float
class psycopg2.extensions.SQL_IN

  Specialized adapters for builtin objects.

class psycopg2.extensions.DateFromPy
class psycopg2.extensions.TimeFromPy
class psycopg2.extensions.TimestampFromPy
class psycopg2.extensions.IntervalFromPy

  Specialized adapters for Python datetime objects.

psycopg2.extensions.adapters

  Dictionary of the currently registered object adapters. Use `register_adapter()` to add an adapter for a new type.

## Database types casting functions

These functions are used to manipulate type casters to convert from PostgreSQL types to Python objects. See Type casting of SQL types into Python objects for details.

psycopg2.extensions.new_type(oids, name, adapter)

  Create a new type caster to convert from a PostgreSQL type to a Python object. The object created must be registered using `register_type()` to be used.

  Parameters:

    - oids – tuple of OIDs of the PostgreSQL type to convert.

    - name – the name of the new type adapter.

    - adapter – the adaptation function.

  The object OID can be read from the `cursor.description` attribute or by querying from the PostgreSQL catalog.

  adapter should have signature `fun(value, cur)` where value is the string representation returned by PostgreSQL and cur is the cursor from which data are read. In case of `NULL`, value will be `None`. The adapter should return the converted object.

  See Type casting of SQL types into Python objects for an usage example.

psycopg2.extensions.new_array_type(oids, name, base_caster)

  Create a new type caster to convert from a PostgreSQL array type to a list of Python object. The object created must be registered using `register_type()` to be used.

  Parameters:

    - oids – tuple of OIDs of the PostgreSQL type to convert. It should probably contain the oid of the array type (e.g. the `typarray` field in the `pg_type` table).

    - name – the name of the new type adapter.

    - base_caster – a Psycopg typecaster, e.g. created using the `new_type()` function. The caster should be able to parse a single item of the desired type.

  Added in version 2.4.3.

  Note

  The function can be used to create a generic array typecaster, returning a list of strings: just use `psycopg2.STRING` as base typecaster. For instance, if you want to receive an array of `macaddr` from the database, each address represented by string, you can use:

      # select typarray from pg_type where typname = 'macaddr' -> 1040
      psycopg2.extensions.register_type(
          psycopg2.extensions.new_array_type(
              (1040,), 'MACADDR[]', psycopg2.STRING))

psycopg2.extensions.register_type(obj[, scope])

  Register a type caster created using `new_type()`.

  If scope is specified, it should be a `connection` or a `cursor`: the type caster will be effective only limited to the specified object. Otherwise it will be globally registered.

psycopg2.extensions.string_types

  The global register of type casters.

psycopg2.extensions.encodings

  Mapping from PostgreSQL encoding to Python encoding names. Used by Psycopg when adapting or casting unicode strings. See Unicode handling.

## Additional exceptions

The module exports a few exceptions in addition to the standard ones defined by the DB API 2.0.

Note

From psycopg 2.8 these error classes are also exposed by the `psycopg2.errors` module.

exception psycopg2.extensions.QueryCanceledError

  (subclasses `OperationalError`)

  Error related to SQL query cancellation. It can be trapped specifically to detect a timeout.

  Added in version 2.0.7.

exception psycopg2.extensions.TransactionRollbackError

  (subclasses `OperationalError`)

  Error causing transaction rollback (deadlocks, serialization failures, etc). It can be trapped specifically to detect a deadlock.

  Added in version 2.0.7.

## Coroutines support functions

These functions are used to set and retrieve the callback function for cooperation with coroutine libraries.

Added in version 2.2.

psycopg2.extensions.set_wait_callback(f)

  Register a callback function to block waiting for data.

  The callback should have signature `fun(conn)` and is called to wait for data available whenever a blocking function from the libpq is called. Use `set_wait_callback(None)` to revert to the original behaviour (i.e. using blocking libpq functions).

  The function is an hook to allow coroutine-based libraries (such as Eventlet or gevent) to switch when Psycopg is blocked, allowing other coroutines to run concurrently.

  See `wait_select()` for an example of a wait callback implementation.

psycopg2.extensions.get_wait_callback()

  Return the currently registered wait callback.

  Return `None` if no callback is currently registered.

## Other functions

psycopg2.extensions.libpq_version()

  Return the version number of the `libpq` dynamic library loaded as an integer, in the same format of `server_version`.

  Raise `NotSupportedError` if the `psycopg2` module was compiled with a `libpq` version lesser than 9.1 (which can be detected by the `__libpq_version__` constant).

  Added in version 2.7.

  See also

  libpq docs for PQlibVersion().

psycopg2.extensions.make_dsn(dsn=None, \*\*kwargs)

  Create a valid connection string from arguments.

  Put together the arguments in kwargs into a connection string. If dsn is specified too, merge the arguments coming from both the sources. If the same argument name is specified in both the sources, the kwargs value overrides the dsn value.

  The input arguments are validated: the output should always be a valid connection string (as far as `parse_dsn()` is concerned). If not raise `ProgrammingError`.

  Example:

      >>> from psycopg2.extensions import make_dsn
      >>> make_dsn('dbname=foo host=example.com', password="s3cr3t")
      'host=example.com password=s3cr3t dbname=foo'

  Added in version 2.7.

psycopg2.extensions.parse_dsn(dsn)

  Parse connection string into a dictionary of keywords and values.

  Parsing is delegated to the libpq: different versions of the client library may support different formats or parameters (for example, connection URIs are only supported from libpq 9.2). Raise `ProgrammingError` if the dsn is not valid.

  Example:

      >>> from psycopg2.extensions import parse_dsn
      >>> parse_dsn('dbname=test user=postgres password=secret')
      {'password': 'secret', 'user': 'postgres', 'dbname': 'test'}
      >>> parse_dsn("postgresql://someone@example.com/somedb?connect_timeout=10")
      {'host': 'example.com', 'user': 'someone', 'dbname': 'somedb', 'connect_timeout': '10'}

  Added in version 2.7.

  See also

  libpq docs for PQconninfoParse().

psycopg2.extensions.quote_ident(str, scope)

  Return quoted identifier according to PostgreSQL quoting rules.

  The scope must be a `connection` or a `cursor`, the underlying connection encoding is used for any necessary character conversion.

  Added in version 2.7.

  See also

  libpq docs for PQescapeIdentifier()

psycopg2.extensions.encrypt_password(password, user, scope=None, algorithm=None)

  Return the encrypted form of a PostgreSQL password.

  Parameters:

    - password – the cleartext password to encrypt

    - user – the name of the user to use the password for

    - scope (`connection` or `cursor`) – the scope to encrypt the password into; if algorithm is `md5` it can be `None`

    - algorithm – the password encryption algorithm to use

  The algorithm `md5` is always supported. Other algorithms are only supported if the client libpq version is at least 10 and may require a compatible server version: check the PostgreSQL encryption documentation to know the algorithms supported by your server.

  Using `None` as algorithm will result in querying the server to know the current server password encryption setting, which is a blocking operation: query the server separately and specify a value for algorithm if you want to maintain a non-blocking behaviour.

  Added in version 2.8.

  See also

  PostgreSQL docs for the password_encryption setting, libpq PQencryptPasswordConn(), PQencryptPassword() functions.

## Isolation level constants

Psycopg2 `connection` objects hold informations about the PostgreSQL transaction isolation level. By default Psycopg doesn’t change the default configuration of the server (`ISOLATION_LEVEL_DEFAULT`); the default for PostgreSQL servers is typically `READ COMMITTED`, but this may be changed in the server configuration files. A different isolation level can be set through the `set_isolation_level()` or `set_session()` methods. The level can be set to one of the following constants:

psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT

  No transaction is started when commands are executed and no `commit()` or `rollback()` is required. Some PostgreSQL command such as `CREATE DATABASE` or `VACUUM` can’t run into a transaction: to run such command use:

      >>> conn.set_isolation_level(ISOLATION_LEVEL_AUTOCOMMIT)

  See also Transactions control.

psycopg2.extensions.ISOLATION_LEVEL_READ_UNCOMMITTED

  The `READ UNCOMMITTED` isolation level is defined in the SQL standard but not available in the MVCC model of PostgreSQL: it is replaced by the stricter `READ COMMITTED`.

psycopg2.extensions.ISOLATION_LEVEL_READ_COMMITTED

  This is usually the default PostgreSQL value, but a different default may be set in the database configuration.

  A new transaction is started at the first `execute()` command on a cursor and at each new `execute()` after a `commit()` or a `rollback()`. The transaction runs in the PostgreSQL `READ COMMITTED` isolation level: a `SELECT` query sees only data committed before the query began; it never sees either uncommitted data or changes committed during query execution by concurrent transactions.

  See also

  Read Committed Isolation Level in PostgreSQL documentation.

psycopg2.extensions.ISOLATION_LEVEL_REPEATABLE_READ

  As in `ISOLATION_LEVEL_READ_COMMITTED`, a new transaction is started at the first `execute()` command. Transactions run at a `REPEATABLE READ` isolation level: all the queries in a transaction see a snapshot as of the start of the transaction, not as of the start of the current query within the transaction. However applications using this level must be prepared to retry transactions due to serialization failures.

  While this level provides a guarantee that each transaction sees a completely stable view of the database, this view will not necessarily always be consistent with some serial (one at a time) execution of concurrent transactions of the same level.

  Changed in version 2.4.2: The value was an alias for `ISOLATION_LEVEL_SERIALIZABLE` before. The two levels are distinct since PostgreSQL 9.1

  See also

  Repeatable Read Isolation Level in PostgreSQL documentation.

psycopg2.extensions.ISOLATION_LEVEL_SERIALIZABLE

  As in `ISOLATION_LEVEL_READ_COMMITTED`, a new transaction is started at the first `execute()` command. Transactions run at a `SERIALIZABLE` isolation level. This is the strictest transactions isolation level, equivalent to having the transactions executed serially rather than concurrently. However applications using this level must be prepared to retry transactions due to serialization failures.

  Starting from PostgreSQL 9.1, this mode monitors for conditions which could make execution of a concurrent set of serializable transactions behave in a manner inconsistent with all possible serial (one at a time) executions of those transaction. In previous version the behaviour was the same of the `REPEATABLE READ` isolation level.

  See also

  Serializable Isolation Level in PostgreSQL documentation.

psycopg2.extensions.ISOLATION_LEVEL_DEFAULT

  A new transaction is started at the first `execute()` command, but the isolation level is not explicitly selected by Psycopg: the server will use whatever level is defined in its configuration or by statements executed within the session outside Pyscopg control. If you want to know what the value is you can use a query such as `show transaction_isolation`.

  Added in version 2.7.

## Transaction status constants

These values represent the possible status of a transaction: the current value can be read using the `connection.info.transaction_status` property.

psycopg2.extensions.TRANSACTION_STATUS_IDLE

  The session is idle and there is no current transaction.

psycopg2.extensions.TRANSACTION_STATUS_ACTIVE

  A command is currently in progress.

psycopg2.extensions.TRANSACTION_STATUS_INTRANS

  The session is idle in a valid transaction block.

psycopg2.extensions.TRANSACTION_STATUS_INERROR

  The session is idle in a failed transaction block.

psycopg2.extensions.TRANSACTION_STATUS_UNKNOWN

  Reported if the connection with the server is bad.

## Connection status constants

These values represent the possible status of a connection: the current value can be read from the `status` attribute.

It is possible to find the connection in other status than the one shown below. Those are the only states in which a working connection is expected to be found during the execution of regular Python client code: other states are for internal usage and Python code should not rely on them.

psycopg2.extensions.STATUS_READY

  Connection established. No transaction in progress.

psycopg2.extensions.STATUS_BEGIN

  Connection established. A transaction is currently in progress.

psycopg2.extensions.STATUS_IN_TRANSACTION

  An alias for `STATUS_BEGIN`

psycopg2.extensions.STATUS_PREPARED

  The connection has been prepared for the second phase in a two-phase commit transaction. The connection can’t be used to send commands to the database until the transaction is finished with `tpc_commit()` or `tpc_rollback()`.

  Added in version 2.3.

## Poll constants

Added in version 2.2.

These values can be returned by `connection.poll()` during asynchronous connection and communication. They match the values in the libpq enum `PostgresPollingStatusType`. See Asynchronous support and Support for coroutine libraries.

psycopg2.extensions.POLL_OK

  The data being read is available, or the file descriptor is ready for writing: reading or writing will not block.

psycopg2.extensions.POLL_READ

  Some data is being read from the backend, but it is not available yet on the client and reading would block. Upon receiving this value, the client should wait for the connection file descriptor to be ready for reading. For example:

      select.select([conn.fileno()], [], [])

psycopg2.extensions.POLL_WRITE

  Some data is being sent to the backend but the connection file descriptor can’t currently accept new data. Upon receiving this value, the client should wait for the connection file descriptor to be ready for writing. For example:

      select.select([], [conn.fileno()], [])

psycopg2.extensions.POLL_ERROR

  There was a problem during connection polling. This value should actually never be returned: in case of poll error usually an exception containing the relevant details is raised.

## Additional database types

The `extensions` module includes typecasters for many standard PostgreSQL types. These objects allow the conversion of returned data into Python objects. All the typecasters are automatically registered, except `UNICODE` and `UNICODEARRAY`: you can register them using `register_type()` in order to receive Unicode objects instead of strings from the database. See Unicode handling for details.

psycopg2.extensions.BOOLEAN
psycopg2.extensions.BYTES
psycopg2.extensions.DATE
psycopg2.extensions.DECIMAL
psycopg2.extensions.FLOAT
psycopg2.extensions.INTEGER
psycopg2.extensions.INTERVAL
psycopg2.extensions.LONGINTEGER
psycopg2.extensions.TIME
psycopg2.extensions.UNICODE

  Typecasters for basic types. Note that a few other ones (`BINARY`, `DATETIME`, `NUMBER`, `ROWID`, `STRING`) are exposed by the `psycopg2` module for DB API 2.0 compliance.

psycopg2.extensions.BINARYARRAY
psycopg2.extensions.BOOLEANARRAY
psycopg2.extensions.BYTESARRAY
psycopg2.extensions.DATEARRAY
psycopg2.extensions.DATETIMEARRAY
psycopg2.extensions.DECIMALARRAY
psycopg2.extensions.FLOATARRAY
psycopg2.extensions.INTEGERARRAY
psycopg2.extensions.INTERVALARRAY
psycopg2.extensions.LONGINTEGERARRAY
psycopg2.extensions.ROWIDARRAY
psycopg2.extensions.STRINGARRAY
psycopg2.extensions.TIMEARRAY
psycopg2.extensions.UNICODEARRAY

  Typecasters to convert arrays of sql types into Python lists.

psycopg2.extensions.PYDATE
psycopg2.extensions.PYDATETIME
psycopg2.extensions.PYDATETIMETZ
psycopg2.extensions.PYINTERVAL
psycopg2.extensions.PYTIME
psycopg2.extensions.PYDATEARRAY
psycopg2.extensions.PYDATETIMEARRAY
psycopg2.extensions.PYDATETIMETZARRAY
psycopg2.extensions.PYINTERVALARRAY
psycopg2.extensions.PYTIMEARRAY

  Typecasters to convert time-related data types to Python `datetime` objects.

Changed in version 2.2: previously the `DECIMAL` typecaster and the specific time-related typecasters (`PY*` and `MX*`) were not exposed by the `extensions` module. In older versions they can be imported from the implementation module `psycopg2._psycopg`.

Added in version 2.7.2: the `*DATETIMETZ*` objects.

Added in version 2.8: the `BYTES` and `BYTESARRAY` objects.