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<div class="section" id="the-connection-class">
<h1>The <code class="docutils literal"><span class="pre">connection</span></code> class<a class="headerlink" href="#the-connection-class" title="Permalink to this headline">¶</a></h1>
<dl class="class">
<dt id="connection">
<em class="property">class </em><code class="descname">connection</code><a class="headerlink" href="#connection" title="Permalink to this definition">¶</a></dt>
<dd><p>Handles the connection to a PostgreSQL database instance. It encapsulates
a database session.</p>
<p>Connections are created using the factory function
<a class="reference internal" href="module.html#psycopg2.connect" title="psycopg2.connect"><code class="xref py py-obj docutils literal"><span class="pre">connect()</span></code></a>.</p>
<p>Connections are thread safe and can be shared among many threads. See
<a class="reference internal" href="usage.html#thread-safety"><span>Thread and process safety</span></a> for details.</p>
<dl class="method">
<dt id="connection.cursor">
<code class="descname">cursor</code><span class="sig-paren">(</span><em>name=None</em>, <em>cursor_factory=None</em>, <em>scrollable=None</em>, <em>withhold=False</em><span class="sig-paren">)</span><a class="headerlink" href="#connection.cursor" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a new <a class="reference internal" href="cursor.html#cursor" title="cursor"><code class="xref py py-obj docutils literal"><span class="pre">cursor</span></code></a> object using the connection.</p>
<p>If <em>name</em> is specified, the returned cursor will be a <a class="reference internal" href="usage.html#server-side-cursors"><span>server
side cursor</span></a> (also known as <em>named cursor</em>).
Otherwise it will be a regular <em>client side</em> cursor. By default a
named cursor is declared without <code class="sql docutils literal"><span class="pre">SCROLL</span></code> option and
<code class="sql docutils literal"><span class="pre">WITHOUT</span> <span class="pre">HOLD</span></code>: set the argument or property <a class="reference internal" href="cursor.html#cursor.scrollable" title="cursor.scrollable"><code class="xref py py-obj docutils literal"><span class="pre">scrollable</span></code></a>
to <code class="xref py py-obj docutils literal"><span class="pre">True</span></code>/<code class="xref py py-obj docutils literal"><span class="pre">False</span></code> and or <a class="reference internal" href="cursor.html#cursor.withhold" title="cursor.withhold"><code class="xref py py-obj docutils literal"><span class="pre">withhold</span></code></a> to <code class="xref py py-obj docutils literal"><span class="pre">True</span></code> to change the
declaration.</p>
<p>The name can be a string not valid as a PostgreSQL identifier: for
example it may start with a digit and contain non-alphanumeric
characters and quotes.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.4: </span>previously only valid PostgreSQL identifiers were accepted as
cursor name.</p>
</div>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">It is unsafe to expose the <em>name</em> to an untrusted source, for
instance you shouldn’t allow <em>name</em> to be read from a HTML form.
Consider it as part of the query, not as a query parameter.</p>
</div>
<p>The <em>cursor_factory</em> argument can be used to create non-standard
cursors. The class returned must be a subclass of
<a class="reference internal" href="extensions.html#psycopg2.extensions.cursor" title="psycopg2.extensions.cursor"><code class="xref py py-obj docutils literal"><span class="pre">psycopg2.extensions.cursor</span></code></a>. See <a class="reference internal" href="advanced.html#subclassing-cursor"><span>Connection and cursor factories</span></a> for
details. A default factory for the connection can also be specified
using the <a class="reference internal" href="#connection.cursor_factory" title="connection.cursor_factory"><code class="xref py py-obj docutils literal"><span class="pre">cursor_factory</span></code></a> attribute.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.4.3: </span>added the <em>withhold</em> argument.</p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.5: </span>added the <em>scrollable</em> argument.</p>
</div>
<div class="admonition-db-api-extension dbapi-extension admonition">
<p class="first admonition-title">DB API extension</p>
<p class="last">All the function arguments are Psycopg extensions to the DB API 2.0.</p>
</div>
</dd></dl>
<span class="target" id="index-0"></span><dl class="method">
<dt id="connection.commit">
<code class="descname">commit</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.commit" title="Permalink to this definition">¶</a></dt>
<dd><p>Commit any pending transaction to the database.</p>
<p>By default, Psycopg opens a transaction before executing the first
command: if <code class="xref py py-obj docutils literal"><span class="pre">commit()</span></code> is not called, the effect of any data
manipulation will be lost.</p>
<p>The connection can be also set in “autocommit” mode: no transaction is
automatically open, commands have immediate effect. See
<a class="reference internal" href="usage.html#transactions-control"><span>Transactions control</span></a> for details.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.5: </span>if the connection is used in a <code class="docutils literal"><span class="pre">with</span></code>
statement, the method is automatically called if no exception is
raised in the <code class="docutils literal"><span class="pre">with</span></code> block.</p>
</div>
</dd></dl>
<span class="target" id="index-1"></span><dl class="method">
<dt id="connection.rollback">
<code class="descname">rollback</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.rollback" title="Permalink to this definition">¶</a></dt>
<dd><p>Roll back to the start of any pending transaction. Closing a
connection without committing the changes first will cause an implicit
rollback to be performed.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.5: </span>if the connection is used in a <code class="docutils literal"><span class="pre">with</span></code>
statement, the method is automatically called if an exception is
raised in the <code class="docutils literal"><span class="pre">with</span></code> block.</p>
</div>
</dd></dl>
<dl class="method">
<dt id="connection.close">
<code class="descname">close</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.close" title="Permalink to this definition">¶</a></dt>
<dd><p>Close the connection now (rather than whenever <code class="xref py py-obj docutils literal"><span class="pre">del</span></code> is executed).
The connection will be unusable from this point forward; an
<a class="reference internal" href="module.html#psycopg2.InterfaceError" title="psycopg2.InterfaceError"><code class="xref py py-obj docutils literal"><span class="pre">InterfaceError</span></code></a> will be raised if any operation is
attempted with the connection. The same applies to all cursor objects
trying to use the connection. Note that closing a connection without
committing the changes first will cause any pending change to be
discarded as if a <code class="sql docutils literal"><span class="pre">ROLLBACK</span></code> was performed (unless a different
isolation level has been selected: see
<a class="reference internal" href="#connection.set_isolation_level" title="connection.set_isolation_level"><code class="xref py py-obj docutils literal"><span class="pre">set_isolation_level()</span></code></a>).</p>
<div class="versionchanged" id="index-2">
<p><span class="versionmodified">Changed in version 2.2: </span>previously an explicit <code class="sql docutils literal"><span class="pre">ROLLBACK</span></code> was issued by Psycopg on
<code class="xref py py-obj docutils literal"><span class="pre">close()</span></code>. The command could have been sent to the backend at an
inappropriate time, so Psycopg currently relies on the backend to
implicitly discard uncommitted changes. Some middleware are known
to behave incorrectly though when the connection is closed during
a transaction (when <a class="reference internal" href="#connection.status" title="connection.status"><code class="xref py py-obj docutils literal"><span class="pre">status</span></code></a> is
<a class="reference internal" href="extensions.html#psycopg2.extensions.STATUS_IN_TRANSACTION" title="psycopg2.extensions.STATUS_IN_TRANSACTION"><code class="xref py py-obj docutils literal"><span class="pre">STATUS_IN_TRANSACTION</span></code></a>), e.g. <a class="reference external" href="http://pgbouncer.projects.postgresql.org/">PgBouncer</a>
reports an <code class="docutils literal"><span class="pre">unclean</span> <span class="pre">server</span></code> and discards the connection. To
avoid this problem you can ensure to terminate the transaction
with a <a class="reference internal" href="#connection.commit" title="connection.commit"><code class="xref py py-obj docutils literal"><span class="pre">commit()</span></code></a>/<a class="reference internal" href="#connection.rollback" title="connection.rollback"><code class="xref py py-obj docutils literal"><span class="pre">rollback()</span></code></a> before
closing.</p>
</div>
</dd></dl>
<p class="rubric" id="index-3">Exceptions as connection class attributes</p>
<p>The <code class="xref py py-obj docutils literal"><span class="pre">connection</span></code> also exposes as attributes the same exceptions
available in the <a class="reference internal" href="module.html#module-psycopg2" title="psycopg2"><code class="xref py py-obj docutils literal"><span class="pre">psycopg2</span></code></a> module. See <a class="reference internal" href="module.html#dbapi-exceptions"><span>Exceptions</span></a>.</p>
<p class="rubric" id="index-4">Two-phase commit support methods</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.3.</span></p>
</div>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last"><a class="reference internal" href="usage.html#tpc"><span>Two-Phase Commit protocol support</span></a> for an introductory explanation of these methods.</p>
</div>
<p>Note that PostgreSQL supports two-phase commit since release 8.1: these
methods raise <a class="reference internal" href="module.html#psycopg2.NotSupportedError" title="psycopg2.NotSupportedError"><code class="xref py py-obj docutils literal"><span class="pre">NotSupportedError</span></code></a> if used with an older version
server.</p>
<span class="target" id="tpc-methods"></span><dl class="method">
<dt id="connection.xid">
<code class="descname">xid</code><span class="sig-paren">(</span><em>format_id</em>, <em>gtrid</em>, <em>bqual</em><span class="sig-paren">)</span><a class="headerlink" href="#connection.xid" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns a <code class="xref py py-obj docutils literal"><span class="pre">Xid</span></code> instance to be passed to the
<code class="xref py py-obj docutils literal"><span class="pre">tpc_*()</span></code> methods of this connection. The argument types and
constraints are explained in <a class="reference internal" href="usage.html#tpc"><span>Two-Phase Commit protocol support</span></a>.</p>
<p>The values passed to the method will be available on the returned
object as the members <code class="xref py py-obj docutils literal"><span class="pre">format_id</span></code>,
<code class="xref py py-obj docutils literal"><span class="pre">gtrid</span></code>, <code class="xref py py-obj docutils literal"><span class="pre">bqual</span></code>.
The object also allows accessing to these members and unpacking as a
3-items tuple.</p>
</dd></dl>
<dl class="method">
<dt id="connection.tpc_begin">
<code class="descname">tpc_begin</code><span class="sig-paren">(</span><em>xid</em><span class="sig-paren">)</span><a class="headerlink" href="#connection.tpc_begin" title="Permalink to this definition">¶</a></dt>
<dd><p>Begins a TPC transaction with the given transaction ID <em>xid</em>.</p>
<p>This method should be called outside of a transaction (i.e. nothing
may have executed since the last <a class="reference internal" href="#connection.commit" title="connection.commit"><code class="xref py py-obj docutils literal"><span class="pre">commit()</span></code></a> or
<a class="reference internal" href="#connection.rollback" title="connection.rollback"><code class="xref py py-obj docutils literal"><span class="pre">rollback()</span></code></a> and <a class="reference internal" href="#connection.status" title="connection.status"><code class="xref py py-obj docutils literal"><span class="pre">connection.status</span></code></a> is
<a class="reference internal" href="extensions.html#psycopg2.extensions.STATUS_READY" title="psycopg2.extensions.STATUS_READY"><code class="xref py py-obj docutils literal"><span class="pre">STATUS_READY</span></code></a>).</p>
<p>Furthermore, it is an error to call <code class="xref py py-obj docutils literal"><span class="pre">commit()</span></code> or <code class="xref py py-obj docutils literal"><span class="pre">rollback()</span></code>
within the TPC transaction: in this case a <a class="reference internal" href="module.html#psycopg2.ProgrammingError" title="psycopg2.ProgrammingError"><code class="xref py py-obj docutils literal"><span class="pre">ProgrammingError</span></code></a>
is raised.</p>
<p>The <em>xid</em> may be either an object returned by the <a class="reference internal" href="#connection.xid" title="connection.xid"><code class="xref py py-obj docutils literal"><span class="pre">xid()</span></code></a>
method or a plain string: the latter allows to create a transaction
using the provided string as PostgreSQL transaction id. See also
<a class="reference internal" href="#connection.tpc_recover" title="connection.tpc_recover"><code class="xref py py-obj docutils literal"><span class="pre">tpc_recover()</span></code></a>.</p>
</dd></dl>
<span class="target" id="index-5"></span><dl class="method">
<dt id="connection.tpc_prepare">
<code class="descname">tpc_prepare</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.tpc_prepare" title="Permalink to this definition">¶</a></dt>
<dd><p>Performs the first phase of a transaction started with
<a class="reference internal" href="#connection.tpc_begin" title="connection.tpc_begin"><code class="xref py py-obj docutils literal"><span class="pre">tpc_begin()</span></code></a>. A <a class="reference internal" href="module.html#psycopg2.ProgrammingError" title="psycopg2.ProgrammingError"><code class="xref py py-obj docutils literal"><span class="pre">ProgrammingError</span></code></a> is raised if
this method is used outside of a TPC transaction.</p>
<p>After calling <code class="xref py py-obj docutils literal"><span class="pre">tpc_prepare()</span></code>, no statements can be executed until
<a class="reference internal" href="#connection.tpc_commit" title="connection.tpc_commit"><code class="xref py py-obj docutils literal"><span class="pre">tpc_commit()</span></code></a> or <a class="reference internal" href="#connection.tpc_rollback" title="connection.tpc_rollback"><code class="xref py py-obj docutils literal"><span class="pre">tpc_rollback()</span></code></a> will be
called. The <a class="reference internal" href="#connection.reset" title="connection.reset"><code class="xref py py-obj docutils literal"><span class="pre">reset()</span></code></a> method can be used to restore the
status of the connection to <a class="reference internal" href="extensions.html#psycopg2.extensions.STATUS_READY" title="psycopg2.extensions.STATUS_READY"><code class="xref py py-obj docutils literal"><span class="pre">STATUS_READY</span></code></a>: the
transaction will remain prepared in the database and will be
possible to finish it with <code class="xref py py-obj docutils literal"><span class="pre">tpc_commit(xid)</span></code> and
<code class="xref py py-obj docutils literal"><span class="pre">tpc_rollback(xid)</span></code>.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">the <a class="reference external" href="http://www.postgresql.org/docs/current/static/sql-prepare-transaction.html"><code class="sql docutils literal"><span class="pre">PREPARE</span> <span class="pre">TRANSACTION</span></code></a> PostgreSQL command.</p>
</div>
</dd></dl>
<span class="target" id="index-6"></span><dl class="method">
<dt id="connection.tpc_commit">
<code class="descname">tpc_commit</code><span class="sig-paren">(</span><span class="optional">[</span><em>xid</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.tpc_commit" title="Permalink to this definition">¶</a></dt>
<dd><p>When called with no arguments, <code class="xref py py-obj docutils literal"><span class="pre">tpc_commit()</span></code> commits a TPC
transaction previously prepared with <a class="reference internal" href="#connection.tpc_prepare" title="connection.tpc_prepare"><code class="xref py py-obj docutils literal"><span class="pre">tpc_prepare()</span></code></a>.</p>
<p>If <code class="xref py py-obj docutils literal"><span class="pre">tpc_commit()</span></code> is called prior to <code class="xref py py-obj docutils literal"><span class="pre">tpc_prepare()</span></code>, a single phase
commit is performed. A transaction manager may choose to do this if
only a single resource is participating in the global transaction.</p>
<p>When called with a transaction ID <em>xid</em>, the database commits
the given transaction. If an invalid transaction ID is
provided, a <a class="reference internal" href="module.html#psycopg2.ProgrammingError" title="psycopg2.ProgrammingError"><code class="xref py py-obj docutils literal"><span class="pre">ProgrammingError</span></code></a> will be raised. This form
should be called outside of a transaction, and is intended for use in
recovery.</p>
<p>On return, the TPC transaction is ended.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">the <a class="reference external" href="http://www.postgresql.org/docs/current/static/sql-commit-prepared.html"><code class="sql docutils literal"><span class="pre">COMMIT</span> <span class="pre">PREPARED</span></code></a> PostgreSQL command.</p>
</div>
</dd></dl>
<span class="target" id="index-7"></span><dl class="method">
<dt id="connection.tpc_rollback">
<code class="descname">tpc_rollback</code><span class="sig-paren">(</span><span class="optional">[</span><em>xid</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.tpc_rollback" title="Permalink to this definition">¶</a></dt>
<dd><p>When called with no arguments, <code class="xref py py-obj docutils literal"><span class="pre">tpc_rollback()</span></code> rolls back a TPC
transaction. It may be called before or after
<a class="reference internal" href="#connection.tpc_prepare" title="connection.tpc_prepare"><code class="xref py py-obj docutils literal"><span class="pre">tpc_prepare()</span></code></a>.</p>
<p>When called with a transaction ID <em>xid</em>, it rolls back the given
transaction. If an invalid transaction ID is provided, a
<a class="reference internal" href="module.html#psycopg2.ProgrammingError" title="psycopg2.ProgrammingError"><code class="xref py py-obj docutils literal"><span class="pre">ProgrammingError</span></code></a> is raised. This form should be called
outside of a transaction, and is intended for use in recovery.</p>
<p>On return, the TPC transaction is ended.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">the <a class="reference external" href="http://www.postgresql.org/docs/current/static/sql-rollback-prepared.html"><code class="sql docutils literal"><span class="pre">ROLLBACK</span> <span class="pre">PREPARED</span></code></a> PostgreSQL command.</p>
</div>
</dd></dl>
<span class="target" id="index-8"></span><dl class="method">
<dt id="connection.tpc_recover">
<code class="descname">tpc_recover</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.tpc_recover" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns a list of <code class="xref py py-obj docutils literal"><span class="pre">Xid</span></code> representing pending
transactions, suitable for use with <a class="reference internal" href="#connection.tpc_commit" title="connection.tpc_commit"><code class="xref py py-obj docutils literal"><span class="pre">tpc_commit()</span></code></a> or
<a class="reference internal" href="#connection.tpc_rollback" title="connection.tpc_rollback"><code class="xref py py-obj docutils literal"><span class="pre">tpc_rollback()</span></code></a>.</p>
<p>If a transaction was not initiated by Psycopg, the returned Xids will
have attributes <code class="xref py py-obj docutils literal"><span class="pre">format_id</span></code> and
<code class="xref py py-obj docutils literal"><span class="pre">bqual</span></code> set to <code class="xref py py-obj docutils literal"><span class="pre">None</span></code> and the
<code class="xref py py-obj docutils literal"><span class="pre">gtrid</span></code> set to the PostgreSQL transaction ID: such Xids are still
usable for recovery. Psycopg uses the same algorithm of the
<a class="reference external" href="http://jdbc.postgresql.org/">PostgreSQL JDBC driver</a> to encode a XA triple in a string, so
transactions initiated by a program using such driver should be
unpacked correctly.</p>
<p>Xids returned by <code class="xref py py-obj docutils literal"><span class="pre">tpc_recover()</span></code> also have extra attributes
<code class="xref py py-obj docutils literal"><span class="pre">prepared</span></code>, <code class="xref py py-obj docutils literal"><span class="pre">owner</span></code>,
<code class="xref py py-obj docutils literal"><span class="pre">database</span></code> populated with the values read
from the server.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">the <a class="reference external" href="http://www.postgresql.org/docs/current/static/view-pg-prepared-xacts.html"><code class="xref py py-obj docutils literal"><span class="pre">pg_prepared_xacts</span></code></a> system view.</p>
</div>
</dd></dl>
<div class="admonition-db-api-extension dbapi-extension admonition">
<p class="first admonition-title">DB API extension</p>
<p class="last">The above methods are the only ones defined by the DB API 2.0 protocol.
The Psycopg connection objects exports the following additional
methods and attributes.</p>
</div>
<dl class="attribute">
<dt id="connection.closed">
<code class="descname">closed</code><a class="headerlink" href="#connection.closed" title="Permalink to this definition">¶</a></dt>
<dd><p>Read-only integer attribute: 0 if the connection is open, nonzero if
it is closed or broken.</p>
</dd></dl>
<dl class="method">
<dt id="connection.cancel">
<code class="descname">cancel</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.cancel" title="Permalink to this definition">¶</a></dt>
<dd><p>Cancel the current database operation.</p>
<p>The method interrupts the processing of the current operation. If no
query is being executed, it does nothing. You can call this function
from a different thread than the one currently executing a database
operation, for instance if you want to cancel a long running query if a
button is pushed in the UI. Interrupting query execution will cause the
cancelled method to raise a
<a class="reference internal" href="extensions.html#psycopg2.extensions.QueryCanceledError" title="psycopg2.extensions.QueryCanceledError"><code class="xref py py-obj docutils literal"><span class="pre">QueryCanceledError</span></code></a>. Note that the termination
of the query is not guaranteed to succeed: see the documentation for
<a class="reference external" href="http://www.postgresql.org/docs/current/static/libpq-cancel.html#LIBPQ-PQCANCEL"><code class="xref py py-obj docutils literal"><span class="pre">PQcancel()</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.3.</span></p>
</div>
</dd></dl>
<dl class="method">
<dt id="connection.reset">
<code class="descname">reset</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.reset" title="Permalink to this definition">¶</a></dt>
<dd><p>Reset the connection to the default.</p>
<p>The method rolls back an eventual pending transaction and executes the
PostgreSQL <a class="reference external" href="http://www.postgresql.org/docs/current/static/sql-reset.html"><code class="sql docutils literal"><span class="pre">RESET</span></code></a> and <a class="reference external" href="http://www.postgresql.org/docs/current/static/sql-set-session-authorization.html"><code class="sql docutils literal"><span class="pre">SET</span> <span class="pre">SESSION</span> <span class="pre">AUTHORIZATION</span></code></a> to revert the
session to the default values. A two-phase commit transaction prepared
using <a class="reference internal" href="#connection.tpc_prepare" title="connection.tpc_prepare"><code class="xref py py-obj docutils literal"><span class="pre">tpc_prepare()</span></code></a> will remain in the database
available for recover.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.0.12.</span></p>
</div>
</dd></dl>
<dl class="attribute">
<dt id="connection.dsn">
<code class="descname">dsn</code><a class="headerlink" href="#connection.dsn" title="Permalink to this definition">¶</a></dt>
<dd><p>Read-only string containing the connection string used by the
connection.</p>
</dd></dl>
<span class="target" id="index-9"></span><dl class="method">
<dt id="connection.set_session">
<code class="descname">set_session</code><span class="sig-paren">(</span><em>isolation_level=None</em>, <em>readonly=None</em>, <em>deferrable=None</em>, <em>autocommit=None</em><span class="sig-paren">)</span><a class="headerlink" href="#connection.set_session" title="Permalink to this definition">¶</a></dt>
<dd><p>Set one or more parameters for the next transactions or statements in
the current session.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first last simple">
<li><strong>isolation_level</strong> – set the <a class="reference external" href="http://www.postgresql.org/docs/current/static/transaction-iso.html">isolation level</a> for the next
transactions/statements. The value can be one of the literal
values <code class="docutils literal"><span class="pre">READ</span> <span class="pre">UNCOMMITTED</span></code>, <code class="docutils literal"><span class="pre">READ</span> <span class="pre">COMMITTED</span></code>, <code class="docutils literal"><span class="pre">REPEATABLE</span>
<span class="pre">READ</span></code>, <code class="docutils literal"><span class="pre">SERIALIZABLE</span></code> or the equivalent <a class="reference internal" href="extensions.html#isolation-level-constants"><span>constant</span></a> defined in the <a class="reference internal" href="extensions.html#module-psycopg2.extensions" title="psycopg2.extensions"><code class="xref py py-obj docutils literal"><span class="pre">extensions</span></code></a>
module.</li>
<li><strong>readonly</strong> – if <code class="xref py py-obj docutils literal"><span class="pre">True</span></code>, set the connection to read only;
read/write if <code class="xref py py-obj docutils literal"><span class="pre">False</span></code>.</li>
<li><strong>deferrable</strong> – if <code class="xref py py-obj docutils literal"><span class="pre">True</span></code>, set the connection to deferrable;
non deferrable if <code class="xref py py-obj docutils literal"><span class="pre">False</span></code>. Only available from PostgreSQL 9.1.</li>
<li><strong>autocommit</strong> – switch the connection to autocommit mode: not a
PostgreSQL session setting but an alias for setting the
<a class="reference internal" href="#connection.autocommit" title="connection.autocommit"><code class="xref py py-obj docutils literal"><span class="pre">autocommit</span></code></a> attribute.</li>
</ul>
</td>
</tr>
</tbody>
</table>
<p>Arguments set to <code class="xref py py-obj docutils literal"><span class="pre">None</span></code> (the default for all) will not be changed.
The parameters <em>isolation_level</em>, <em>readonly</em> and <em>deferrable</em> also
accept the string <code class="docutils literal"><span class="pre">DEFAULT</span></code> as a value: the effect is to reset the
parameter to the server default. Defaults are defined by the server
configuration: see values for <a class="reference external" href="http://www.postgresql.org/docs/current/static/runtime-config-client.html#GUC-DEFAULT-TRANSACTION-ISOLATION"><code class="sql docutils literal"><span class="pre">default_transaction_isolation</span></code></a>,
<a class="reference external" href="http://www.postgresql.org/docs/current/static/runtime-config-client.html#GUC-DEFAULT-TRANSACTION-READ-ONLY"><code class="sql docutils literal"><span class="pre">default_transaction_read_only</span></code></a>, <a class="reference external" href="http://www.postgresql.org/docs/current/static/runtime-config-client.html#GUC-DEFAULT-TRANSACTION-DEFERRABLE"><code class="sql docutils literal"><span class="pre">default_transaction_deferrable</span></code></a>.</p>
<p>The function must be invoked with no transaction in progress.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">There is currently no builtin method to read the current value for
the parameters: use <code class="sql docutils literal"><span class="pre">SHOW</span> <span class="pre">default_transaction_...</span></code> to read
the values from the backend.</p>
</div>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last"><a class="reference external" href="http://www.postgresql.org/docs/current/static/sql-set-transaction.html"><code class="sql docutils literal"><span class="pre">SET</span> <span class="pre">TRANSACTION</span></code></a> for further details about the behaviour
of the transaction parameters in the server.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.4.2.</span></p>
</div>
</dd></dl>
<dl class="attribute">
<dt id="connection.autocommit">
<code class="descname">autocommit</code><a class="headerlink" href="#connection.autocommit" title="Permalink to this definition">¶</a></dt>
<dd><p>Read/write attribute: if <code class="xref py py-obj docutils literal"><span class="pre">True</span></code>, no transaction is handled by the
driver and every statement sent to the backend has immediate effect;
if <code class="xref py py-obj docutils literal"><span class="pre">False</span></code> a new transaction is started at the first command
execution: the methods <a class="reference internal" href="#connection.commit" title="connection.commit"><code class="xref py py-obj docutils literal"><span class="pre">commit()</span></code></a> or <a class="reference internal" href="#connection.rollback" title="connection.rollback"><code class="xref py py-obj docutils literal"><span class="pre">rollback()</span></code></a> must be manually
invoked to terminate the transaction.</p>
<p>The autocommit mode is useful to execute commands requiring to be run
outside a transaction, such as <code class="sql docutils literal"><span class="pre">CREATE</span> <span class="pre">DATABASE</span></code> or
<code class="sql docutils literal"><span class="pre">VACUUM</span></code>.</p>
<p>The default is <code class="xref py py-obj docutils literal"><span class="pre">False</span></code> (manual commit) as per DBAPI specification.</p>
<div class="admonition warning">
<p class="first admonition-title">Warning</p>
<p class="last">By default, any query execution, including a simple <code class="sql docutils literal"><span class="pre">SELECT</span></code>
will start a transaction: for long-running programs, if no further
action is taken, the session will remain “idle in transaction”, an
undesirable condition for several reasons (locks are held by
the session, tables bloat...). For long lived scripts, either
ensure to terminate a transaction as soon as possible or use an
autocommit connection.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.4.2.</span></p>
</div>
</dd></dl>
<dl class="attribute">
<dt id="connection.isolation_level">
<code class="descname">isolation_level</code><a class="headerlink" href="#connection.isolation_level" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="connection.set_isolation_level">
<code class="descname">set_isolation_level</code><span class="sig-paren">(</span><em>level</em><span class="sig-paren">)</span><a class="headerlink" href="#connection.set_isolation_level" title="Permalink to this definition">¶</a></dt>
<dd><div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">From version 2.4.2, <a class="reference internal" href="#connection.set_session" title="connection.set_session"><code class="xref py py-obj docutils literal"><span class="pre">set_session()</span></code></a> and <a class="reference internal" href="#connection.autocommit" title="connection.autocommit"><code class="xref py py-obj docutils literal"><span class="pre">autocommit</span></code></a>, offer
finer control on the transaction characteristics.</p>
</div>
<p>Read or set the <a class="reference external" href="http://www.postgresql.org/docs/current/static/transaction-iso.html">transaction isolation level</a> for the current session.
The level defines the different phenomena that can happen in the
database between concurrent transactions.</p>
<p>The value set or read is an integer: symbolic constants are defined in
the module <a class="reference internal" href="extensions.html#module-psycopg2.extensions" title="psycopg2.extensions"><code class="xref py py-obj docutils literal"><span class="pre">psycopg2.extensions</span></code></a>: see
<a class="reference internal" href="extensions.html#isolation-level-constants"><span>Isolation level constants</span></a> for the available values.</p>
<p>The default level is <code class="sql docutils literal"><span class="pre">READ</span> <span class="pre">COMMITTED</span></code>: at this level a
transaction is automatically started the first time a database command
is executed. If you want an <em>autocommit</em> mode, switch to
<a class="reference internal" href="extensions.html#psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT" title="psycopg2.extensions.ISOLATION_LEVEL_AUTOCOMMIT"><code class="xref py py-obj docutils literal"><span class="pre">ISOLATION_LEVEL_AUTOCOMMIT</span></code></a> before
executing any command:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">conn</span><span class="o">.</span><span class="n">set_isolation_level</span><span class="p">(</span><span class="n">psycopg2</span><span class="o">.</span><span class="n">extensions</span><span class="o">.</span><span class="n">ISOLATION_LEVEL_AUTOCOMMIT</span><span class="p">)</span>
</pre></div>
</div>
<p>See also <a class="reference internal" href="usage.html#transactions-control"><span>Transactions control</span></a>.</p>
</dd></dl>
<span class="target" id="index-10"></span><dl class="attribute">
<dt id="connection.encoding">
<code class="descname">encoding</code><a class="headerlink" href="#connection.encoding" title="Permalink to this definition">¶</a></dt>
<dd></dd></dl>
<dl class="method">
<dt id="connection.set_client_encoding">
<code class="descname">set_client_encoding</code><span class="sig-paren">(</span><em>enc</em><span class="sig-paren">)</span><a class="headerlink" href="#connection.set_client_encoding" title="Permalink to this definition">¶</a></dt>
<dd><p>Read or set the client encoding for the current session. The default
is the encoding defined by the database. It should be one of the
<a class="reference external" href="http://www.postgresql.org/docs/current/static/multibyte.html">characters set supported by PostgreSQL</a></p>
</dd></dl>
<span class="target" id="index-11"></span><dl class="attribute">
<dt id="connection.notices">
<code class="descname">notices</code><a class="headerlink" href="#connection.notices" title="Permalink to this definition">¶</a></dt>
<dd><p>A list containing all the database messages sent to the client during
the session.</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">cur</span><span class="o">.</span><span class="n">execute</span><span class="p">(</span><span class="s">"CREATE TABLE foo (id serial PRIMARY KEY);"</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">pprint</span><span class="p">(</span><span class="n">conn</span><span class="o">.</span><span class="n">notices</span><span class="p">)</span>
<span class="go">['NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "foo_pkey" for table "foo"\n',</span>
<span class="go"> 'NOTICE: CREATE TABLE will create implicit sequence "foo_id_seq" for serial column "foo.id"\n']</span>
</pre></div>
</div>
<p>To avoid a leak in case excessive notices are generated, only the last
50 messages are kept.</p>
<p>You can configure what messages to receive using <a class="reference external" href="http://www.postgresql.org/docs/current/static/runtime-config-logging.html">PostgreSQL logging
configuration parameters</a> such as <code class="docutils literal"><span class="pre">log_statement</span></code>,
<code class="docutils literal"><span class="pre">client_min_messages</span></code>, <code class="docutils literal"><span class="pre">log_min_duration_statement</span></code> etc.</p>
</dd></dl>
<dl class="attribute">
<dt id="connection.notifies">
<code class="descname">notifies</code><a class="headerlink" href="#connection.notifies" title="Permalink to this definition">¶</a></dt>
<dd><p>List of <code class="xref py py-obj docutils literal"><span class="pre">Notify</span></code> objects containing asynchronous
notifications received by the session.</p>
<p>For other details see <a class="reference internal" href="advanced.html#async-notify"><span>Asynchronous notifications</span></a>.</p>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.3: </span>Notifications are instances of the <code class="xref py py-obj docutils literal"><span class="pre">Notify</span></code> object. Previously the
list was composed by 2 items tuples <code class="samp docutils literal"><span class="pre">(</span><em><span class="pre">pid</span></em><span class="pre">,</span><em><span class="pre">channel</span></em><span class="pre">)</span></code> and
the payload was not accessible. To keep backward compatibility,
<code class="xref py py-obj docutils literal"><span class="pre">Notify</span></code> objects can still be accessed as 2 items tuples.</p>
</div>
</dd></dl>
<dl class="attribute">
<dt id="connection.cursor_factory">
<code class="descname">cursor_factory</code><a class="headerlink" href="#connection.cursor_factory" title="Permalink to this definition">¶</a></dt>
<dd><p>The default cursor factory used by <a class="reference internal" href="#connection.cursor" title="connection.cursor"><code class="xref py py-obj docutils literal"><span class="pre">cursor()</span></code></a> if the
parameter is not specified.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.5.</span></p>
</div>
</dd></dl>
<span class="target" id="index-12"></span><dl class="method">
<dt id="connection.get_backend_pid">
<code class="descname">get_backend_pid</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.get_backend_pid" title="Permalink to this definition">¶</a></dt>
<dd><p>Returns the process ID (PID) of the backend server process handling
this connection.</p>
<p>Note that the PID belongs to a process executing on the database
server host, not the local host!</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">libpq docs for <a class="reference external" href="http://www.postgresql.org/docs/current/static/libpq-status.html#LIBPQ-PQBACKENDPID">PQbackendPID()</a> for details.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.0.8.</span></p>
</div>
</dd></dl>
<span class="target" id="index-13"></span><dl class="method">
<dt id="connection.get_parameter_status">
<code class="descname">get_parameter_status</code><span class="sig-paren">(</span><em>parameter</em><span class="sig-paren">)</span><a class="headerlink" href="#connection.get_parameter_status" title="Permalink to this definition">¶</a></dt>
<dd><p>Look up a current parameter setting of the server.</p>
<p>Potential values for <code class="docutils literal"><span class="pre">parameter</span></code> are: <code class="docutils literal"><span class="pre">server_version</span></code>,
<code class="docutils literal"><span class="pre">server_encoding</span></code>, <code class="docutils literal"><span class="pre">client_encoding</span></code>, <code class="docutils literal"><span class="pre">is_superuser</span></code>,
<code class="docutils literal"><span class="pre">session_authorization</span></code>, <code class="docutils literal"><span class="pre">DateStyle</span></code>, <code class="docutils literal"><span class="pre">TimeZone</span></code>,
<code class="docutils literal"><span class="pre">integer_datetimes</span></code>, and <code class="docutils literal"><span class="pre">standard_conforming_strings</span></code>.</p>
<p>If server did not report requested parameter, return <code class="xref py py-obj docutils literal"><span class="pre">None</span></code>.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">libpq docs for <a class="reference external" href="http://www.postgresql.org/docs/current/static/libpq-status.html#LIBPQ-PQPARAMETERSTATUS">PQparameterStatus()</a> for details.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.0.12.</span></p>
</div>
</dd></dl>
<span class="target" id="index-14"></span><dl class="method">
<dt id="connection.get_transaction_status">
<code class="descname">get_transaction_status</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.get_transaction_status" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current session transaction status as an integer. Symbolic
constants for the values are defined in the module
<a class="reference internal" href="extensions.html#module-psycopg2.extensions" title="psycopg2.extensions"><code class="xref py py-obj docutils literal"><span class="pre">psycopg2.extensions</span></code></a>: see <a class="reference internal" href="extensions.html#transaction-status-constants"><span>Transaction status constants</span></a>
for the available values.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">libpq docs for <a class="reference external" href="http://www.postgresql.org/docs/current/static/libpq-status.html#LIBPQ-PQTRANSACTIONSTATUS">PQtransactionStatus()</a> for details.</p>
</div>
</dd></dl>
<span class="target" id="index-15"></span><dl class="attribute">
<dt id="connection.protocol_version">
<code class="descname">protocol_version</code><a class="headerlink" href="#connection.protocol_version" title="Permalink to this definition">¶</a></dt>
<dd><p>A read-only integer representing frontend/backend protocol being used.
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.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">libpq docs for <a class="reference external" href="http://www.postgresql.org/docs/current/static/libpq-status.html#LIBPQ-PQPROTOCOLVERSION">PQprotocolVersion()</a> for details.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.0.12.</span></p>
</div>
</dd></dl>
<span class="target" id="index-16"></span><dl class="attribute">
<dt id="connection.server_version">
<code class="descname">server_version</code><a class="headerlink" href="#connection.server_version" title="Permalink to this definition">¶</a></dt>
<dd><p>A read-only integer representing the backend version.</p>
<p>The number is formed by converting the major, minor, and revision
numbers into two-decimal-digit numbers and appending them together.
For example, version 8.1.5 will be returned as <code class="docutils literal"><span class="pre">80105</span></code>.</p>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last">libpq docs for <a class="reference external" href="http://www.postgresql.org/docs/current/static/libpq-status.html#LIBPQ-PQSERVERVERSION">PQserverVersion()</a> for details.</p>
</div>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.0.12.</span></p>
</div>
</dd></dl>
<span class="target" id="index-17"></span><dl class="attribute">
<dt id="connection.status">
<code class="descname">status</code><a class="headerlink" href="#connection.status" title="Permalink to this definition">¶</a></dt>
<dd><p>A read-only integer representing the status of the connection.
Symbolic constants for the values are defined in the module
<a class="reference internal" href="extensions.html#module-psycopg2.extensions" title="psycopg2.extensions"><code class="xref py py-obj docutils literal"><span class="pre">psycopg2.extensions</span></code></a>: see <a class="reference internal" href="extensions.html#connection-status-constants"><span>Connection status constants</span></a>
for the available values.</p>
<p>The status is undefined for <a class="reference internal" href="#connection.closed" title="connection.closed"><code class="xref py py-obj docutils literal"><span class="pre">closed</span></code></a> connectons.</p>
</dd></dl>
<dl class="method">
<dt id="connection.lobject">
<code class="descname">lobject</code><span class="sig-paren">(</span><span class="optional">[</span><em>oid</em><span class="optional">[</span>, <em>mode</em><span class="optional">[</span>, <em>new_oid</em><span class="optional">[</span>, <em>new_file</em><span class="optional">[</span>, <em>lobject_factory</em><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.lobject" title="Permalink to this definition">¶</a></dt>
<dd><p>Return a new database large object as a <a class="reference internal" href="extensions.html#psycopg2.extensions.lobject" title="psycopg2.extensions.lobject"><code class="xref py py-obj docutils literal"><span class="pre">lobject</span></code></a>
instance.</p>
<p>See <a class="reference internal" href="usage.html#large-objects"><span>Access to PostgreSQL large objects</span></a> for an overview.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first last simple">
<li><strong>oid</strong> – The OID of the object to read or write. 0 to create
a new large object and and have its OID assigned automatically.</li>
<li><strong>mode</strong> – Access mode to the object, see below.</li>
<li><strong>new_oid</strong> – Create a new object using the specified OID. The
function raises <a class="reference internal" href="module.html#psycopg2.OperationalError" title="psycopg2.OperationalError"><code class="xref py py-obj docutils literal"><span class="pre">OperationalError</span></code></a> if the OID is already
in use. Default is 0, meaning assign a new one automatically.</li>
<li><strong>new_file</strong> – The name of a file to be imported in the the database
(using the <a class="reference external" href="http://www.postgresql.org/docs/current/static/lo-interfaces.html#LO-IMPORT"><code class="xref py py-obj docutils literal"><span class="pre">lo_import()</span></code></a> function)</li>
<li><strong>lobject_factory</strong> – Subclass of
<a class="reference internal" href="extensions.html#psycopg2.extensions.lobject" title="psycopg2.extensions.lobject"><code class="xref py py-obj docutils literal"><span class="pre">lobject</span></code></a> to be instantiated.</li>
</ul>
</td>
</tr>
</tbody>
</table>
<p>Available values for <em>mode</em> are:</p>
<table border="1" class="docutils">
<colgroup>
<col width="6%" />
<col width="94%" />
</colgroup>
<thead valign="bottom">
<tr class="row-odd"><th class="head"><em>mode</em></th>
<th class="head">meaning</th>
</tr>
</thead>
<tbody valign="top">
<tr class="row-even"><td><code class="docutils literal"><span class="pre">r</span></code></td>
<td>Open for read only</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal"><span class="pre">w</span></code></td>
<td>Open for write only</td>
</tr>
<tr class="row-even"><td><code class="docutils literal"><span class="pre">rw</span></code></td>
<td>Open for read/write</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal"><span class="pre">n</span></code></td>
<td>Don’t open the file</td>
</tr>
<tr class="row-even"><td><code class="docutils literal"><span class="pre">b</span></code></td>
<td>Don’t decode read data (return data as <code class="xref py py-obj docutils literal"><span class="pre">str</span></code> in Python 2 or <code class="xref py py-obj docutils literal"><span class="pre">bytes</span></code> in Python 3)</td>
</tr>
<tr class="row-odd"><td><code class="docutils literal"><span class="pre">t</span></code></td>
<td>Decode read data according to <a class="reference internal" href="#connection.encoding" title="connection.encoding"><code class="xref py py-obj docutils literal"><span class="pre">connection.encoding</span></code></a> (return data as <code class="xref py py-obj docutils literal"><span class="pre">unicode</span></code> in Python 2 or <code class="xref py py-obj docutils literal"><span class="pre">str</span></code> in Python 3)</td>
</tr>
</tbody>
</table>
<p><code class="docutils literal"><span class="pre">b</span></code> and <code class="docutils literal"><span class="pre">t</span></code> can be specified together with a read/write mode. If
neither <code class="docutils literal"><span class="pre">b</span></code> nor <code class="docutils literal"><span class="pre">t</span></code> is specified, the default is <code class="docutils literal"><span class="pre">b</span></code> in Python 2
and <code class="docutils literal"><span class="pre">t</span></code> in Python 3.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.0.8.</span></p>
</div>
<div class="versionchanged">
<p><span class="versionmodified">Changed in version 2.4: </span>added <code class="docutils literal"><span class="pre">b</span></code> and <code class="docutils literal"><span class="pre">t</span></code> mode and unicode
support.</p>
</div>
</dd></dl>
<p class="rubric">Methods related to asynchronous support.</p>
<div class="versionadded">
<p><span class="versionmodified">New in version 2.2.0.</span></p>
</div>
<div class="admonition seealso">
<p class="first admonition-title">See also</p>
<p class="last"><a class="reference internal" href="advanced.html#async-support"><span>Asynchronous support</span></a> and <a class="reference internal" href="advanced.html#green-support"><span>Support for coroutine libraries</span></a>.</p>
</div>
<dl class="attribute">
<dt id="connection.async">
<code class="descname">async</code><a class="headerlink" href="#connection.async" title="Permalink to this definition">¶</a></dt>
<dd><p>Read only attribute: 1 if the connection is asynchronous, 0 otherwise.</p>
</dd></dl>
<dl class="method">
<dt id="connection.poll">
<code class="descname">poll</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.poll" title="Permalink to this definition">¶</a></dt>
<dd><p>Used during an asynchronous connection attempt, or when a cursor is
executing a query on an asynchronous connection, make communication
proceed if it wouldn’t block.</p>
<p>Return one of the constants defined in <a class="reference internal" href="extensions.html#poll-constants"><span>Poll constants</span></a>. If it
returns <a class="reference internal" href="extensions.html#psycopg2.extensions.POLL_OK" title="psycopg2.extensions.POLL_OK"><code class="xref py py-obj docutils literal"><span class="pre">POLL_OK</span></code></a> then the connection has been
established or the query results are available on the client.
Otherwise wait until the file descriptor returned by <a class="reference internal" href="#connection.fileno" title="connection.fileno"><code class="xref py py-obj docutils literal"><span class="pre">fileno()</span></code></a> is
ready to read or to write, as explained in <a class="reference internal" href="advanced.html#async-support"><span>Asynchronous support</span></a>.
<a class="reference internal" href="#connection.poll" title="connection.poll"><code class="xref py py-obj docutils literal"><span class="pre">poll()</span></code></a> should be also used by the function installed by
<code class="xref py py-obj docutils literal"><span class="pre">set_wait_callback()</span></code> as explained in
<a class="reference internal" href="advanced.html#green-support"><span>Support for coroutine libraries</span></a>.</p>
<p><a class="reference internal" href="#connection.poll" title="connection.poll"><code class="xref py py-obj docutils literal"><span class="pre">poll()</span></code></a> is also used to receive asynchronous notifications from the
database: see <a class="reference internal" href="advanced.html#async-notify"><span>Asynchronous notifications</span></a> from further details.</p>
</dd></dl>
<dl class="method">
<dt id="connection.fileno">
<code class="descname">fileno</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.fileno" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the file descriptor underlying the connection: useful to read
its status during asynchronous communication.</p>
</dd></dl>
<dl class="method">
<dt id="connection.isexecuting">
<code class="descname">isexecuting</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#connection.isexecuting" title="Permalink to this definition">¶</a></dt>
<dd><p>Return <code class="xref py py-obj docutils literal"><span class="pre">True</span></code> if the connection is executing an asynchronous operation.</p>
</dd></dl>
</dd></dl>
</div>
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