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 <div class="section" id="module-logging.config">
<h1>16.7. <a class="reference internal" href="#module-logging.config" title="logging.config: Configuration of the logging module."><code class="xref py py-mod docutils literal notranslate">logging.config</code></a> — Logging configuration<a class="headerlink" href="#module-logging.config" title="Permalink to this headline">¶</a></h1>
Source code: <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/logging/config.py">Lib/logging/config.py</a>
<div class="sidebar">
Important
This page contains only reference information. For tutorials,
please see
<ul class="last simple">
<li><a class="reference internal" href="../howto/logging.html#logging-basic-tutorial">Basic Tutorial</a></li>
<li><a class="reference internal" href="../howto/logging.html#logging-advanced-tutorial">Advanced Tutorial</a></li>
<li><a class="reference internal" href="../howto/logging-cookbook.html#logging-cookbook">Logging Cookbook</a></li>
</ul>
</div>
<hr class="docutils" />
This section describes the API for configuring the logging module.
<div class="section" id="configuration-functions">
<h2>16.7.1. Configuration functions<a class="headerlink" href="#configuration-functions" title="Permalink to this headline">¶</a></h2>
The following functions configure the logging module. They are located in the
<a class="reference internal" href="#module-logging.config" title="logging.config: Configuration of the logging module."><code class="xref py py-mod docutils literal notranslate">logging.config</code></a> module. Their use is optional — you can configure the
logging module using these functions or by making calls to the main API (defined
in <a class="reference internal" href="logging.html#module-logging" title="logging: Flexible event logging system for applications."><code class="xref py py-mod docutils literal notranslate">logging</code></a> itself) and defining handlers which are declared either in
<a class="reference internal" href="logging.html#module-logging" title="logging: Flexible event logging system for applications."><code class="xref py py-mod docutils literal notranslate">logging</code></a> or <a class="reference internal" href="logging.handlers.html#module-logging.handlers" title="logging.handlers: Handlers for the logging module."><code class="xref py py-mod docutils literal notranslate">logging.handlers</code></a>.
<dl class="function">
<dt id="logging.config.dictConfig">
<code class="descclassname">logging.config.</code><code class="descname">dictConfig</code>(config)<a class="headerlink" href="#logging.config.dictConfig" title="Permalink to this definition">¶</a></dt>
<dd><blockquote>
<div>Takes the logging configuration from a dictionary. The contents of
this dictionary are described in <a class="reference internal" href="#logging-config-dictschema">Configuration dictionary schema</a>
below.
If an error is encountered during configuration, this function will
raise a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate">ValueError</code></a>, <a class="reference internal" href="exceptions.html#TypeError" title="TypeError"><code class="xref py py-exc docutils literal notranslate">TypeError</code></a>, <a class="reference internal" href="exceptions.html#AttributeError" title="AttributeError"><code class="xref py py-exc docutils literal notranslate">AttributeError</code></a>
or <a class="reference internal" href="exceptions.html#ImportError" title="ImportError"><code class="xref py py-exc docutils literal notranslate">ImportError</code></a> with a suitably descriptive message. The
following is a (possibly incomplete) list of conditions which will
raise an error:
<ul class="simple">
<li>A <code class="docutils literal notranslate">level</code> which is not a string or which is a string not
corresponding to an actual logging level.</li>
<li>A <code class="docutils literal notranslate">propagate</code> value which is not a boolean.</li>
<li>An id which does not have a corresponding destination.</li>
<li>A non-existent handler id found during an incremental call.</li>
<li>An invalid logger name.</li>
<li>Inability to resolve to an internal or external object.</li>
</ul>
Parsing is performed by the <code class="xref py py-class docutils literal notranslate">DictConfigurator</code> class, whose
constructor is passed the dictionary used for configuration, and
has a <code class="xref py py-meth docutils literal notranslate">configure()</code> method. The <a class="reference internal" href="#module-logging.config" title="logging.config: Configuration of the logging module."><code class="xref py py-mod docutils literal notranslate">logging.config</code></a> module
has a callable attribute <code class="xref py py-attr docutils literal notranslate">dictConfigClass</code>
which is initially set to <code class="xref py py-class docutils literal notranslate">DictConfigurator</code>.
You can replace the value of <code class="xref py py-attr docutils literal notranslate">dictConfigClass</code> with a
suitable implementation of your own.
<a class="reference internal" href="#logging.config.dictConfig" title="logging.config.dictConfig"><code class="xref py py-func docutils literal notranslate">dictConfig()</code></a> calls <code class="xref py py-attr docutils literal notranslate">dictConfigClass</code> passing
the specified dictionary, and then calls the <code class="xref py py-meth docutils literal notranslate">configure()</code> method on
the returned object to put the configuration into effect:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>def dictConfig(config):
 dictConfigClass(config).configure()
</pre></div>
</div>
For example, a subclass of <code class="xref py py-class docutils literal notranslate">DictConfigurator</code> could call
<code class="docutils literal notranslate">DictConfigurator.__init__()</code> in its own <a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate">__init__()</code></a>, then
set up custom prefixes which would be usable in the subsequent
<code class="xref py py-meth docutils literal notranslate">configure()</code> call. <code class="xref py py-attr docutils literal notranslate">dictConfigClass</code> would be bound to
this new subclass, and then <a class="reference internal" href="#logging.config.dictConfig" title="logging.config.dictConfig"><code class="xref py py-func docutils literal notranslate">dictConfig()</code></a> could be called exactly as
in the default, uncustomized state.
</div></blockquote>
<div class="versionadded">
New in version 3.2.
</div>
</dd></dl>

<dl class="function">
<dt id="logging.config.fileConfig">
<code class="descclassname">logging.config.</code><code class="descname">fileConfig</code>(fname, defaults=None, disable_existing_loggers=True)<a class="headerlink" href="#logging.config.fileConfig" title="Permalink to this definition">¶</a></dt>
<dd>Reads the logging configuration from a <a class="reference internal" href="configparser.html#module-configparser" title="configparser: Configuration file parser."><code class="xref py py-mod docutils literal notranslate">configparser</code></a>-format file. The
format of the file should be as described in
<a class="reference internal" href="#logging-config-fileformat">Configuration file format</a>.
This function can be called several times from an application, allowing an
end user to select from various pre-canned configurations (if the developer
provides a mechanism to present the choices and load the chosen
configuration).
<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>fname – A filename, or a file-like object, or an instance derived
from <a class="reference internal" href="configparser.html#configparser.RawConfigParser" title="configparser.RawConfigParser"><code class="xref py py-class docutils literal notranslate">RawConfigParser</code></a>. If a
<code class="docutils literal notranslate">RawConfigParser</code>-derived instance is passed, it is used as
is. Otherwise, a <code class="xref py py-class docutils literal notranslate">Configparser</code> is
instantiated, and the configuration read by it from the
object passed in <code class="docutils literal notranslate">fname</code>. If that has a <a class="reference internal" href="readline.html#module-readline" title="readline: GNU readline support for Python. (Unix)"><code class="xref py py-meth docutils literal notranslate">readline()</code></a>
method, it is assumed to be a file-like object and read using
<a class="reference internal" href="configparser.html#configparser.ConfigParser.read_file" title="configparser.ConfigParser.read_file"><code class="xref py py-meth docutils literal notranslate">read_file()</code></a>; otherwise,
it is assumed to be a filename and passed to
<a class="reference internal" href="configparser.html#configparser.ConfigParser.read" title="configparser.ConfigParser.read"><code class="xref py py-meth docutils literal notranslate">read()</code></a>.</li>
<li>defaults – Defaults to be passed to the ConfigParser can be specified
in this argument.</li>
<li>disable_existing_loggers – If specified as <code class="docutils literal notranslate">False</code>, loggers which
exist when this call is made are left
enabled. The default is <code class="docutils literal notranslate">True</code> because this
enables old behaviour in a
backward-compatible way. This behaviour is to
disable any existing loggers unless they or
their ancestors are explicitly named in the
logging configuration.</li>
</ul>
</td>
</tr>
</tbody>
</table>
<div class="versionchanged">
Changed in version 3.4: An instance of a subclass of <a class="reference internal" href="configparser.html#configparser.RawConfigParser" title="configparser.RawConfigParser"><code class="xref py py-class docutils literal notranslate">RawConfigParser</code></a> is
now accepted as a value for <code class="docutils literal notranslate">fname</code>. This facilitates:
<ul class="simple">
<li>Use of a configuration file where logging configuration is just part
of the overall application configuration.</li>
<li>Use of a configuration read from a file, and then modified by the using
application (e.g. based on command-line parameters or other aspects
of the runtime environment) before being passed to <code class="docutils literal notranslate">fileConfig</code>.</li>
</ul>
</div>
</dd></dl>

<dl class="function">
<dt id="logging.config.listen">
<code class="descclassname">logging.config.</code><code class="descname">listen</code>(port=DEFAULT_LOGGING_CONFIG_PORT, verify=None)<a class="headerlink" href="#logging.config.listen" title="Permalink to this definition">¶</a></dt>
<dd>Starts up a socket server on the specified port, and listens for new
configurations. If no port is specified, the module’s default
<code class="xref py py-const docutils literal notranslate">DEFAULT_LOGGING_CONFIG_PORT</code> is used. Logging configurations will be
sent as a file suitable for processing by <a class="reference internal" href="#logging.config.dictConfig" title="logging.config.dictConfig"><code class="xref py py-func docutils literal notranslate">dictConfig()</code></a> or
<a class="reference internal" href="#logging.config.fileConfig" title="logging.config.fileConfig"><code class="xref py py-func docutils literal notranslate">fileConfig()</code></a>. Returns a <a class="reference internal" href="threading.html#threading.Thread" title="threading.Thread"><code class="xref py py-class docutils literal notranslate">Thread</code></a> instance on which
you can call <a class="reference internal" href="threading.html#threading.Thread.start" title="threading.Thread.start"><code class="xref py py-meth docutils literal notranslate">start()</code></a> to start the server, and which
you can <a class="reference internal" href="threading.html#threading.Thread.join" title="threading.Thread.join"><code class="xref py py-meth docutils literal notranslate">join()</code></a> when appropriate. To stop the server,
call <a class="reference internal" href="#logging.config.stopListening" title="logging.config.stopListening"><code class="xref py py-func docutils literal notranslate">stopListening()</code></a>.
The <code class="docutils literal notranslate">verify</code> argument, if specified, should be a callable which should
verify whether bytes received across the socket are valid and should be
processed. This could be done by encrypting and/or signing what is sent
across the socket, such that the <code class="docutils literal notranslate">verify</code> callable can perform
signature verification and/or decryption. The <code class="docutils literal notranslate">verify</code> callable is called
with a single argument - the bytes received across the socket - and should
return the bytes to be processed, or <code class="docutils literal notranslate">None</code> to indicate that the bytes should
be discarded. The returned bytes could be the same as the passed in bytes
(e.g. when only verification is done), or they could be completely different
(perhaps if decryption were performed).
To send a configuration to the socket, read in the configuration file and
send it to the socket as a sequence of bytes preceded by a four-byte length
string packed in binary using <code class="docutils literal notranslate">struct.pack('&gt;L', n)</code>.
<div class="admonition note">
Note
Because portions of the configuration are passed through
<a class="reference internal" href="functions.html#eval" title="eval"><code class="xref py py-func docutils literal notranslate">eval()</code></a>, use of this function may open its users to a security risk.
While the function only binds to a socket on <code class="docutils literal notranslate">localhost</code>, and so does
not accept connections from remote machines, there are scenarios where
untrusted code could be run under the account of the process which calls
<a class="reference internal" href="#logging.config.listen" title="logging.config.listen"><code class="xref py py-func docutils literal notranslate">listen()</code></a>. Specifically, if the process calling <a class="reference internal" href="#logging.config.listen" title="logging.config.listen"><code class="xref py py-func docutils literal notranslate">listen()</code></a> runs
on a multi-user machine where users cannot trust each other, then a
malicious user could arrange to run essentially arbitrary code in a
victim user’s process, simply by connecting to the victim’s
<a class="reference internal" href="#logging.config.listen" title="logging.config.listen"><code class="xref py py-func docutils literal notranslate">listen()</code></a> socket and sending a configuration which runs whatever
code the attacker wants to have executed in the victim’s process. This is
especially easy to do if the default port is used, but not hard even if a
different port is used). To avoid the risk of this happening, use the
<code class="docutils literal notranslate">verify</code> argument to <a class="reference internal" href="#logging.config.listen" title="logging.config.listen"><code class="xref py py-func docutils literal notranslate">listen()</code></a> to prevent unrecognised
configurations from being applied.
</div>
<div class="versionchanged">
Changed in version 3.4: The <code class="docutils literal notranslate">verify</code> argument was added.
</div>
<div class="admonition note">
Note
If you want to send configurations to the listener which don’t
disable existing loggers, you will need to use a JSON format for
the configuration, which will use <a class="reference internal" href="#logging.config.dictConfig" title="logging.config.dictConfig"><code class="xref py py-func docutils literal notranslate">dictConfig()</code></a> for configuration.
This method allows you to specify <code class="docutils literal notranslate">disable_existing_loggers</code> as
<code class="docutils literal notranslate">False</code> in the configuration you send.
</div>
</dd></dl>

<dl class="function">
<dt id="logging.config.stopListening">
<code class="descclassname">logging.config.</code><code class="descname">stopListening</code>()<a class="headerlink" href="#logging.config.stopListening" title="Permalink to this definition">¶</a></dt>
<dd>Stops the listening server which was created with a call to <a class="reference internal" href="#logging.config.listen" title="logging.config.listen"><code class="xref py py-func docutils literal notranslate">listen()</code></a>.
This is typically called before calling <code class="xref py py-meth docutils literal notranslate">join()</code> on the return value from
<a class="reference internal" href="#logging.config.listen" title="logging.config.listen"><code class="xref py py-func docutils literal notranslate">listen()</code></a>.
</dd></dl>

</div>
<div class="section" id="configuration-dictionary-schema">
<h2>16.7.2. Configuration dictionary schema<a class="headerlink" href="#configuration-dictionary-schema" title="Permalink to this headline">¶</a></h2>
Describing a logging configuration requires listing the various
objects to create and the connections between them; for example, you
may create a handler named ‘console’ and then say that the logger
named ‘startup’ will send its messages to the ‘console’ handler.
These objects aren’t limited to those provided by the <a class="reference internal" href="logging.html#module-logging" title="logging: Flexible event logging system for applications."><code class="xref py py-mod docutils literal notranslate">logging</code></a>
module because you might write your own formatter or handler class.
The parameters to these classes may also need to include external
objects such as <code class="docutils literal notranslate">sys.stderr</code>. The syntax for describing these
objects and connections is defined in <a class="reference internal" href="#logging-config-dict-connections">Object connections</a>
below.
<div class="section" id="dictionary-schema-details">
<h3>16.7.2.1. Dictionary Schema Details<a class="headerlink" href="#dictionary-schema-details" title="Permalink to this headline">¶</a></h3>
The dictionary passed to <a class="reference internal" href="#logging.config.dictConfig" title="logging.config.dictConfig"><code class="xref py py-func docutils literal notranslate">dictConfig()</code></a> must contain the following
keys:
<ul class="simple">
<li>version - to be set to an integer value representing the schema
version. The only valid value at present is 1, but having this key
allows the schema to evolve while still preserving backwards
compatibility.</li>
</ul>
All other keys are optional, but if present they will be interpreted
as described below. In all cases below where a ‘configuring dict’ is
mentioned, it will be checked for the special <code class="docutils literal notranslate">'()'</code> key to see if a
custom instantiation is required. If so, the mechanism described in
<a class="reference internal" href="#logging-config-dict-userdef">User-defined objects</a> below is used to create an instance;
otherwise, the context is used to determine what to instantiate.
<ul>
<li>formatters - the corresponding value will be a dict in which each
key is a formatter id and each value is a dict describing how to
configure the corresponding <a class="reference internal" href="logging.html#logging.Formatter" title="logging.Formatter"><code class="xref py py-class docutils literal notranslate">Formatter</code></a> instance.
The configuring dict is searched for keys <code class="docutils literal notranslate">format</code> and <code class="docutils literal notranslate">datefmt</code>
(with defaults of <code class="docutils literal notranslate">None</code>) and these are used to construct a
<a class="reference internal" href="logging.html#logging.Formatter" title="logging.Formatter"><code class="xref py py-class docutils literal notranslate">Formatter</code></a> instance.
</li>
<li>filters - the corresponding value will be a dict in which each key
is a filter id and each value is a dict describing how to configure
the corresponding Filter instance.
The configuring dict is searched for the key <code class="docutils literal notranslate">name</code> (defaulting to the
empty string) and this is used to construct a <a class="reference internal" href="logging.html#logging.Filter" title="logging.Filter"><code class="xref py py-class docutils literal notranslate">logging.Filter</code></a>
instance.
</li>
<li>handlers - the corresponding value will be a dict in which each
key is a handler id and each value is a dict describing how to
configure the corresponding Handler instance.
The configuring dict is searched for the following keys:
<ul class="simple">
<li><code class="docutils literal notranslate">class</code> (mandatory). This is the fully qualified name of the
handler class.</li>
<li><code class="docutils literal notranslate">level</code> (optional). The level of the handler.</li>
<li><code class="docutils literal notranslate">formatter</code> (optional). The id of the formatter for this
handler.</li>
<li><code class="docutils literal notranslate">filters</code> (optional). A list of ids of the filters for this
handler.</li>
</ul>
All other keys are passed through as keyword arguments to the
handler’s constructor. For example, given the snippet:
<div class="highlight-yaml notranslate"><div class="highlight"><pre>handlers:
 console:
 class : logging.StreamHandler
 formatter: brief
 level : INFO
 filters: [allow_foo]
 stream : ext://sys.stdout
 file:
 class : logging.handlers.RotatingFileHandler
 formatter: precise
 filename: logconfig.log
 maxBytes: 1024
 backupCount: 3
</pre></div>
</div>
the handler with id <code class="docutils literal notranslate">console</code> is instantiated as a
<a class="reference internal" href="logging.handlers.html#logging.StreamHandler" title="logging.StreamHandler"><code class="xref py py-class docutils literal notranslate">logging.StreamHandler</code></a>, using <code class="docutils literal notranslate">sys.stdout</code> as the underlying
stream. The handler with id <code class="docutils literal notranslate">file</code> is instantiated as a
<a class="reference internal" href="logging.handlers.html#logging.handlers.RotatingFileHandler" title="logging.handlers.RotatingFileHandler"><code class="xref py py-class docutils literal notranslate">logging.handlers.RotatingFileHandler</code></a> with the keyword arguments
<code class="docutils literal notranslate">filename='logconfig.log', maxBytes=1024, backupCount=3</code>.
</li>
<li>loggers - the corresponding value will be a dict in which each key
is a logger name and each value is a dict describing how to
configure the corresponding Logger instance.
The configuring dict is searched for the following keys:
<ul class="simple">
<li><code class="docutils literal notranslate">level</code> (optional). The level of the logger.</li>
<li><code class="docutils literal notranslate">propagate</code> (optional). The propagation setting of the logger.</li>
<li><code class="docutils literal notranslate">filters</code> (optional). A list of ids of the filters for this
logger.</li>
<li><code class="docutils literal notranslate">handlers</code> (optional). A list of ids of the handlers for this
logger.</li>
</ul>
The specified loggers will be configured according to the level,
propagation, filters and handlers specified.
</li>
<li>root - this will be the configuration for the root logger.
Processing of the configuration will be as for any logger, except
that the <code class="docutils literal notranslate">propagate</code> setting will not be applicable.
</li>
<li>incremental - whether the configuration is to be interpreted as
incremental to the existing configuration. This value defaults to
<code class="docutils literal notranslate">False</code>, which means that the specified configuration replaces the
existing configuration with the same semantics as used by the
existing <a class="reference internal" href="#logging.config.fileConfig" title="logging.config.fileConfig"><code class="xref py py-func docutils literal notranslate">fileConfig()</code></a> API.
If the specified value is <code class="docutils literal notranslate">True</code>, the configuration is processed
as described in the section on <a class="reference internal" href="#logging-config-dict-incremental">Incremental Configuration</a>.
</li>
<li>disable_existing_loggers - whether any existing loggers are to be
disabled. This setting mirrors the parameter of the same name in
<a class="reference internal" href="#logging.config.fileConfig" title="logging.config.fileConfig"><code class="xref py py-func docutils literal notranslate">fileConfig()</code></a>. If absent, this parameter defaults to <code class="docutils literal notranslate">True</code>.
This value is ignored if incremental is <code class="docutils literal notranslate">True</code>.
</li>
</ul>
</div>
<div class="section" id="incremental-configuration">
<h3>16.7.2.2. Incremental Configuration<a class="headerlink" href="#incremental-configuration" title="Permalink to this headline">¶</a></h3>
It is difficult to provide complete flexibility for incremental
configuration. For example, because objects such as filters
and formatters are anonymous, once a configuration is set up, it is
not possible to refer to such anonymous objects when augmenting a
configuration.
Furthermore, there is not a compelling case for arbitrarily altering
the object graph of loggers, handlers, filters, formatters at
run-time, once a configuration is set up; the verbosity of loggers and
handlers can be controlled just by setting levels (and, in the case of
loggers, propagation flags). Changing the object graph arbitrarily in
a safe way is problematic in a multi-threaded environment; while not
impossible, the benefits are not worth the complexity it adds to the
implementation.
Thus, when the <code class="docutils literal notranslate">incremental</code> key of a configuration dict is present
and is <code class="docutils literal notranslate">True</code>, the system will completely ignore any <code class="docutils literal notranslate">formatters</code> and
<code class="docutils literal notranslate">filters</code> entries, and process only the <code class="docutils literal notranslate">level</code>
settings in the <code class="docutils literal notranslate">handlers</code> entries, and the <code class="docutils literal notranslate">level</code> and
<code class="docutils literal notranslate">propagate</code> settings in the <code class="docutils literal notranslate">loggers</code> and <code class="docutils literal notranslate">root</code> entries.
Using a value in the configuration dict lets configurations to be sent
over the wire as pickled dicts to a socket listener. Thus, the logging
verbosity of a long-running application can be altered over time with
no need to stop and restart the application.
</div>
<div class="section" id="object-connections">
<h3>16.7.2.3. Object connections<a class="headerlink" href="#object-connections" title="Permalink to this headline">¶</a></h3>
The schema describes a set of logging objects - loggers,
handlers, formatters, filters - which are connected to each other in
an object graph. Thus, the schema needs to represent connections
between the objects. For example, say that, once configured, a
particular logger has attached to it a particular handler. For the
purposes of this discussion, we can say that the logger represents the
source, and the handler the destination, of a connection between the
two. Of course in the configured objects this is represented by the
logger holding a reference to the handler. In the configuration dict,
this is done by giving each destination object an id which identifies
it unambiguously, and then using the id in the source object’s
configuration to indicate that a connection exists between the source
and the destination object with that id.
So, for example, consider the following YAML snippet:
<div class="highlight-yaml notranslate"><div class="highlight"><pre>formatters:
 brief:
 # configuration for formatter with id &#39;brief&#39; goes here
 precise:
 # configuration for formatter with id &#39;precise&#39; goes here
handlers:
 h1: #This is an id
 # configuration of handler with id &#39;h1&#39; goes here
 formatter: brief
 h2: #This is another id
 # configuration of handler with id &#39;h2&#39; goes here
 formatter: precise
loggers:
 foo.bar.baz:
 # other configuration for logger &#39;foo.bar.baz&#39;
 handlers: [h1, h2]
</pre></div>
</div>
(Note: YAML used here because it’s a little more readable than the
equivalent Python source form for the dictionary.)
The ids for loggers are the logger names which would be used
programmatically to obtain a reference to those loggers, e.g.
<code class="docutils literal notranslate">foo.bar.baz</code>. The ids for Formatters and Filters can be any string
value (such as <code class="docutils literal notranslate">brief</code>, <code class="docutils literal notranslate">precise</code> above) and they are transient,
in that they are only meaningful for processing the configuration
dictionary and used to determine connections between objects, and are
not persisted anywhere when the configuration call is complete.
The above snippet indicates that logger named <code class="docutils literal notranslate">foo.bar.baz</code> should
have two handlers attached to it, which are described by the handler
ids <code class="docutils literal notranslate">h1</code> and <code class="docutils literal notranslate">h2</code>. The formatter for <code class="docutils literal notranslate">h1</code> is that described by id
<code class="docutils literal notranslate">brief</code>, and the formatter for <code class="docutils literal notranslate">h2</code> is that described by id
<code class="docutils literal notranslate">precise</code>.
</div>
<div class="section" id="user-defined-objects">
<h3>16.7.2.4. User-defined objects<a class="headerlink" href="#user-defined-objects" title="Permalink to this headline">¶</a></h3>
The schema supports user-defined objects for handlers, filters and
formatters. (Loggers do not need to have different types for
different instances, so there is no support in this configuration
schema for user-defined logger classes.)
Objects to be configured are described by dictionaries
which detail their configuration. In some places, the logging system
will be able to infer from the context how an object is to be
instantiated, but when a user-defined object is to be instantiated,
the system will not know how to do this. In order to provide complete
flexibility for user-defined object instantiation, the user needs
to provide a ‘factory’ - a callable which is called with a
configuration dictionary and which returns the instantiated object.
This is signalled by an absolute import path to the factory being
made available under the special key <code class="docutils literal notranslate">'()'</code>. Here’s a concrete
example:
<div class="highlight-yaml notranslate"><div class="highlight"><pre>formatters:
 brief:
 format: &#39;%(message)s&#39;
 default:
 format: &#39;%(asctime)s %(levelname)-8s %(name)-15s %(message)s&#39;
 datefmt: &#39;%Y-%m-%d %H:%M:%S&#39;
 custom:
 (): my.package.customFormatterFactory
 bar: baz
 spam: 99.9
 answer: 42
</pre></div>
</div>
The above YAML snippet defines three formatters. The first, with id
<code class="docutils literal notranslate">brief</code>, is a standard <a class="reference internal" href="logging.html#logging.Formatter" title="logging.Formatter"><code class="xref py py-class docutils literal notranslate">logging.Formatter</code></a> instance with the
specified format string. The second, with id <code class="docutils literal notranslate">default</code>, has a
longer format and also defines the time format explicitly, and will
result in a <a class="reference internal" href="logging.html#logging.Formatter" title="logging.Formatter"><code class="xref py py-class docutils literal notranslate">logging.Formatter</code></a> initialized with those two format
strings. Shown in Python source form, the <code class="docutils literal notranslate">brief</code> and <code class="docutils literal notranslate">default</code>
formatters have configuration sub-dictionaries:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>{
 &#39;format&#39; : &#39;%(message)s&#39;
}
</pre></div>
</div>
and:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>{
 &#39;format&#39; : &#39;%(asctime)s %(levelname)-8s %(name)-15s %(message)s&#39;,
 &#39;datefmt&#39; : &#39;%Y-%m-%d %H:%M:%S&#39;
}
</pre></div>
</div>
respectively, and as these dictionaries do not contain the special key
<code class="docutils literal notranslate">'()'</code>, the instantiation is inferred from the context: as a result,
standard <a class="reference internal" href="logging.html#logging.Formatter" title="logging.Formatter"><code class="xref py py-class docutils literal notranslate">logging.Formatter</code></a> instances are created. The
configuration sub-dictionary for the third formatter, with id
<code class="docutils literal notranslate">custom</code>, is:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>{
 &#39;()&#39; : &#39;my.package.customFormatterFactory&#39;,
 &#39;bar&#39; : &#39;baz&#39;,
 &#39;spam&#39; : 99.9,
 &#39;answer&#39; : 42
}
</pre></div>
</div>
and this contains the special key <code class="docutils literal notranslate">'()'</code>, which means that
user-defined instantiation is wanted. In this case, the specified
factory callable will be used. If it is an actual callable it will be
used directly - otherwise, if you specify a string (as in the example)
the actual callable will be located using normal import mechanisms.
The callable will be called with the remaining items in the
configuration sub-dictionary as keyword arguments. In the above
example, the formatter with id <code class="docutils literal notranslate">custom</code> will be assumed to be
returned by the call:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>my.package.customFormatterFactory(bar=&#39;baz&#39;, spam=99.9, answer=42)
</pre></div>
</div>
The key <code class="docutils literal notranslate">'()'</code> has been used as the special key because it is not a
valid keyword parameter name, and so will not clash with the names of
the keyword arguments used in the call. The <code class="docutils literal notranslate">'()'</code> also serves as a
mnemonic that the corresponding value is a callable.
</div>
<div class="section" id="access-to-external-objects">
<h3>16.7.2.5. Access to external objects<a class="headerlink" href="#access-to-external-objects" title="Permalink to this headline">¶</a></h3>
There are times where a configuration needs to refer to objects
external to the configuration, for example <code class="docutils literal notranslate">sys.stderr</code>. If the
configuration dict is constructed using Python code, this is
straightforward, but a problem arises when the configuration is
provided via a text file (e.g. JSON, YAML). In a text file, there is
no standard way to distinguish <code class="docutils literal notranslate">sys.stderr</code> from the literal string
<code class="docutils literal notranslate">'sys.stderr'</code>. To facilitate this distinction, the configuration
system looks for certain special prefixes in string values and
treat them specially. For example, if the literal string
<code class="docutils literal notranslate">'ext://sys.stderr'</code> is provided as a value in the configuration,
then the <code class="docutils literal notranslate">ext://</code> will be stripped off and the remainder of the
value processed using normal import mechanisms.
The handling of such prefixes is done in a way analogous to protocol
handling: there is a generic mechanism to look for prefixes which
match the regular expression <code class="docutils literal notranslate">^(?P&lt;prefix&gt;[a-z]+)://(?P&lt;suffix&gt;.*)$</code>
whereby, if the <code class="docutils literal notranslate">prefix</code> is recognised, the <code class="docutils literal notranslate">suffix</code> is processed
in a prefix-dependent manner and the result of the processing replaces
the string value. If the prefix is not recognised, then the string
value will be left as-is.
</div>
<div class="section" id="access-to-internal-objects">
<h3>16.7.2.6. Access to internal objects<a class="headerlink" href="#access-to-internal-objects" title="Permalink to this headline">¶</a></h3>
As well as external objects, there is sometimes also a need to refer
to objects in the configuration. This will be done implicitly by the
configuration system for things that it knows about. For example, the
string value <code class="docutils literal notranslate">'DEBUG'</code> for a <code class="docutils literal notranslate">level</code> in a logger or handler will
automatically be converted to the value <code class="docutils literal notranslate">logging.DEBUG</code>, and the
<code class="docutils literal notranslate">handlers</code>, <code class="docutils literal notranslate">filters</code> and <code class="docutils literal notranslate">formatter</code> entries will take an
object id and resolve to the appropriate destination object.
However, a more generic mechanism is needed for user-defined
objects which are not known to the <a class="reference internal" href="logging.html#module-logging" title="logging: Flexible event logging system for applications."><code class="xref py py-mod docutils literal notranslate">logging</code></a> module. For
example, consider <a class="reference internal" href="logging.handlers.html#logging.handlers.MemoryHandler" title="logging.handlers.MemoryHandler"><code class="xref py py-class docutils literal notranslate">logging.handlers.MemoryHandler</code></a>, which takes
a <code class="docutils literal notranslate">target</code> argument which is another handler to delegate to. Since
the system already knows about this class, then in the configuration,
the given <code class="docutils literal notranslate">target</code> just needs to be the object id of the relevant
target handler, and the system will resolve to the handler from the
id. If, however, a user defines a <code class="docutils literal notranslate">my.package.MyHandler</code> which has
an <code class="docutils literal notranslate">alternate</code> handler, the configuration system would not know that
the <code class="docutils literal notranslate">alternate</code> referred to a handler. To cater for this, a generic
resolution system allows the user to specify:
<div class="highlight-yaml notranslate"><div class="highlight"><pre>handlers:
 file:
 # configuration of file handler goes here

custom:
 (): my.package.MyHandler
 alternate: cfg://handlers.file
</pre></div>
</div>
The literal string <code class="docutils literal notranslate">'cfg://handlers.file'</code> will be resolved in an
analogous way to strings with the <code class="docutils literal notranslate">ext://</code> prefix, but looking
in the configuration itself rather than the import namespace. The
mechanism allows access by dot or by index, in a similar way to
that provided by <code class="docutils literal notranslate">str.format</code>. Thus, given the following snippet:
<div class="highlight-yaml notranslate"><div class="highlight"><pre>handlers:
 email:
 class: logging.handlers.SMTPHandler
 mailhost: localhost
 fromaddr: my_app@domain.tld
 toaddrs:
 - support_team@domain.tld
 - dev_team@domain.tld
 subject: Houston, we have a problem.
</pre></div>
</div>
in the configuration, the string <code class="docutils literal notranslate">'cfg://handlers'</code> would resolve to
the dict with key <code class="docutils literal notranslate">handlers</code>, the string <code class="docutils literal notranslate">'cfg://handlers.email</code>
would resolve to the dict with key <code class="docutils literal notranslate">email</code> in the <code class="docutils literal notranslate">handlers</code> dict,
and so on. The string <code class="docutils literal notranslate">'cfg://handlers.email.toaddrs[1]</code> would
resolve to <code class="docutils literal notranslate">'dev_team.domain.tld'</code> and the string
<code class="docutils literal notranslate">'cfg://handlers.email.toaddrs[0]'</code> would resolve to the value
<code class="docutils literal notranslate">'support_team&#64;domain.tld'</code>. The <code class="docutils literal notranslate">subject</code> value could be accessed
using either <code class="docutils literal notranslate">'cfg://handlers.email.subject'</code> or, equivalently,
<code class="docutils literal notranslate">'cfg://handlers.email[subject]'</code>. The latter form only needs to be
used if the key contains spaces or non-alphanumeric characters. If an
index value consists only of decimal digits, access will be attempted
using the corresponding integer value, falling back to the string
value if needed.
Given a string <code class="docutils literal notranslate">cfg://handlers.myhandler.mykey.123</code>, this will
resolve to <code class="docutils literal notranslate">config_dict['handlers']['myhandler']['mykey']['123']</code>.
If the string is specified as <code class="docutils literal notranslate">cfg://handlers.myhandler.mykey[123]</code>,
the system will attempt to retrieve the value from
<code class="docutils literal notranslate">config_dict['handlers']['myhandler']['mykey'][123]</code>, and fall back
to <code class="docutils literal notranslate">config_dict['handlers']['myhandler']['mykey']['123']</code> if that
fails.
</div>
<div class="section" id="import-resolution-and-custom-importers">
<h3>16.7.2.7. Import resolution and custom importers<a class="headerlink" href="#import-resolution-and-custom-importers" title="Permalink to this headline">¶</a></h3>
Import resolution, by default, uses the builtin <a class="reference internal" href="functions.html#__import__" title="__import__"><code class="xref py py-func docutils literal notranslate">__import__()</code></a> function
to do its importing. You may want to replace this with your own importing
mechanism: if so, you can replace the <code class="xref py py-attr docutils literal notranslate">importer</code> attribute of the
<code class="xref py py-class docutils literal notranslate">DictConfigurator</code> or its superclass, the
<code class="xref py py-class docutils literal notranslate">BaseConfigurator</code> class. However, you need to be
careful because of the way functions are accessed from classes via
descriptors. If you are using a Python callable to do your imports, and you
want to define it at class level rather than instance level, you need to wrap
it with <a class="reference internal" href="functions.html#staticmethod" title="staticmethod"><code class="xref py py-func docutils literal notranslate">staticmethod()</code></a>. For example:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>from importlib import import_module
from logging.config import BaseConfigurator

BaseConfigurator.importer = staticmethod(import_module)
</pre></div>
</div>
You don’t need to wrap with <a class="reference internal" href="functions.html#staticmethod" title="staticmethod"><code class="xref py py-func docutils literal notranslate">staticmethod()</code></a> if you’re setting the import
callable on a configurator instance.
</div>
</div>
<div class="section" id="configuration-file-format">
<h2>16.7.3. Configuration file format<a class="headerlink" href="#configuration-file-format" title="Permalink to this headline">¶</a></h2>
The configuration file format understood by <a class="reference internal" href="#logging.config.fileConfig" title="logging.config.fileConfig"><code class="xref py py-func docutils literal notranslate">fileConfig()</code></a> is based on
<a class="reference internal" href="configparser.html#module-configparser" title="configparser: Configuration file parser."><code class="xref py py-mod docutils literal notranslate">configparser</code></a> functionality. The file must contain sections called
<code class="docutils literal notranslate">[loggers]</code>, <code class="docutils literal notranslate">[handlers]</code> and <code class="docutils literal notranslate">[formatters]</code> which identify by name the
entities of each type which are defined in the file. For each such entity, there
is a separate section which identifies how that entity is configured. Thus, for
a logger named <code class="docutils literal notranslate">log01</code> in the <code class="docutils literal notranslate">[loggers]</code> section, the relevant
configuration details are held in a section <code class="docutils literal notranslate">[logger_log01]</code>. Similarly, a
handler called <code class="docutils literal notranslate">hand01</code> in the <code class="docutils literal notranslate">[handlers]</code> section will have its
configuration held in a section called <code class="docutils literal notranslate">[handler_hand01]</code>, while a formatter
called <code class="docutils literal notranslate">form01</code> in the <code class="docutils literal notranslate">[formatters]</code> section will have its configuration
specified in a section called <code class="docutils literal notranslate">[formatter_form01]</code>. The root logger
configuration must be specified in a section called <code class="docutils literal notranslate">[logger_root]</code>.
<div class="admonition note">
Note
The <a class="reference internal" href="#logging.config.fileConfig" title="logging.config.fileConfig"><code class="xref py py-func docutils literal notranslate">fileConfig()</code></a> API is older than the <a class="reference internal" href="#logging.config.dictConfig" title="logging.config.dictConfig"><code class="xref py py-func docutils literal notranslate">dictConfig()</code></a> API and does
not provide functionality to cover certain aspects of logging. For example,
you cannot configure <a class="reference internal" href="logging.html#logging.Filter" title="logging.Filter"><code class="xref py py-class docutils literal notranslate">Filter</code></a> objects, which provide for
filtering of messages beyond simple integer levels, using <a class="reference internal" href="#logging.config.fileConfig" title="logging.config.fileConfig"><code class="xref py py-func docutils literal notranslate">fileConfig()</code></a>.
If you need to have instances of <a class="reference internal" href="logging.html#logging.Filter" title="logging.Filter"><code class="xref py py-class docutils literal notranslate">Filter</code></a> in your logging
configuration, you will need to use <a class="reference internal" href="#logging.config.dictConfig" title="logging.config.dictConfig"><code class="xref py py-func docutils literal notranslate">dictConfig()</code></a>. Note that future
enhancements to configuration functionality will be added to
<a class="reference internal" href="#logging.config.dictConfig" title="logging.config.dictConfig"><code class="xref py py-func docutils literal notranslate">dictConfig()</code></a>, so it’s worth considering transitioning to this newer
API when it’s convenient to do so.
</div>
Examples of these sections in the file are given below.
<div class="highlight-ini notranslate"><div class="highlight"><pre>[loggers]
keys=root,log02,log03,log04,log05,log06,log07

[handlers]
keys=hand01,hand02,hand03,hand04,hand05,hand06,hand07,hand08,hand09

[formatters]
keys=form01,form02,form03,form04,form05,form06,form07,form08,form09
</pre></div>
</div>
The root logger must specify a level and a list of handlers. An example of a
root logger section is given below.
<div class="highlight-ini notranslate"><div class="highlight"><pre>[logger_root]
level=NOTSET
handlers=hand01
</pre></div>
</div>
The <code class="docutils literal notranslate">level</code> entry can be one of <code class="docutils literal notranslate">DEBUG, INFO, WARNING, ERROR, CRITICAL</code> or
<code class="docutils literal notranslate">NOTSET</code>. For the root logger only, <code class="docutils literal notranslate">NOTSET</code> means that all messages will be
logged. Level values are <a class="reference internal" href="functions.html#eval" title="eval"><code class="xref py py-func docutils literal notranslate">eval()</code></a>uated in the context of the <code class="docutils literal notranslate">logging</code>
package’s namespace.
The <code class="docutils literal notranslate">handlers</code> entry is a comma-separated list of handler names, which must
appear in the <code class="docutils literal notranslate">[handlers]</code> section. These names must appear in the
<code class="docutils literal notranslate">[handlers]</code> section and have corresponding sections in the configuration
file.
For loggers other than the root logger, some additional information is required.
This is illustrated by the following example.
<div class="highlight-ini notranslate"><div class="highlight"><pre>[logger_parser]
level=DEBUG
handlers=hand01
propagate=1
qualname=compiler.parser
</pre></div>
</div>
The <code class="docutils literal notranslate">level</code> and <code class="docutils literal notranslate">handlers</code> entries are interpreted as for the root logger,
except that if a non-root logger’s level is specified as <code class="docutils literal notranslate">NOTSET</code>, the system
consults loggers higher up the hierarchy to determine the effective level of the
logger. The <code class="docutils literal notranslate">propagate</code> entry is set to 1 to indicate that messages must
propagate to handlers higher up the logger hierarchy from this logger, or 0 to
indicate that messages are not propagated to handlers up the hierarchy. The
<code class="docutils literal notranslate">qualname</code> entry is the hierarchical channel name of the logger, that is to
say the name used by the application to get the logger.
Sections which specify handler configuration are exemplified by the following.
<div class="highlight-ini notranslate"><div class="highlight"><pre>[handler_hand01]
class=StreamHandler
level=NOTSET
formatter=form01
args=(sys.stdout,)
</pre></div>
</div>
The <code class="docutils literal notranslate">class</code> entry indicates the handler’s class (as determined by <a class="reference internal" href="functions.html#eval" title="eval"><code class="xref py py-func docutils literal notranslate">eval()</code></a>
in the <code class="docutils literal notranslate">logging</code> package’s namespace). The <code class="docutils literal notranslate">level</code> is interpreted as for
loggers, and <code class="docutils literal notranslate">NOTSET</code> is taken to mean ‘log everything’.
The <code class="docutils literal notranslate">formatter</code> entry indicates the key name of the formatter for this
handler. If blank, a default formatter (<code class="docutils literal notranslate">logging._defaultFormatter</code>) is used.
If a name is specified, it must appear in the <code class="docutils literal notranslate">[formatters]</code> section and have
a corresponding section in the configuration file.
The <code class="docutils literal notranslate">args</code> entry, when <a class="reference internal" href="functions.html#eval" title="eval"><code class="xref py py-func docutils literal notranslate">eval()</code></a>uated in the context of the <code class="docutils literal notranslate">logging</code>
package’s namespace, is the list of arguments to the constructor for the handler
class. Refer to the constructors for the relevant handlers, or to the examples
below, to see how typical entries are constructed.
<div class="highlight-ini notranslate"><div class="highlight"><pre>[handler_hand02]
class=FileHandler
level=DEBUG
formatter=form02
args=(&#39;python.log&#39;, &#39;w&#39;)

[handler_hand03]
class=handlers.SocketHandler
level=INFO
formatter=form03
args=(&#39;localhost&#39;, handlers.DEFAULT_TCP_LOGGING_PORT)

[handler_hand04]
class=handlers.DatagramHandler
level=WARN
formatter=form04
args=(&#39;localhost&#39;, handlers.DEFAULT_UDP_LOGGING_PORT)

[handler_hand05]
class=handlers.SysLogHandler
level=ERROR
formatter=form05
args=((&#39;localhost&#39;, handlers.SYSLOG_UDP_PORT), handlers.SysLogHandler.LOG_USER)

[handler_hand06]
class=handlers.NTEventLogHandler
level=CRITICAL
formatter=form06
args=(&#39;Python Application&#39;, &#39;&#39;, &#39;Application&#39;)

[handler_hand07]
class=handlers.SMTPHandler
level=WARN
formatter=form07
args=(&#39;localhost&#39;, &#39;from@abc&#39;, [&#39;user1@abc&#39;, &#39;user2@xyz&#39;], &#39;Logger Subject&#39;)

[handler_hand08]
class=handlers.MemoryHandler
level=NOTSET
formatter=form08
target=
args=(10, ERROR)

[handler_hand09]
class=handlers.HTTPHandler
level=NOTSET
formatter=form09
args=(&#39;localhost:9022&#39;, &#39;/log&#39;, &#39;GET&#39;)
</pre></div>
</div>
Sections which specify formatter configuration are typified by the following.
<div class="highlight-ini notranslate"><div class="highlight"><pre>[formatter_form01]
format=F1 %(asctime)s %(levelname)s %(message)s
datefmt=
class=logging.Formatter
</pre></div>
</div>
The <code class="docutils literal notranslate">format</code> entry is the overall format string, and the <code class="docutils literal notranslate">datefmt</code> entry is
the <code class="xref py py-func docutils literal notranslate">strftime()</code>-compatible date/time format string. If empty, the
package substitutes something which is almost equivalent to specifying the date
format string <code class="docutils literal notranslate">'%Y-%m-%d %H:%M:%S'</code>. This format also specifies milliseconds,
which are appended to the result of using the above format string, with a comma
separator. An example time in this format is <code class="docutils literal notranslate">2003-01-23 00:29:50,411</code>.
The <code class="docutils literal notranslate">class</code> entry is optional. It indicates the name of the formatter’s class
(as a dotted module and class name.) This option is useful for instantiating a
<a class="reference internal" href="logging.html#logging.Formatter" title="logging.Formatter"><code class="xref py py-class docutils literal notranslate">Formatter</code></a> subclass. Subclasses of
<a class="reference internal" href="logging.html#logging.Formatter" title="logging.Formatter"><code class="xref py py-class docutils literal notranslate">Formatter</code></a> can present exception tracebacks in an expanded or
condensed format.
<div class="admonition note">
Note
Due to the use of <a class="reference internal" href="functions.html#eval" title="eval"><code class="xref py py-func docutils literal notranslate">eval()</code></a> as described above, there are
potential security risks which result from using the <a class="reference internal" href="#logging.config.listen" title="logging.config.listen"><code class="xref py py-func docutils literal notranslate">listen()</code></a> to send
and receive configurations via sockets. The risks are limited to where
multiple users with no mutual trust run code on the same machine; see the
<a class="reference internal" href="#logging.config.listen" title="logging.config.listen"><code class="xref py py-func docutils literal notranslate">listen()</code></a> documentation for more information.
</div>
<div class="admonition seealso">
See also
<dl class="last docutils">
<dt>Module <a class="reference internal" href="logging.html#module-logging" title="logging: Flexible event logging system for applications."><code class="xref py py-mod docutils literal notranslate">logging</code></a></dt>
<dd>API reference for the logging module.</dd>
<dt>Module <a class="reference internal" href="logging.handlers.html#module-logging.handlers" title="logging.handlers: Handlers for the logging module."><code class="xref py py-mod docutils literal notranslate">logging.handlers</code></a></dt>
<dd>Useful handlers included with the logging module.</dd>
</dl>
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<li><a class="reference internal" href="#">16.7. <code class="docutils literal notranslate">logging.config</code> — Logging configuration</a><ul>
<li><a class="reference internal" href="#configuration-functions">16.7.1. Configuration functions</a></li>
<li><a class="reference internal" href="#configuration-dictionary-schema">16.7.2. Configuration dictionary schema</a><ul>
<li><a class="reference internal" href="#dictionary-schema-details">16.7.2.1. Dictionary Schema Details</a></li>
<li><a class="reference internal" href="#incremental-configuration">16.7.2.2. Incremental Configuration</a></li>
<li><a class="reference internal" href="#object-connections">16.7.2.3. Object connections</a></li>
<li><a class="reference internal" href="#user-defined-objects">16.7.2.4. User-defined objects</a></li>
<li><a class="reference internal" href="#access-to-external-objects">16.7.2.5. Access to external objects</a></li>
<li><a class="reference internal" href="#access-to-internal-objects">16.7.2.6. Access to internal objects</a></li>
<li><a class="reference internal" href="#import-resolution-and-custom-importers">16.7.2.7. Import resolution and custom importers</a></li>
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<li><a class="reference internal" href="#configuration-file-format">16.7.3. Configuration file format</a></li>
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