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value="dark">Dark</option> </select> </label> <div> <h3><a href="../contents.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate">warnings</code> — Warning control</a><ul> <li><a class="reference internal" href="#warning-categories">Warning Categories</a></li> <li><a class="reference internal" href="#the-warnings-filter">The Warnings Filter</a><ul> <li><a class="reference internal" href="#repeated-warning-suppression-criteria">Repeated Warning Suppression Criteria</a></li> <li><a class="reference internal" href="#describing-warning-filters">Describing Warning Filters</a></li> <li><a class="reference internal" href="#default-warning-filter">Default Warning Filter</a></li> <li><a class="reference internal" href="#overriding-the-default-filter">Overriding the default filter</a></li> </ul> </li> <li><a class="reference internal" href="#temporarily-suppressing-warnings">Temporarily Suppressing Warnings</a></li> <li><a class="reference internal" href="#testing-warnings">Testing Warnings</a></li> <li><a class="reference internal" href="#updating-code-for-new-versions-of-dependencies">Updating Code For New Versions of Dependencies</a></li> <li><a class="reference internal" href="#available-functions">Available Functions</a><ul> <li><a class="reference internal" href="#warnings.warn"><code class="docutils literal notranslate">warn()</code></a></li> <li><a class="reference internal" href="#warnings.warn_explicit"><code class="docutils literal notranslate">warn_explicit()</code></a></li> <li><a class="reference internal" href="#warnings.showwarning"><code class="docutils literal notranslate">showwarning()</code></a></li> <li><a class="reference internal" href="#warnings.formatwarning"><code class="docutils literal notranslate">formatwarning()</code></a></li> <li><a class="reference internal" href="#warnings.filterwarnings"><code class="docutils literal notranslate">filterwarnings()</code></a></li> <li><a class="reference internal" href="#warnings.simplefilter"><code class="docutils literal notranslate">simplefilter()</code></a></li> <li><a class="reference internal" href="#warnings.resetwarnings"><code class="docutils literal notranslate">resetwarnings()</code></a></li> <li><a class="reference internal" href="#warnings.deprecated"><code class="docutils literal notranslate">deprecated()</code></a></li> </ul> </li> <li><a class="reference internal" href="#available-context-managers">Available Context Managers</a><ul> <li><a class="reference internal" href="#warnings.catch_warnings"><code class="docutils literal notranslate">catch_warnings</code></a></li> </ul> </li> </ul> </li> </ul> </div> <div> <h4>Previous topic</h4> <a href="__main__.html" title="previous chapter"><code class="xref py py-mod docutils literal notranslate">__main__</code> — Top-level code environment</a> </div> <div> <h4>Next topic</h4> <a href="dataclasses.html" 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program. For example, one might want to issue a warning when a program uses an obsolete module. Python programmers issue warnings by calling the <a class="reference internal" href="#warnings.warn" title="warnings.warn"><code class="xref py py-func docutils literal notranslate">warn()</code></a> function defined in this module. (C programmers use <a class="reference internal" href="../c-api/exceptions.html#c.PyErr_WarnEx" title="PyErr_WarnEx"><code class="xref c c-func docutils literal notranslate">PyErr_WarnEx()</code></a>; see <a class="reference internal" href="../c-api/exceptions.html#exceptionhandling">Exception Handling</a> for details). Warning messages are normally written to <a class="reference internal" href="sys.html#sys.stderr" title="sys.stderr"><code class="xref py py-data docutils literal notranslate">sys.stderr</code></a>, but their disposition can be changed flexibly, from ignoring all warnings to turning them into exceptions. The disposition of warnings can vary based on the <a class="reference internal" href="#warning-categories">warning category</a>, the text of the warning message, and the source location where it is issued. Repetitions of a particular warning for the same source location are typically suppressed. There are two stages in warning control: first, each time a warning is issued, a determination is made whether a message should be issued or not; next, if a message is to be issued, it is formatted and printed using a user-settable hook. The determination whether to issue a warning message is controlled by the <a class="reference internal" href="#warning-filter">warning filter</a>, which is a sequence of matching rules and actions. Rules can be added to the filter by calling <a class="reference internal" href="#warnings.filterwarnings" title="warnings.filterwarnings"><code class="xref py py-func docutils literal notranslate">filterwarnings()</code></a> and reset to its default state by calling <a class="reference internal" href="#warnings.resetwarnings" title="warnings.resetwarnings"><code class="xref py py-func docutils literal notranslate">resetwarnings()</code></a>. The printing of warning messages is done by calling <a class="reference internal" href="#warnings.showwarning" title="warnings.showwarning"><code class="xref py py-func docutils literal notranslate">showwarning()</code></a>, which may be overridden; the default implementation of this function formats the message by calling <a class="reference internal" href="#warnings.formatwarning" title="warnings.formatwarning"><code class="xref py py-func docutils literal notranslate">formatwarning()</code></a>, which is also available for use by custom implementations. <div class="admonition seealso"> See also <a class="reference internal" href="logging.html#logging.captureWarnings" title="logging.captureWarnings"><code class="xref py py-func docutils literal notranslate">logging.captureWarnings()</code></a> allows you to handle all warnings with the standard logging infrastructure. </div> <section id="warning-categories"> <h2>Warning Categories<a class="headerlink" href="#warning-categories" title="Link to this heading">¶</a></h2> There are a number of built-in exceptions that represent warning categories. This categorization is useful to be able to filter out groups of warnings. While these are technically <a class="reference internal" href="exceptions.html#warning-categories-as-exceptions">built-in exceptions</a>, they are documented here, because conceptually they belong to the warnings mechanism. User code can define additional warning categories by subclassing one of the standard warning categories. A warning category must always be a subclass of the <a class="reference internal" href="exceptions.html#Warning" title="Warning"><code class="xref py py-exc docutils literal notranslate">Warning</code></a> class. The following warnings category classes are currently defined: <table class="docutils align-default"> <thead> <tr class="row-odd"><th class="head">Class</th> <th class="head">Description</th> </tr> </thead> <tbody> <tr class="row-even"><td><a class="reference internal" href="exceptions.html#Warning" title="Warning"><code class="xref py py-exc docutils literal notranslate">Warning</code></a></td> <td>This is the base class of all warning category classes. It is a subclass of <a class="reference internal" href="exceptions.html#Exception" title="Exception"><code class="xref py py-exc docutils literal notranslate">Exception</code></a>.</td> </tr> <tr class="row-odd"><td><a class="reference internal" href="exceptions.html#UserWarning" title="UserWarning"><code class="xref py py-exc docutils literal notranslate">UserWarning</code></a></td> <td>The default category for <a class="reference internal" href="#warnings.warn" title="warnings.warn"><code class="xref py py-func docutils literal notranslate">warn()</code></a>.</td> </tr> <tr class="row-even"><td><a class="reference internal" href="exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-exc docutils literal notranslate">DeprecationWarning</code></a></td> <td>Base category for warnings about deprecated features when those warnings are intended for other Python developers (ignored by default, unless triggered by code in <code class="docutils literal notranslate">__main__</code>).</td> </tr> <tr class="row-odd"><td><a class="reference internal" href="exceptions.html#SyntaxWarning" title="SyntaxWarning"><code class="xref py py-exc docutils literal notranslate">SyntaxWarning</code></a></td> <td>Base category for warnings about dubious syntactic features.</td> </tr> <tr class="row-even"><td><a class="reference internal" href="exceptions.html#RuntimeWarning" title="RuntimeWarning"><code class="xref py py-exc docutils literal notranslate">RuntimeWarning</code></a></td> <td>Base category for warnings about dubious runtime features.</td> </tr> <tr class="row-odd"><td><a class="reference internal" href="exceptions.html#FutureWarning" title="FutureWarning"><code class="xref py py-exc docutils literal notranslate">FutureWarning</code></a></td> <td>Base category for warnings about deprecated features when those warnings are intended for end users of applications that are written in Python.</td> </tr> <tr class="row-even"><td><a class="reference internal" href="exceptions.html#PendingDeprecationWarning" title="PendingDeprecationWarning"><code class="xref py py-exc docutils literal notranslate">PendingDeprecationWarning</code></a></td> <td>Base category for warnings about features that will be deprecated in the future (ignored by default).</td> </tr> <tr class="row-odd"><td><a class="reference internal" href="exceptions.html#ImportWarning" title="ImportWarning"><code class="xref py py-exc docutils literal notranslate">ImportWarning</code></a></td> <td>Base category for warnings triggered during the process of importing a module (ignored by default).</td> </tr> <tr class="row-even"><td><a class="reference internal" href="exceptions.html#UnicodeWarning" title="UnicodeWarning"><code class="xref py py-exc docutils literal notranslate">UnicodeWarning</code></a></td> <td>Base category for warnings related to Unicode.</td> </tr> <tr class="row-odd"><td><a class="reference internal" href="exceptions.html#BytesWarning" title="BytesWarning"><code class="xref py py-exc docutils literal notranslate">BytesWarning</code></a></td> <td>Base category for warnings related to <a class="reference internal" href="stdtypes.html#bytes" title="bytes"><code class="xref py py-class docutils literal notranslate">bytes</code></a> and <a class="reference internal" href="stdtypes.html#bytearray" title="bytearray"><code class="xref py py-class docutils literal notranslate">bytearray</code></a>.</td> </tr> <tr class="row-even"><td><a class="reference internal" href="exceptions.html#ResourceWarning" title="ResourceWarning"><code class="xref py py-exc docutils literal notranslate">ResourceWarning</code></a></td> <td>Base category for warnings related to resource usage (ignored by default).</td> </tr> </tbody> </table> <div class="versionchanged"> Changed in version 3.7: Previously <a class="reference internal" href="exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-exc docutils literal notranslate">DeprecationWarning</code></a> and <a class="reference internal" href="exceptions.html#FutureWarning" title="FutureWarning"><code class="xref py py-exc docutils literal notranslate">FutureWarning</code></a> were distinguished based on whether a feature was being removed entirely or changing its behaviour. They are now distinguished based on their intended audience and the way they’re handled by the default warnings filters. </div> </section> <section id="the-warnings-filter"> <h2>The Warnings Filter<a class="headerlink" href="#the-warnings-filter" title="Link to this heading">¶</a></h2> The warnings filter controls whether warnings are ignored, displayed, or turned into errors (raising an exception). Conceptually, the warnings filter maintains an ordered list of filter specifications; any specific warning is matched against each filter specification in the list in turn until a match is found; the filter determines the disposition of the match. Each entry is a tuple of the form (action, message, category, module, lineno), where: <ul> <li>action is one of the following strings: <table class="docutils align-default"> <thead> <tr class="row-odd"><th class="head">Value</th> <th class="head">Disposition</th> </tr> </thead> <tbody> <tr class="row-even"><td><code class="docutils literal notranslate">"default"</code></td> <td>print the first occurrence of matching warnings for each location (module + line number) where the warning is issued</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">"error"</code></td> <td>turn matching warnings into exceptions</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate">"ignore"</code></td> <td>never print matching warnings</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">"always"</code></td> <td>always print matching warnings</td> </tr> <tr class="row-even"><td><code class="docutils literal notranslate">"module"</code></td> <td>print the first occurrence of matching warnings for each module where the warning is issued (regardless of line number)</td> </tr> <tr class="row-odd"><td><code class="docutils literal notranslate">"once"</code></td> <td>print only the first occurrence of matching warnings, regardless of location</td> </tr> </tbody> </table> </li> <li>message is a string containing a regular expression that the start of the warning message must match, case-insensitively. In <a class="reference internal" href="../using/cmdline.html#cmdoption-W"><code class="xref std std-option docutils literal notranslate">-W</code></a> and <a class="reference internal" href="../using/cmdline.html#envvar-PYTHONWARNINGS"><code class="xref std std-envvar docutils literal notranslate">PYTHONWARNINGS</code></a>, message is a literal string that the start of the warning message must contain (case-insensitively), ignoring any whitespace at the start or end of message.</li> <li>category is a class (a subclass of <a class="reference internal" href="exceptions.html#Warning" title="Warning"><code class="xref py py-exc docutils literal notranslate">Warning</code></a>) of which the warning category must be a subclass in order to match.</li> <li>module is a string containing a regular expression that the start of the fully qualified module name must match, case-sensitively. In <a class="reference internal" href="../using/cmdline.html#cmdoption-W"><code class="xref std std-option docutils literal notranslate">-W</code></a> and <a class="reference internal" href="../using/cmdline.html#envvar-PYTHONWARNINGS"><code class="xref std std-envvar docutils literal notranslate">PYTHONWARNINGS</code></a>, module is a literal string that the fully qualified module name must be equal to (case-sensitively), ignoring any whitespace at the start or end of module.</li> <li>lineno is an integer that the line number where the warning occurred must match, or <code class="docutils literal notranslate">0</code> to match all line numbers.</li> </ul> Since the <a class="reference internal" href="exceptions.html#Warning" title="Warning"><code class="xref py py-exc docutils literal notranslate">Warning</code></a> class is derived from the built-in <a class="reference internal" href="exceptions.html#Exception" title="Exception"><code class="xref py py-exc docutils literal notranslate">Exception</code></a> class, to turn a warning into an error we simply raise <code class="docutils literal notranslate">category(message)</code>. If a warning is reported and doesn’t match any registered filter then the “default” action is applied (hence its name). <section id="repeated-warning-suppression-criteria"> <h3>Repeated Warning Suppression Criteria<a class="headerlink" href="#repeated-warning-suppression-criteria" title="Link to this heading">¶</a></h3> The filters that suppress repeated warnings apply the following criteria to determine if a warning is considered a repeat: <ul class="simple"> <li><code class="docutils literal notranslate">"default"</code>: A warning is considered a repeat only if the (message, category, module, lineno) are all the same.</li> <li><code class="docutils literal notranslate">"module"</code>: A warning is considered a repeat if the (message, category, module) are the same, ignoring the line number.</li> <li><code class="docutils literal notranslate">"once"</code>: A warning is considered a repeat if the (message, category) are the same, ignoring the module and line number.</li> </ul> </section> <section id="describing-warning-filters"> <h3>Describing Warning Filters<a class="headerlink" href="#describing-warning-filters" title="Link to this heading">¶</a></h3> The warnings filter is initialized by <a class="reference internal" href="../using/cmdline.html#cmdoption-W"><code class="xref std std-option docutils literal notranslate">-W</code></a> options passed to the Python interpreter command line and the <a class="reference internal" href="../using/cmdline.html#envvar-PYTHONWARNINGS"><code class="xref std std-envvar docutils literal notranslate">PYTHONWARNINGS</code></a> environment variable. The interpreter saves the arguments for all supplied entries without interpretation in <a class="reference internal" href="sys.html#sys.warnoptions" title="sys.warnoptions"><code class="xref py py-data docutils literal notranslate">sys.warnoptions</code></a>; the <a class="reference internal" href="#module-warnings" title="warnings: Issue warning messages and control their disposition."><code class="xref py py-mod docutils literal notranslate">warnings</code></a> module parses these when it is first imported (invalid options are ignored, after printing a message to <a class="reference internal" href="sys.html#sys.stderr" title="sys.stderr"><code class="xref py py-data docutils literal notranslate">sys.stderr</code></a>). Individual warnings filters are specified as a sequence of fields separated by colons: <div class="highlight-python3 notranslate"><div class="highlight"><pre>action:message:category:module:line </pre></div> </div> The meaning of each of these fields is as described in <a class="reference internal" href="#warning-filter">The Warnings Filter</a>. When listing multiple filters on a single line (as for <a class="reference internal" href="../using/cmdline.html#envvar-PYTHONWARNINGS"><code class="xref std std-envvar docutils literal notranslate">PYTHONWARNINGS</code></a>), the individual filters are separated by commas and the filters listed later take precedence over those listed before them (as they’re applied left-to-right, and the most recently applied filters take precedence over earlier ones). Commonly used warning filters apply to either all warnings, warnings in a particular category, or warnings raised by particular modules or packages. Some examples: <div class="highlight-python3 notranslate"><div class="highlight"><pre>default # Show all warnings (even those ignored by default) ignore # Ignore all warnings error # Convert all warnings to errors error::ResourceWarning # Treat ResourceWarning messages as errors default::DeprecationWarning # Show DeprecationWarning messages ignore,default:::mymodule # Only report warnings triggered by "mymodule" error:::mymodule # Convert warnings to errors in "mymodule" </pre></div> </div> </section> <section id="default-warning-filter"> <h3>Default Warning Filter<a class="headerlink" href="#default-warning-filter" title="Link to this heading">¶</a></h3> By default, Python installs several warning filters, which can be overridden by the <a class="reference internal" href="../using/cmdline.html#cmdoption-W"><code class="xref std std-option docutils literal notranslate">-W</code></a> command-line option, the <a class="reference internal" href="../using/cmdline.html#envvar-PYTHONWARNINGS"><code class="xref std std-envvar docutils literal notranslate">PYTHONWARNINGS</code></a> environment variable and calls to <a class="reference internal" href="#warnings.filterwarnings" title="warnings.filterwarnings"><code class="xref py py-func docutils literal notranslate">filterwarnings()</code></a>. In regular release builds, the default warning filter has the following entries (in order of precedence): <div class="highlight-python3 notranslate"><div class="highlight"><pre>default::DeprecationWarning:__main__ ignore::DeprecationWarning ignore::PendingDeprecationWarning ignore::ImportWarning ignore::ResourceWarning </pre></div> </div> In a <a class="reference internal" href="../using/configure.html#debug-build">debug build</a>, the list of default warning filters is empty. <div class="versionchanged"> Changed in version 3.2: <a class="reference internal" href="exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-exc docutils literal notranslate">DeprecationWarning</code></a> is now ignored by default in addition to <a class="reference internal" href="exceptions.html#PendingDeprecationWarning" title="PendingDeprecationWarning"><code class="xref py py-exc docutils literal notranslate">PendingDeprecationWarning</code></a>. </div> <div class="versionchanged"> Changed in version 3.7: <a class="reference internal" href="exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-exc docutils literal notranslate">DeprecationWarning</code></a> is once again shown by default when triggered directly by code in <code class="docutils literal notranslate">__main__</code>. </div> <div class="versionchanged"> Changed in version 3.7: <a class="reference internal" href="exceptions.html#BytesWarning" title="BytesWarning"><code class="xref py py-exc docutils literal notranslate">BytesWarning</code></a> no longer appears in the default filter list and is instead configured via <a class="reference internal" href="sys.html#sys.warnoptions" title="sys.warnoptions"><code class="xref py py-data docutils literal notranslate">sys.warnoptions</code></a> when <a class="reference internal" href="../using/cmdline.html#cmdoption-b"><code class="xref std std-option docutils literal notranslate">-b</code></a> is specified twice. </div> </section> <section id="overriding-the-default-filter"> <h3>Overriding the default filter<a class="headerlink" href="#overriding-the-default-filter" title="Link to this heading">¶</a></h3> Developers of applications written in Python may wish to hide all Python level warnings from their users by default, and only display them when running tests or otherwise working on the application. The <a class="reference internal" href="sys.html#sys.warnoptions" title="sys.warnoptions"><code class="xref py py-data docutils literal notranslate">sys.warnoptions</code></a> attribute used to pass filter configurations to the interpreter can be used as a marker to indicate whether or not warnings should be disabled: <div class="highlight-python3 notranslate"><div class="highlight"><pre>import sys if not sys.warnoptions: import warnings warnings.simplefilter("ignore") </pre></div> </div> Developers of test runners for Python code are advised to instead ensure that all warnings are displayed by default for the code under test, using code like: <div class="highlight-python3 notranslate"><div class="highlight"><pre>import sys if not sys.warnoptions: import os, warnings warnings.simplefilter("default") # Change the filter in this process os.environ["PYTHONWARNINGS"] = "default" # Also affect subprocesses </pre></div> </div> Finally, developers of interactive shells that run user code in a namespace other than <code class="docutils literal notranslate">__main__</code> are advised to ensure that <a class="reference internal" href="exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-exc docutils literal notranslate">DeprecationWarning</code></a> messages are made visible by default, using code like the following (where <code class="docutils literal notranslate">user_ns</code> is the module used to execute code entered interactively): <div class="highlight-python3 notranslate"><div class="highlight"><pre>import warnings warnings.filterwarnings("default", category=DeprecationWarning, module=user_ns.get("__name__")) </pre></div> </div> </section> </section> <section id="temporarily-suppressing-warnings"> <h2>Temporarily Suppressing Warnings<a class="headerlink" href="#temporarily-suppressing-warnings" title="Link to this heading">¶</a></h2> If you are using code that you know will raise a warning, such as a deprecated function, but do not want to see the warning (even when warnings have been explicitly configured via the command line), then it is possible to suppress the warning using the <a class="reference internal" href="#warnings.catch_warnings" title="warnings.catch_warnings"><code class="xref py py-class docutils literal notranslate">catch_warnings</code></a> context manager: <div class="highlight-python3 notranslate"><div class="highlight"><pre>import warnings def fxn(): warnings.warn("deprecated", DeprecationWarning) with warnings.catch_warnings(): warnings.simplefilter("ignore") fxn() </pre></div> </div> While within the context manager all warnings will simply be ignored. This allows you to use known-deprecated code without having to see the warning while not suppressing the warning for other code that might not be aware of its use of deprecated code. Note: this can only be guaranteed in a single-threaded application. If two or more threads use the <a class="reference internal" href="#warnings.catch_warnings" title="warnings.catch_warnings"><code class="xref py py-class docutils literal notranslate">catch_warnings</code></a> context manager at the same time, the behavior is undefined. </section> <section id="testing-warnings"> <h2>Testing Warnings<a class="headerlink" href="#testing-warnings" title="Link to this heading">¶</a></h2> To test warnings raised by code, use the <a class="reference internal" href="#warnings.catch_warnings" title="warnings.catch_warnings"><code class="xref py py-class docutils literal notranslate">catch_warnings</code></a> context manager. With it you can temporarily mutate the warnings filter to facilitate your testing. For instance, do the following to capture all raised warnings to check: <div class="highlight-python3 notranslate"><div class="highlight"><pre>import warnings def fxn(): warnings.warn("deprecated", DeprecationWarning) with warnings.catch_warnings(record=True) as w: # Cause all warnings to always be triggered. warnings.simplefilter("always") # Trigger a warning. fxn() # Verify some things assert len(w) == 1 assert issubclass(w[-1].category, DeprecationWarning) assert "deprecated" in str(w[-1].message) </pre></div> </div> One can also cause all warnings to be exceptions by using <code class="docutils literal notranslate">error</code> instead of <code class="docutils literal notranslate">always</code>. One thing to be aware of is that if a warning has already been raised because of a <code class="docutils literal notranslate">once</code>/<code class="docutils literal notranslate">default</code> rule, then no matter what filters are set the warning will not be seen again unless the warnings registry related to the warning has been cleared. Once the context manager exits, the warnings filter is restored to its state when the context was entered. This prevents tests from changing the warnings filter in unexpected ways between tests and leading to indeterminate test results. The <a class="reference internal" href="#warnings.showwarning" title="warnings.showwarning"><code class="xref py py-func docutils literal notranslate">showwarning()</code></a> function in the module is also restored to its original value. Note: this can only be guaranteed in a single-threaded application. If two or more threads use the <a class="reference internal" href="#warnings.catch_warnings" title="warnings.catch_warnings"><code class="xref py py-class docutils literal notranslate">catch_warnings</code></a> context manager at the same time, the behavior is undefined. When testing multiple operations that raise the same kind of warning, it is important to test them in a manner that confirms each operation is raising a new warning (e.g. set warnings to be raised as exceptions and check the operations raise exceptions, check that the length of the warning list continues to increase after each operation, or else delete the previous entries from the warnings list before each new operation). </section> <section id="updating-code-for-new-versions-of-dependencies"> <h2>Updating Code For New Versions of Dependencies<a class="headerlink" href="#updating-code-for-new-versions-of-dependencies" title="Link to this heading">¶</a></h2> Warning categories that are primarily of interest to Python developers (rather than end users of applications written in Python) are ignored by default. Notably, this “ignored by default” list includes <a class="reference internal" href="exceptions.html#DeprecationWarning" title="DeprecationWarning"><code class="xref py py-exc docutils literal notranslate">DeprecationWarning</code></a> (for every module except <code class="docutils literal notranslate">__main__</code>), which means developers should make sure to test their code with typically ignored warnings made visible in order to receive timely notifications of future breaking API changes (whether in the standard library or third party packages). In the ideal case, the code will have a suitable test suite, and the test runner will take care of implicitly enabling all warnings when running tests (the test runner provided by the <a class="reference internal" href="unittest.html#module-unittest" title="unittest: Unit testing framework for Python."><code class="xref py py-mod docutils literal notranslate">unittest</code></a> module does this). In less ideal cases, applications can be checked for use of deprecated interfaces by passing <a class="reference internal" href="../using/cmdline.html#cmdoption-W"><code class="xref std std-option docutils literal notranslate">-Wd</code></a> to the Python interpreter (this is shorthand for <code class="xref std std-option docutils literal notranslate">-W default</code>) or setting <code class="docutils literal notranslate">PYTHONWARNINGS=default</code> in the environment. This enables default handling for all warnings, including those that are ignored by default. To change what action is taken for encountered warnings you can change what argument is passed to <a class="reference internal" href="../using/cmdline.html#cmdoption-W"><code class="xref std std-option docutils literal notranslate">-W</code></a> (e.g. <code class="xref std std-option docutils literal notranslate">-W error</code>). See the <a class="reference internal" href="../using/cmdline.html#cmdoption-W"><code class="xref std std-option docutils literal notranslate">-W</code></a> flag for more details on what is possible. </section> <section id="available-functions"> <h2>Available Functions<a class="headerlink" href="#available-functions" title="Link to this heading">¶</a></h2> <dl class="py function"> <dt class="sig sig-object py" id="warnings.warn"> warnings.warn(message, category=None, stacklevel=1, source=None, *, skip_file_prefixes=())<a class="headerlink" href="#warnings.warn" title="Link to this definition">¶</a></dt> <dd>Issue a warning, or maybe ignore it or raise an exception. The category argument, if given, must be a <a class="reference internal" href="#warning-categories">warning category class</a>; it defaults to <a class="reference internal" href="exceptions.html#UserWarning" title="UserWarning"><code class="xref py py-exc docutils literal notranslate">UserWarning</code></a>. Alternatively, message can be a <a class="reference internal" href="exceptions.html#Warning" title="Warning"><code class="xref py py-exc docutils literal notranslate">Warning</code></a> instance, in which case category will be ignored and <code class="docutils literal notranslate">message.__class__</code> will be used. In this case, the message text will be <code class="docutils literal notranslate">str(message)</code>. This function raises an exception if the particular warning issued is changed into an error by the <a class="reference internal" href="#warning-filter">warnings filter</a>. The stacklevel argument can be used by wrapper functions written in Python, like this: <div class="highlight-python3 notranslate"><div class="highlight"><pre>def deprecated_api(message): warnings.warn(message, DeprecationWarning, stacklevel=2) </pre></div> </div> This makes the warning refer to <code class="docutils literal notranslate">deprecated_api</code>’s caller, rather than to the source of <code class="docutils literal notranslate">deprecated_api</code> itself (since the latter would defeat the purpose of the warning message). The skip_file_prefixes keyword argument can be used to indicate which stack frames are ignored when counting stack levels. This can be useful when you want the warning to always appear at call sites outside of a package when a constant stacklevel does not fit all call paths or is otherwise challenging to maintain. If supplied, it must be a tuple of strings. When prefixes are supplied, stacklevel is implicitly overridden to be <code class="docutils literal notranslate">max(2, stacklevel)</code>. To cause a warning to be attributed to the caller from outside of the current package you might write: <div class="highlight-python3 notranslate"><div class="highlight"><pre># example/lower.py _warn_skips = (os.path.dirname(__file__),) def one_way(r_luxury_yacht=None, t_wobbler_mangrove=None): if r_luxury_yacht: warnings.warn("Please migrate to t_wobbler_mangrove=.", skip_file_prefixes=_warn_skips) # example/higher.py from . import lower def another_way(**kw): lower.one_way(**kw) </pre></div> </div> This makes the warning refer to both the <code class="docutils literal notranslate">example.lower.one_way()</code> and <code class="docutils literal notranslate">package.higher.another_way()</code> call sites only from calling code living outside of <code class="docutils literal notranslate">example</code> package. source, if supplied, is the destroyed object which emitted a <a class="reference internal" href="exceptions.html#ResourceWarning" title="ResourceWarning"><code class="xref py py-exc docutils literal notranslate">ResourceWarning</code></a>. <div class="versionchanged"> Changed in version 3.6: Added source parameter. </div> <div class="versionchanged"> Changed in version 3.12: Added skip_file_prefixes. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="warnings.warn_explicit"> warnings.warn_explicit(message, category, filename, lineno, module=None, registry=None, module_globals=None, source=None)<a class="headerlink" href="#warnings.warn_explicit" title="Link to this definition">¶</a></dt> <dd>This is a low-level interface to the functionality of <a class="reference internal" href="#warnings.warn" title="warnings.warn"><code class="xref py py-func docutils literal notranslate">warn()</code></a>, passing in explicitly the message, category, filename and line number, and optionally the module name and the registry (which should be the <code class="docutils literal notranslate">__warningregistry__</code> dictionary of the module). The module name defaults to the filename with <code class="docutils literal notranslate">.py</code> stripped; if no registry is passed, the warning is never suppressed. message must be a string and category a subclass of <a class="reference internal" href="exceptions.html#Warning" title="Warning"><code class="xref py py-exc docutils literal notranslate">Warning</code></a> or message may be a <a class="reference internal" href="exceptions.html#Warning" title="Warning"><code class="xref py py-exc docutils literal notranslate">Warning</code></a> instance, in which case category will be ignored. module_globals, if supplied, should be the global namespace in use by the code for which the warning is issued. (This argument is used to support displaying source for modules found in zipfiles or other non-filesystem import sources). source, if supplied, is the destroyed object which emitted a <a class="reference internal" href="exceptions.html#ResourceWarning" title="ResourceWarning"><code class="xref py py-exc docutils literal notranslate">ResourceWarning</code></a>. <div class="versionchanged"> Changed in version 3.6: Add the source parameter. </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="warnings.showwarning"> warnings.showwarning(message, category, filename, lineno, file=None, line=None)<a class="headerlink" href="#warnings.showwarning" title="Link to this definition">¶</a></dt> <dd>Write a warning to a file. The default implementation calls <code class="docutils literal notranslate">formatwarning(message, category, filename, lineno, line)</code> and writes the resulting string to file, which defaults to <a class="reference internal" href="sys.html#sys.stderr" title="sys.stderr"><code class="xref py py-data docutils literal notranslate">sys.stderr</code></a>. You may replace this function with any callable by assigning to <code class="docutils literal notranslate">warnings.showwarning</code>. line is a line of source code to be included in the warning message; if line is not supplied, <a class="reference internal" href="#warnings.showwarning" title="warnings.showwarning"><code class="xref py py-func docutils literal notranslate">showwarning()</code></a> will try to read the line specified by filename and lineno. </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="warnings.formatwarning"> warnings.formatwarning(message, category, filename, lineno, line=None)<a class="headerlink" href="#warnings.formatwarning" title="Link to this definition">¶</a></dt> <dd>Format a warning the standard way. This returns a string which may contain embedded newlines and ends in a newline. line is a line of source code to be included in the warning message; if line is not supplied, <a class="reference internal" href="#warnings.formatwarning" title="warnings.formatwarning"><code class="xref py py-func docutils literal notranslate">formatwarning()</code></a> will try to read the line specified by filename and lineno. </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="warnings.filterwarnings"> warnings.filterwarnings(action, message='', category=Warning, module='', lineno=0, append=False)<a class="headerlink" href="#warnings.filterwarnings" title="Link to this definition">¶</a></dt> <dd>Insert an entry into the list of <a class="reference internal" href="#warning-filter">warnings filter specifications</a>. The entry is inserted at the front by default; if append is true, it is inserted at the end. This checks the types of the arguments, compiles the message and module regular expressions, and inserts them as a tuple in the list of warnings filters. Entries closer to the front of the list override entries later in the list, if both match a particular warning. Omitted arguments default to a value that matches everything. </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="warnings.simplefilter"> warnings.simplefilter(action, category=Warning, lineno=0, append=False)<a class="headerlink" href="#warnings.simplefilter" title="Link to this definition">¶</a></dt> <dd>Insert a simple entry into the list of <a class="reference internal" href="#warning-filter">warnings filter specifications</a>. The meaning of the function parameters is as for <a class="reference internal" href="#warnings.filterwarnings" title="warnings.filterwarnings"><code class="xref py py-func docutils literal notranslate">filterwarnings()</code></a>, but regular expressions are not needed as the filter inserted always matches any message in any module as long as the category and line number match. </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="warnings.resetwarnings"> warnings.resetwarnings()<a class="headerlink" href="#warnings.resetwarnings" title="Link to this definition">¶</a></dt> <dd>Reset the warnings filter. This discards the effect of all previous calls to <a class="reference internal" href="#warnings.filterwarnings" title="warnings.filterwarnings"><code class="xref py py-func docutils literal notranslate">filterwarnings()</code></a>, including that of the <a class="reference internal" href="../using/cmdline.html#cmdoption-W"><code class="xref std std-option docutils literal notranslate">-W</code></a> command line options and calls to <a class="reference internal" href="#warnings.simplefilter" title="warnings.simplefilter"><code class="xref py py-func docutils literal notranslate">simplefilter()</code></a>. </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="warnings.deprecated"> @warnings.deprecated(msg, *, category=DeprecationWarning, stacklevel=1)<a class="headerlink" href="#warnings.deprecated" title="Link to this definition">¶</a></dt> <dd>Decorator to indicate that a class, function or overload is deprecated. When this decorator is applied to an object, deprecation warnings may be emitted at runtime when the object is used. <a class="reference internal" href="../glossary.html#term-static-type-checker">static type checkers</a> will also generate a diagnostic on usage of the deprecated object. Usage: <div class="highlight-python3 notranslate"><div class="highlight"><pre>from warnings import deprecated from typing import overload @deprecated("Use B instead") class A: pass @deprecated("Use g instead") def f(): pass @overload @deprecated("int support is deprecated") def g(x: int) -> int: ... @overload def g(x: str) -> int: ... </pre></div> </div> The warning specified by category will be emitted at runtime on use of deprecated objects. For functions, that happens on calls; for classes, on instantiation and on creation of subclasses. If the category is <code class="docutils literal notranslate">None</code>, no warning is emitted at runtime. The stacklevel determines where the warning is emitted. If it is <code class="docutils literal notranslate">1</code> (the default), the warning is emitted at the direct caller of the deprecated object; if it is higher, it is emitted further up the stack. Static type checker behavior is not affected by the category and stacklevel arguments. The deprecation message passed to the decorator is saved in the <code class="docutils literal notranslate">__deprecated__</code> attribute on the decorated object. If applied to an overload, the decorator must be after the <a class="reference internal" href="typing.html#typing.overload" title="typing.overload"><code class="xref py py-func docutils literal notranslate">@overload</code></a> decorator for the attribute to exist on the overload as returned by <a class="reference internal" href="typing.html#typing.get_overloads" title="typing.get_overloads"><code class="xref py py-func docutils literal notranslate">typing.get_overloads()</code></a>. <div class="versionadded"> Added in version 3.13: See <a class="pep reference external" href="https://peps.python.org/pep-0702/">PEP 702</a>. </div> </dd></dl> </section> <section id="available-context-managers"> <h2>Available Context Managers<a class="headerlink" href="#available-context-managers" title="Link to this heading">¶</a></h2> <dl class="py class"> <dt class="sig sig-object py" id="warnings.catch_warnings"> class warnings.catch_warnings(*, record=False, module=None, action=None, category=Warning, lineno=0, append=False)<a class="headerlink" href="#warnings.catch_warnings" title="Link to this definition">¶</a></dt> <dd>A context manager that copies and, upon exit, restores the warnings filter and the <a class="reference internal" href="#warnings.showwarning" title="warnings.showwarning"><code class="xref py py-func docutils literal notranslate">showwarning()</code></a> function. If the record argument is <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-const docutils literal notranslate">False</code></a> (the default) the context manager returns <a class="reference internal" href="constants.html#None" title="None"><code class="xref py py-class docutils literal notranslate">None</code></a> on entry. If record is <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-const docutils literal notranslate">True</code></a>, a list is returned that is progressively populated with objects as seen by a custom <a class="reference internal" href="#warnings.showwarning" title="warnings.showwarning"><code class="xref py py-func docutils literal notranslate">showwarning()</code></a> function (which also suppresses output to <code class="docutils literal notranslate">sys.stdout</code>). Each object in the list has attributes with the same names as the arguments to <a class="reference internal" href="#warnings.showwarning" title="warnings.showwarning"><code class="xref py py-func docutils literal notranslate">showwarning()</code></a>. The module argument takes a module that will be used instead of the module returned when you import <a class="reference internal" href="#module-warnings" title="warnings: Issue warning messages and control their disposition."><code class="xref py py-mod docutils literal notranslate">warnings</code></a> whose filter will be protected. This argument exists primarily for testing the <a class="reference internal" href="#module-warnings" title="warnings: Issue warning messages and control their disposition."><code class="xref py py-mod docutils literal notranslate">warnings</code></a> module itself. If the action argument is not <code class="docutils literal notranslate">None</code>, the remaining arguments are passed to <a class="reference internal" href="#warnings.simplefilter" title="warnings.simplefilter"><code class="xref py py-func docutils literal notranslate">simplefilter()</code></a> as if it were called immediately on entering the context. See <a class="reference internal" href="#warning-filter">The Warnings Filter</a> for the meaning of the category and lineno parameters. <div class="admonition note"> Note The <a class="reference internal" href="#warnings.catch_warnings" title="warnings.catch_warnings"><code class="xref py py-class docutils literal notranslate">catch_warnings</code></a> manager works by replacing and then later restoring the module’s <a class="reference internal" href="#warnings.showwarning" title="warnings.showwarning"><code class="xref py py-func docutils literal notranslate">showwarning()</code></a> function and internal list of filter specifications. This means the context manager is modifying global state and therefore is not thread-safe. </div> <div class="versionchanged"> Changed in version 3.11: Added the action, category, lineno, and append parameters. </div> </dd></dl> </section> </section> <div class="clearer"></div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="Main"> <div class="sphinxsidebarwrapper"> <div> <h3><a href="../contents.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate">warnings</code> — Warning control</a><ul> <li><a class="reference internal" href="#warning-categories">Warning Categories</a></li> <li><a class="reference internal" href="#the-warnings-filter">The Warnings Filter</a><ul> <li><a class="reference internal" href="#repeated-warning-suppression-criteria">Repeated Warning Suppression Criteria</a></li> <li><a class="reference internal" href="#describing-warning-filters">Describing Warning Filters</a></li> <li><a class="reference internal" href="#default-warning-filter">Default Warning Filter</a></li> <li><a class="reference internal" href="#overriding-the-default-filter">Overriding the default filter</a></li> </ul> </li> <li><a class="reference internal" href="#temporarily-suppressing-warnings">Temporarily Suppressing Warnings</a></li> <li><a class="reference internal" href="#testing-warnings">Testing Warnings</a></li> <li><a class="reference internal" href="#updating-code-for-new-versions-of-dependencies">Updating Code For New Versions of Dependencies</a></li> <li><a class="reference internal" href="#available-functions">Available Functions</a><ul> <li><a class="reference internal" href="#warnings.warn"><code class="docutils literal notranslate">warn()</code></a></li> <li><a class="reference internal" href="#warnings.warn_explicit"><code class="docutils literal notranslate">warn_explicit()</code></a></li> <li><a class="reference internal" href="#warnings.showwarning"><code class="docutils literal notranslate">showwarning()</code></a></li> <li><a class="reference internal" href="#warnings.formatwarning"><code class="docutils literal notranslate">formatwarning()</code></a></li> <li><a class="reference internal" href="#warnings.filterwarnings"><code class="docutils literal notranslate">filterwarnings()</code></a></li> <li><a class="reference internal" href="#warnings.simplefilter"><code class="docutils literal notranslate">simplefilter()</code></a></li> <li><a class="reference internal" href="#warnings.resetwarnings"><code class="docutils literal notranslate">resetwarnings()</code></a></li> <li><a class="reference internal" href="#warnings.deprecated"><code class="docutils literal notranslate">deprecated()</code></a></li> </ul> </li> <li><a class="reference internal" href="#available-context-managers">Available Context Managers</a><ul> <li><a class="reference internal" href="#warnings.catch_warnings"><code class="docutils literal notranslate">catch_warnings</code></a></li> </ul> </li> </ul> </li> </ul> </div> <div> <h4>Previous topic</h4> <a href="__main__.html" title="previous chapter"><code class="xref py py-mod docutils literal notranslate">__main__</code> — Top-level code environment</a> </div> <div> <h4>Next topic</h4> <a href="dataclasses.html" title="next chapter"><code class="xref py py-mod docutils literal notranslate">dataclasses</code> — Data Classes</a> </div> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/main/Doc/library/warnings.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </div> <div id="sidebarbutton" title="Collapse sidebar"> « </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="Related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="dataclasses.html" title="dataclasses — Data Classes" >next</a> |</li> <li class="right" > <a href="__main__.html" title="__main__ — Top-level code environment" >previous</a> |</li> <li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; 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