# warnings --- Warning control — Available Functions

> Issue a warning, or maybe ignore it or raise an exception. The category argument, if given, must be a warning category class ; it defaults to UserWarning. Alternatively, message can be a Warning instance, in which case category will be ignored and message.class will be used. In this case, the messag

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## Knowledge

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Issue a warning, or maybe ignore it or raise an exception. The category argument, if given, must be a warning category class ; it defaults to UserWarning. Alternatively, message can be a Warning instance, in which case category will be ignored and message.class will be used. In this case, the message text will be str(message). This function raises an exception if the particular warning issued is changed into an error by the warnings filter . The stacklevel argument can be used by wrapper functions written in Python, like this

This makes the warning refer to deprecated_api's caller, rather than to the source of deprecated_api 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 max(2, stacklevel). To cause a warning to be attributed to the caller from outside of the current package you might write

This makes the warning refer to both the example.lower.one_way() and example.higher.another_way() call sites only from calling code living outside of example package.

source, if supplied, is the destroyed object which emitted a ResourceWarning.

This is a low-level interface to the functionality of warn, passing in explicitly the message, category, filename and line number, and optionally other arguments. message must be a string and category a subclass of Warning or message may be a Warning instance, in which case category will be ignored.

module, if supplied, should be the module name. If no module is passed, the module regular expression in warnings filter will be tested against the module names constructed from the path components starting from all parent directories (with /init.py, .py and, on Windows, .pyw stripped) and against the filename with .py stripped. For example, when the filename is '/path/to/package/module.py', it will be tested against 'path.to.package.module', 'to.package.module' 'package.module', 'module', and '/path/to/package/module'. …

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