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Python Library Reference |  |
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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 match determines the disposition of the match. Each entry is a tuple of the form (action, message, category, module, lineno), where:
| Value | Disposition |
|---|---|
"error" |
turn matching warnings into exceptions |
"ignore" |
never print matching warnings |
"always" |
always print matching warnings |
"default" |
print the first occurrence of matching warnings for each location where the warning is issued |
"module" |
print the first occurrence of matching warnings for each module where the warning is issued |
"once" |
print only the first occurrence of matching warnings, regardless of location |
0 to match all line
numbers
Since the Warning class is derived from the built-in
Exception class, to turn a warning into an error we simply
raise category(message).
The warnings filter is initialized by -W options passed
to the Python interpreter command line. The interpreter saves the
arguments for all -W options without interpretation in
sys.warnoptions; the warnings module parses these when
it is first imported (invalid options are ignored, after printing a
message to sys.stderr).
The warnings that are ignored by default may be enabled by passing -Wd to the interpreter. This enables default handling for all warnings, including those that are normally ignored by default. This is particular useful for enabling ImportWarning when debugging problems importing a developed package. ImportWarning can also be enabled explicitly in Python code using:
warnings.simplefilter('default', ImportWarning)
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Python Library Reference | |
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