all Python 3Exceptionsexception

UserWarning

built-in exceptions

The default category for warnings.warn().

Syntax

raise UserWarning

A common trap: warnings.warn('...') raises nothing — the text goes to stderr and execution continues, so an except UserWarning around the call catches nothing. To make warnings behave like real exceptions you need a filter: warnings.simplefilter('error') or running python -W error. Also, by default a warning from a given source line is printed only the first time it fires, so inside a loop it is easy to miss.

Examples

try:
    raise UserWarning
except UserWarning as e:
    print(type(e).__name__)   # → UserWarning

See also

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