In Python, how does one catch warnings as if they were exceptions?
If you just want your script to fail on warnings you can invoke python
with the -W
argument:
python -W error foobar.py
Here's a variation that makes it clearer how to work with only your custom warnings.
import warnings
with warnings.catch_warnings(record=True) as w:
# Cause all warnings to always be triggered.
warnings.simplefilter("always")
# Call some code that triggers a custom warning.
functionThatRaisesWarning()
# ignore any non-custom warnings that may be in the list
w = filter(lambda i: issubclass(i.category, UserWarning), w)
if len(w):
# do something with the first warning
email_admins(w[0].message)
To quote from the python handbook (27.6.4. Testing Warnings):
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)
To handle warnings as errors simply use this:
import warnings
warnings.filterwarnings("error")
After this you will be able to catch warnings same as errors, e.g. this will work:
try:
some_heavy_calculations()
except RuntimeWarning:
breakpoint()
P.S. Added this answer because the best answer in comments contains misspelling: filterwarnigns
instead of filterwarnings
.