Python warnings system

Astropy uses the Python warnings module to issue warning messages. The details of using the warnings module are general to Python, and apply to any Python software that uses this system. The user can suppress the warnings using the python command line argument -W"ignore" when starting an interactive python session. For example:

$ python -W"ignore"

The user may also use the command line argument when running a python script as follows:

$ python -W"ignore" myscript.py

It is also possible to suppress warnings from within a python script. For instance, the warnings issued from a single call to the astropy.io.fits.writeto function may be suppressed from within a Python script using the warnings.filterwarnings function as follows:

>>> import warnings
>>> from astropy.io import fits
>>> warnings.filterwarnings('ignore', category=UserWarning, append=True)
>>> fits.writeto(filename, data, clobber=True)

An equivalent way to insert an entry into the list of warning filter specifications for simple call warnings.simplefilter:

>>> warnings.simplefilter('ignore', UserWarning)

Astropy includes its own warning class, AstropyUserWarning, on which all warnings from Astropy are based. So one can also ignore warnings from Astropy (while still allowing through warnings from other libraries like Numpy) by using something like:

>>> from astropy.utils.exceptions import AstropyUserWarning
>>> warnings.simplefilter('ignore', category=AstropyUserWarning)

However, warning filters may also be modified just within a certain context using the warnings.catch_warnings context manager:

>>> with warnings.catch_warnings():
...     warnings.simplefilter('ignore', AstropyUserWarning)
...     fits.writeto(filename, data, clobber=True)

Astropy also issues warnings when deprecated API features are used. If you wish to squelch deprecation warnings, you can start Python with -Wi::Deprecation. This sets all deprecation warnings to ignored. There is also an Astropy-specific AstropyDeprecationWarning which can be used to disable deprecation warnings from Astropy only.

See the CPython documentation for more information on the -W argument.