warning control "once"

While ignoring warnings works well, I can’t make the warning appear only once (as they actually should do as default behaviour)

I have a (potentially corrupt) fits file that outputs tons of warnings like: WARNING: The following header keyword is invalid or follows an unrecognized non-standard convention: ??????????????????????????????????????????????????????????????????????????????? [astropy.io.fits.card] , even if I explicitly set the warning filter to “once”, they keep coming…

Is this wanted behaviour? If so, why, and can we not change it, or at least allow control over it?

[Laubeee]

Sure thing. The fits is available in our public archive

then just:

from astropy.io import fits
h = fits.getheader("INPE_20120103_113000_58.fit.gz")

and you should see all the warnings.

Then using the linked example about warning control, suppressing it with ignore works, but “once” does the same as “default”…

warnings.filterwarnings('once', category=AstropyUserWarning, append=True)

the python docs state:

default: print the first occurrence of matching warnings for each location (module + line number) where the warning is issued

as far as I can tell all those warnings come from the exact same module+line number so IMO only one warning should be printed with default settings…?

Tested on Win10 with astropy4.0, python 3.7.2

[saimn]

Finally had a more detailed look, and that’s Python’s warnings behavior:

In [1]: import warnings

In [2]: warnings.warn('hello')
<ipython-input-2-bba56b013a54>:1: UserWarning: hello
  warnings.warn('hello')

In [3]: warnings.warn('hello')
<ipython-input-3-bba56b013a54>:1: UserWarning: hello
  warnings.warn('hello')

In [4]: for i in range(5):
   ...:     warnings.warn('hello')
   ...: 
<ipython-input-4-3e5aa4640a88>:2: UserWarning: hello
  warnings.warn('hello')

In [5]: for i in range(5):
   ...:     with warnings.catch_warnings():
   ...:         pass
   ...:     warnings.warn('hello')
   ...: 
<ipython-input-5-4df48fc8ac58>:4: UserWarning: hello
  warnings.warn('hello')
<ipython-input-5-4df48fc8ac58>:4: UserWarning: hello
  warnings.warn('hello')
<ipython-input-5-4df48fc8ac58>:4: UserWarning: hello
  warnings.warn('hello')
<ipython-input-5-4df48fc8ac58>:4: UserWarning: hello
  warnings.warn('hello')
<ipython-input-5-4df48fc8ac58>:4: UserWarning: hello
  warnings.warn('hello')

There is some buffering when calling warnings.warn in a loop, but this is not the case if you call warnings.catch_warnings in the loop iterations. So this is not an Astropy issue, closing this.