Warnings display twice in Jupyter notebooks

Description

Previously I was seeing this behavior in both a Jupyter notebook context and in an interactive python session in a terminal, but pulling the most recent main branch updates and doing a dev install seems to have fixed the latter case. I’m still seeing duplicate warning messages (with minor syntax differences between the two) when I use astropy in a notebook, for example:

WARNING: No observer defined on WCS, SpectralCoord will be converted without any velocity frame change [astropy.wcs.wcsapi.fitswcs]
WARNING:astropy:No observer defined on WCS, SpectralCoord will be converted without any velocity frame change

I imagine this has something to do with the way the AstropyLogger is catching and displaying warnings.warn calls.

Steps to Reproduce

A quick snippet to trigger a warning:

import numpy as np
import astropy.units as u

flux = np.ones(3) * u.Unit("1E-17 erg/s/cm^2/Angstrom")

This displays two warnings:

WARNING: UnitsWarning: '1E-17 erg/s/cm^2/Angstrom' contains multiple slashes, which is discouraged by the FITS standard [astropy.units.format.generic]
WARNING:astropy:UnitsWarning: '1E-17 erg/s/cm^2/Angstrom' contains multiple slashes, which is discouraged by the FITS standard

System Details

Checking that my notebook is actually using the dev version of astropy:

Python 3.8.8 (default, Feb 24 2021, 13:46:16) Numpy 1.20.1 astropy 4.2.dev2287+g8615fc8ca

[rosteen]

p.s. Maybe this is why.

https://github.com/astropy/specutils/blob/57dd2b28e5122e00e28333043192d30ec9f78a9d/specutils/__init__.py#L55-L58

That’s exactly where I had just started my investigation. Thanks for the tips!

[rosteen]

Ah, I just did a pull not fetch. I have astropy 4.3.dev1123+g8615fc8ca after fetching the tags.

Upon further inspection it looks like you’re correct about this originating somewhere other than astropy, I’ll close this issue and investigate further. I suspect it’s actually a specutils issue…