That example is pretty broken anyways.

Colorbars changed to behave more like normal axes, though I thought they changed in 3.1. Can you bisect this and see what commit made this change?

I'm ill-disposed to SymLogNorm, but maybe its an easy fix.

@jklymak good job I'm well-disposed 😉 - I'll try to look into this as I think I have the same issue too!

Bisects to dc51a68

Hmm, well not surprising. I guess the hand-made axes handling that used to be in colorbar did something special with SymLogNorm. This comes back to the issue that @anntzer has that scales and norms are not terribly different. I suspect the correct fix is for someone to gin up a SymLogScale if it doesn't already exist and get that to work and then let it be applied to colorbars. Or special case SymLogNorm in colorbar, but thats a last resort IMHO.

@dstansby, out of curiosity how did you bisect that so fast? When I do a git bisect and rebuild with python -mpip install . it takes quite a while to rebuild mpl each time. Is there an automated way that you've got to make bisecting faster?

You don’t need to pip install each time if you don’t need to rebuild any of the c code. (And you’ve used pip install -e)

Some more tricks (everything here assumes you're in a -e install):

• Even if you need to rebuild c extensions you can just do python setup.py build_ext --inplace which will just rebuild the extensions and skip the rest.
• ccache (https://ccache.dev/) really helps too (because if you're bisecting even only once in a while, you'll be compiling the same files again and again).

So it seems that SymLogNorm itself is also broken, so perhaps not such a bad thing that its colorbar doesn't work: #16376 But of course we should fix these things ASAP.

@greglucas Using pip install -e . is one way to make it faster (as you don't have to actually re-install if only the python changes) and the other is to use ccache so that the c-extensions build almost instantly.

Thanks for the helpful hints on commands! A quick search through the docs doesn't indicate anything telling me about ccache and the wording is pretty vague around the pip install -e . command. I think this would actually be helpful for other new contributors getting started and bisecting, so I will try and look into adding it somewhere in the docs.