"dictionary keys changed during iteration" when running checkout_externals

[christophergeiger3]

Summary of Issue:

This was a simple issue but I was stuck on it for a while, so I wanted to share how I fixed it here, in case anyone else faced the same one.

I ran into an error when trying to run checkout_externals for the first time on my local machine, as described here: https://escomp.github.io/CESM/release-cesm2/downloading_cesm.html

git clone -b release-cesm2.1.1 https://github.com/ESCOMP/CESM.git my_cesm_sandbox
cd my_cesm_sandbox
./manage_externals/checkout_externals

Produces:

Processing externals description file : Externals.cfg
Checking status of externals: cam, dictionary keys changed during iteration

It turns out that checkout_externals needs to be run with python 2, which may not be the default on your machine anymore, now that python 2 has passed end-of-life.

I fixed the issue by doing:

python2 ./manage_externals/checkout_externals

[billsacks]

Thank you very much for opening this issue. I'm actually going to go ahead and reopen it, because it does seem to be a true issue.

I have reproduced this issue with python 3.8.1. manage_externals should work with python3, but it seems that there was a behavior change in python 3.8 relative to 3.7 that is causing this problem. I'll dig a bit and try to determine a fix.