Great. FYI, the issue with pyyaml was caused by the "--pre" flag. The reason installing it separately fixes the problem is because it installs it without the "--pre" flag, and then it is already installed when you install the requirements.

I haven't been able to make sense of n-samples and n-iters. Changing the former caused generation to freeze at 0%. Changing the latter seems to generate multiple images, even though the SD docs for n-iters are "sample this often".