Pyyaml does not change `!!` to `tag:yaml.org,2002:` in `add_constructor`
If I try to add a new secondary tag constructor using
add_constructor, then it does not change the constructor tag name
tag:yaml.org,2002:foo. Any tags in the YAML file won't be found, and will cause a runtime error.
I have attached a patch to show how this issue can be resolved, but I would guess that there is a better solution using the parser.