yaml.constructor.ConstructorError: could not determine a constructor for the tag 'tag:yaml.org,2002:value'

[aleksandr-vin]

The yaml doc

op: =

is not loading:

(venv) % pip install pyyaml
Collecting pyyaml
  Using cached PyYAML-6.0-cp310-cp310-macosx_11_0_arm64.whl (173 kB)
Installing collected packages: pyyaml
Successfully installed pyyaml-6.0
(venv) % python -c "import yaml ; yaml.load_safe('op: = ')"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
AttributeError: module 'yaml' has no attribute 'load_safe'. Did you mean: 'load_all'?
(venv) % python -c "import yaml ; yaml.safe_load('op: = ')"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/private/tmp/venv/lib/python3.10/site-packages/yaml/__init__.py", line 125, in safe_load
    return load(stream, SafeLoader)
  File "/private/tmp/venv/lib/python3.10/site-packages/yaml/__init__.py", line 81, in load
    return loader.get_single_data()
  File "/private/tmp/venv/lib/python3.10/site-packages/yaml/constructor.py", line 51, in get_single_data
    return self.construct_document(node)
  File "/private/tmp/venv/lib/python3.10/site-packages/yaml/constructor.py", line 60, in construct_document
    for dummy in generator:
  File "/private/tmp/venv/lib/python3.10/site-packages/yaml/constructor.py", line 413, in construct_yaml_map
    value = self.construct_mapping(node)
  File "/private/tmp/venv/lib/python3.10/site-packages/yaml/constructor.py", line 218, in construct_mapping
    return super().construct_mapping(node, deep=deep)
  File "/private/tmp/venv/lib/python3.10/site-packages/yaml/constructor.py", line 143, in construct_mapping
    value = self.construct_object(value_node, deep=deep)
  File "/private/tmp/venv/lib/python3.10/site-packages/yaml/constructor.py", line 100, in construct_object
    data = constructor(self, node)
  File "/private/tmp/venv/lib/python3.10/site-packages/yaml/constructor.py", line 427, in construct_undefined
    raise ConstructorError(None, None,
yaml.constructor.ConstructorError: could not determine a constructor for the tag 'tag:yaml.org,2002:value'
  in "<unicode string>", line 1, column 5:
    op: =
        ^

[aleksandr-vin]

I reported an issue initially on pre-commit/pre-commit-hooks#846 but it looks like its place is here

[nitzmahone]

It looks like you're running afoul of this: https://yaml.org/type/value.html. Short answer is "quote the equals or prefix it with !!str if you want it to work in current PyYAML as a string", since this appears at first blush to be one of those 1.1-side-spec-isms that doesn't have an analogue in 1.2 and PyYAML is mostly 1.1, but someone that's more of a spec expert might correct me if I'm wrong.

[aleksandr-vin]

Thanks @nitzmahone.

I'm getting that yaml part in the process of converting a json data into yaml, with the pipeline like this:

echo '{"op":"="}' | yq -P eval

And the json I receive from Grafana's /api/dashboards/uid/{uid} api call. So it's not easy/tidy to quote or prefix the value.

[perlpunk]

Duplicate of #89

[nitzmahone]

@perlpunk yay for dupe issue necromancy 😆

@aleksandr-vin If you can do things in the Python environment before the document is loaded, the following awful hack will let all subsequent document parses succeed in the presence of a value like that:

del(yaml.resolver.Resolver.yaml_implicit_resolvers['='])

Longer-term, especially since it doesn't look like that type ever really fulfilled its promise, seems like we might want to nuke it.