add_implicit_resolver does not match quoted strings

import re
import uuid
import yaml

regex = re.compile(r'^UUID\((.+)\)$')
yaml.add_implicit_resolver('!uuid', regex)

def convert_uuid(loader, node):
    value = loader.construct_scalar(node)
    str_value = regex.match(value).group(1)
    return uuid.UUID(str_value)

yaml.add_constructor('!uuid', convert_uuid)

print(yaml.load('''
    config:
        abc: UUID(6a02171e-6482-11e9-ab43-f2189845f1cc)
        def: abc
'''))

# {'config': {'abc': UUID('6a02171e-6482-11e9-ab43-f2189845f1cc'), 'def': 'abc'}}

print(yaml.load('''
    config:
        abc: 'UUID(6a02171e-6482-11e9-ab43-f2189845f1cc)'
        def: abc
'''))

# {'config': {'abc': 'UUID(6a02171e-6482-11e9-ab43-f2189845f1cc)', 'def': 'abc'}}

print(yaml.load('''
    config:
        abc: !uuid 'UUID(6a02171e-6482-11e9-ab43-f2189845f1cc)'
        def: abc
'''))

# {'config': {'abc': UUID(6a02171e-6482-11e9-ab43-f2189845f1cc), 'def': 'abc'}}

Maybe this is something I don’t understand about the YAML spec, but if you explicitly tag the value it works. I initially thought it was #294, but I am using PyYAML 5.3.1 with Python 3.8.6.

[ingydotnet]

# would prefer
someKey: @do_not_inherit someValue

There’s no reason you couldn’t do this now using:

someKey: !do_not_inherit someValue
# or:
someKey: !do_not_inherit [ !tag taggedValue ]

where the function you register to !do_not_inherit modifies the constructed value in some way desired by your framework.

Ruamel is a fork of PyYAML. I just took a quick look and all the resolver and constructor functions I mentioned in the previous comment are available in ruamel too.

[ingydotnet]

As @Thom1729 said

Tag resolution is the process of taking each node with a non-specific tag and assigning it a specific tag.

Tags themselves are annotation strings that can be used by the composition/construction process to configure that process. In reality (in PyYAML) tags are keys to look up functions. The actual functions that transform representation nodes into native structures.

For example: the !!bool tag is a key to look up a python function to create a python bool value.

This is the PyYAML code that implicitly tags plain scalar values matching certain patterns: https://github.com/yaml/pyyaml/blob/master/lib/yaml/resolver.py#L170-L175

to the tag tag:yaml.org,2002:python/bool which is configured here: https://github.com/yaml/pyyaml/blob/master/lib/yaml/constructor.py#L665-L667

To tell the constructor to transform the canonical form of the scalar using this function: https://github.com/yaml/pyyaml/blob/8cdff2c80573b8be8e8ad28929264a913a63aa33/lib/yaml/constructor.py#L233 to make the python boolean native value.

The process of turning a node into a canonical form is not well abstracted or exposed by pyyaml. In this boolean example, it simply calls .lower() on the value and uses that as a local dict key.

---

It is easy to apply multiple functions (tags) to a node’s construction, by wrapping calls in sequences. Using @Thom1729 's example, you can:

- !force-inherit [ !tag2 some string ]

it also makes the order of operations visually clear. And you can obviously do this right now in pyyaml; although we are working on ways to make it even cleaner.

---

On the subject of tag resolution and canonical form, this is usually seen in the context of scalars but you can also do this with collections.

For instance you shouldn’t have to tag !color for:

pink: !color { r: 255, g: 192, b: 203 }
blue: { r: 0, g: 0, b: 255 }

and the normalization should be equally powerful. This should be able to produce the same:

pink: r=255 g=192 b=203
blue: [0, 0, 255]

If a schema dictates that a given node in the graph is required to have the tag !color it should be able to express the normalization from various serialization forms as shown above.

A yaml schema is the entity that defines the tags available to a load operation and how the implicit resolution and canonicalization should work.

A schema should be able to be written as a yaml data file and exposed to a YAML API like pyyaml’s via something like:

native = yaml.load(yaml_input, schema_file='drawing-schema.yaml')

We’re not there yet, but we’re working on it.