pyYAML Errors on "!" in a string

Question

First, a disclaimer: I'm not too familiar with YAML. I'm trying to parse a YAML doc into Key Value Pairs (don't worry about how I'm doing it. I've got that bit handled) My file used to look something like: ``` world: people: name:Suzy address:chez-bob ``` Then, someone went and changed it. ``` world: people: name:!$uzy address:chez-bob ``` And I get this parse error: ``` yaml.constructor.ConstructorError: could not determine a constructor for the tag '!$uzy' ``` What does this even mean? How would I go about getting it to just interpret !$ as just two characters? I just want a dictionary of string keys and values! Also, editing the yaml files is not an option. Problem must be fixed in the code using the parser.

Accepted Answer

Exclamation mark is a prefix for YAML tags. The parser has to implement a constructor for it by the tag name. There are some default tags like `!!bool`, `!!int`, etc. and even some Python specific tags like `!!python/tuple`.

You can define your own constructors and even constructors for multiple tags caught by a prefix. By defining the prefix to `''`, you can catch all the tags and ignore them. You can return the tag and its value from the constructor to just treat it all as text.

```
>>> import yaml
>>> def default_ctor(loader, tag_suffix, node):
...     print loader
...     print tag_suffix
...     print node
...     return tag_suffix + ' ' + node.value
...
>>> yaml.add_multi_constructor('', default_ctor)
>>> yaml.load(y)
<yaml.loader.Loader object at 0xb76ce8ec>
!$uzy
ScalarNode(tag=u'!$uzy', value=u'')
{'world': {'people': {'name': '!$uzy', 'address': 'chez-bob'}}}
>>>
```

pyYAML Errors on "!" in a string

Solution

Problem