y|Y|n|N not Recognised as Booleans

[dennisconrad]

According to https://yaml.org/type/bool.html, y, Y. n, and N are Boolean scalars.

PyYAML, however, does not recognise them as such, and parses them as strings.

Example:

Python 3.6.5 (default, Dec 11 2018, 12:40:45) 
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.39.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import yaml
>>> yaml.load('yes')
True
>>> yaml.load('y')
'y'
>>> 

[dennisconrad]

PR: #248

[gar1t]

It's really unfortunate that the YAML spec has such an extensive list of values that decode as bool. The single char variants are pretty incredible.

It forces this spelling:

params:
  x: 123
  'y': 456

Without the quotes, the otherwise straight forward spelling of two common parameters has one of those turning up as a boolean.

That's not just idiosyncratic, it's unusable. As a user-facing data-oriented spec I think that's broken.

I was surprised that the PR above had not been merged but after this seeing this problem, I would count PyYAML's treatment of single char spellings of bools as a feature and not a bug. It's unfortunate that the spec goes this far as it presents a nasty trade off between usability and cross system compatibility -- the primary goals of YAML.