Error on load if YAML key has no value (instead of None)?

Question

I have a YAML file with an unknown number of "layers", so when I load it to a Python dictionary it becomes a nested dictionary.

I don't want to allow keys without values in the YAML file. I'd like to either:

• cause errors during yaml.load() if there are missing values, or
• identify all None values within the resulting nested dictionary.

 

import yaml
with open(input_path, "r") as yaml_file:
    my_dict = yaml.load(yaml_file)

Answer 1

You can redefine the Parser's process_empty_scalar method to raise an error:

import yaml

yaml_str = """\
- 1
- - 2
  -
  - 3
"""

def pes(*args, **kw):
    raise NotImplementedError

yaml.parser.Parser.process_empty_scalar = pes

data = yaml.safe_load(yaml_str)

print(data)

The above raises an error, if you comment out the assignment to .process_empty_scalar it parses correct.

Please note:

• layers in YAML do not necessarily mean python dicts will be formed
• you are using .load which is documented to be unsafe and almost guaranteed to be inappropriate.