How to validate structure (or schema) of dictionary in Python?

Question

I have a dictionary with config info:

my_conf = {
    'version': 1,

    'info': {
        'conf_one': 2.5,
        'conf_two': 'foo',
        'conf_three': False,
        'optional_conf': 'bar'
    }
}

I want to check if the dictionary follows the structure I need.

I'm looking for something like this:

conf_structure = {
    'version': int,

    'info': {
        'conf_one': float,
        'conf_two': str,
        'conf_three': bool
    }
}

is_ok = check_structure(conf_structure, my_conf)

Is there any solution done to this problem or any library that could make implementing check_structure more easy?

Answer 1

Without using libraries, you could also define a simple recursive function like this:

def check_structure(struct, conf):
    if isinstance(struct, dict) and isinstance(conf, dict):
        # struct is a dict of types or other dicts
        return all(k in conf and check_structure(struct[k], conf[k]) for k in struct)
    if isinstance(struct, list) and isinstance(conf, list):
        # struct is list in the form [type or dict]
        return all(check_structure(struct[0], c) for c in conf)
    elif isinstance(conf, type):
        # struct is the type of conf
        return isinstance(struct, conf)
    else:
        # struct is neither a dict, nor list, not type
        return False

This assumes that the config can have keys that are not in your structure, as in your example.

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Update: New version also supports lists, e.g. like 'foo': [{'bar': int}]