Validate a JSON object

Parsing and validation are separate steps

Use json.loads() to parse the text, check for an object root, then validate its fields. Invalid JSON and a valid JSON object with incorrect fields fail at different boundaries.

import json
from zodify import validate

def read_user(text):
    data = json.loads(text)
    if type(data) is not dict:
        raise ValueError("Expected a JSON object")
    return validate({"name": str, "age": int}, data)

assert read_user('{"name":"Ada","age":36}')["age"] == 36
for invalid in ['[]', '{"name":"Ada","age":"36"}', '{"name":']:
    try:
        read_user(invalid)
    except ValueError:  # Includes JSONDecodeError.
        pass
    else:
        raise AssertionError("Expected parsing or validation failure")
print("json-object-validation: passed")

This is a Python object contract

The standard parser keeps the last duplicate object key and accepts non-finite numeric constants by default. This recipe does not promise duplicate-key rejection, strict JSON-number policy, or JSON Schema equivalence. Set input-size limits before parsing untrusted payloads.

The int schema rejects a parsed 1.0 because it is a Python float. For a JSON Schema contract, use a JSON Schema validator. A validate_json helper and export API are not in the documented release.

• Exact integers and JSON Schema →
• Selection guide →