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Python JSON schema validator with better error message

Project description

kanpai is a library for validating Python data structures, mainly those converted from JSON. e.g. JSON received from api request, obtained from config file etc. The library is built with a focus on better error message. e.g. when validating a dict(which may be converted from JSON), in case of error, Kanpai returns a dict with error details against each keys


Here is a quick example

from kanpai import Kanpai

schema = Kanpai.Object({
        'first_name': (Kanpai.String(error='User first name must be string.')
                       .required(error='Please provide user first name.')
                       .max(256, error='Maximum allowed length is 256')),

        'last_name': (Kanpai.String(error='User last name must be a String')
                      .required(error='Please provide user last name.')),

        'age'      : (Kanpai.Number(error='Age must be a number.')
                      .max(35,'Maximum allowed age is 35')
                      .min(18,'Age must be minimum 18'))


validation_result = schema.validate({
  'age': 15

assert validation_result == {
  'success': False,
  'error': {
    'last_name': 'Please provide user last name.',
    'age': 'Age must be minimum 18'
  'data': {
     'age': 15


Use pip

pip install kanpai


Validators are the building blocks for Kanpai library. There are validators for different types of data. e.g. String, Array, Object etc. All validators are accessible from Kanpai namespace.

from kanpai import Kanpai


Validation rules can be applied on a validator instance by calling rule methods. All rule method returns self. So method calls can be chained. During validaton the rules are checked in order they are applied during validator construction.

Every validator returns an instance of Validator class which has a method called validate. Validate takes data to be validated as input and return a dictionary obejct containing:

 'success':'Boolean - Whether validation is success or not',
 'error': 'validation error',
 'data':'Incase of error data provided for validation, in case success validated data

After creating a validator it can be configured to apply validation rule by calling its rule methods. After constructing a validator it can be used for multiple validation safely.

For more details on individual validators and its rule methods please refer corresponding file in docs folder.

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