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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def validate_txn_obj(obj_name, obj, key, validation_fun):
 """Validate value of `key` in `obj` using `validation_fun`. Args: obj_name (str):
 name for `obj` being validated. obj (dict):
 dictionary object. key (str):
 key to be validated in `obj`. validation_fun (function):
 function used to validate the value of `key`. Returns: None: indicates validation successful Raises: ValidationError: `validation_fun` will raise exception on failure """

    backend = bigchaindb.config['database']['backend']

    if backend == 'localmongodb':
        data = obj.get(key, {})
        if isinstance(data, dict):
            validate_all_keys_in_obj(obj_name, data, validation_fun)
        elif isinstance(data, list):
            validate_all_items_in_list(obj_name, data, validation_fun)