DynamoDB in examples, Example 2: Unique page views

import re
import uuid

from example_1 import DDBTable, DDBField, AmazonException


DDB_LOCAL_URL = 'http://localhost:8010'


class DDBUUID_UUIDField(DDBField):

    AMAZON_TYPE = 'S'
    _VALUE_REGEXP = re.compile('[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}_[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}')

    @classmethod
    def _validate(cls, value):
        if not isinstance(value, str):
            value = str(value)
        if cls._VALUE_REGEXP.match(value) is None:
            raise ValueError('UUID_UUID required.')
        return value


class DDBPageView(DDBTable):

    TABLE_NAME = 'page_view'
    KEY_SCHEMA = [{
        'AttributeName': 'page_id_user_id',
        'KeyType': 'HASH',
    }]
    PROVISIONED_THROUGHPUT = {
        'ReadCapacityUnits': 1,
        'WriteCapacityUnits': 1
    }
    FIELDS = {
        'page_id_user_id': DDBUUID_UUIDField,
    }

    def _get_endpoint_url(self):
        return DDB_LOCAL_URL

    def view(self, page_id, user_id):
        """ Returns True if item was created, else: returns False """
        page_id_user_id = '{page_id}_{user_id}'.format(page_id=page_id, user_id=user_id)
        try:
            self._dynamodb(operation='PutItem').call(
                TableName=self._get_table_name(),
                Item=self.encode_item(data={'page_id_user_id': page_id_user_id}),
                ConditionExpression='attribute_not_exists(page_id_user_id)')
        except AmazonException as e:
            if e.code == 'ConditionalCheckFailedException':
                return False # already exists
            raise e
        return True

    def check(self, page_id, user_id):
        page_id_user_id = '{page_id}_{user_id}'.format(page_id=page_id, user_id=user_id)
        response = self._dynamodb(operation='GetItem').call(
            TableName=self._get_table_name(),
            Key=self.encode_item(data={'page_id_user_id': page_id_user_id}))
        return 'Item' in response


if __name__ == '__main__':
    page_view = DDBPageView()
    page_view.create_table()
    page_id = uuid.uuid4()
    user_id = uuid.uuid4()
    print(page_view.view(page_id=page_id, user_id=user_id))
    print(page_view.view(page_id=page_id, user_id=user_id))
    print(page_view.check(page_id=page_id, user_id=user_id))
    user_id = uuid.uuid4()
    print(page_view.check(page_id=page_id, user_id=user_id))

    # True
    # False
    # True
    # False