Syntax Error on AWS DynamoDB Update_Item (lambda function)

Question

I am trying to update a current item in a dynamoDB table from a lambda function and am getting a syntax error with no information. I am baffled as I followed numerous online forums and blog posts to get to this stage, and the code seems identical. My put_item snippet works as intended so dynamoDB has been connected to the lambda function correctly. Any help would be really appreciated.

My code is as follows:

update = client.update_item(
        TableName='sample',
        Key={'id': {'S': body["id"]},
        UpdateExpression="set cancelled = :g",
        ConditionExpression = 'attribute_exists(id)',
        ExpressionAttributeValues={
            ':g': "yes"
        },
        ReturnValues="UPDATED_NEW"
)

The logs I get are as follows:

{
    "errorMessage": "Syntax error in module 'lambda_function': invalid syntax (lambda_function.py, line 89)",
    "errorType": "Runtime.UserCodeSyntaxError",
    "requestId": "86785a61-c526-4647-9a2c-b51466ddb8a6",
    "stackTrace": [
    "  File \"/var/task/lambda_function.py\" Line 89\n         UpdateExpression=\"set canceled = :g\",\n"
  ]
}

After resolving this, I get the following error

{
  "errorMessage": "Parameter validation failed:\nInvalid type for parameter ExpressionAttributeValues.:g, value: yes, type: <class 'str'>, valid types: <class 'dict'>",
  "errorType": "ParamValidationError",
  "requestId": "b7710541-b398-4f2f-9f67-7eaafb1426bc",
  "stackTrace": [
    "  File \"/var/task/lambda_function.py\", line 84, in lambda_handler\n    update = client.update_item(\n",
    "  File \"/var/runtime/botocore/client.py\", line 391, in _api_call\n    return self._make_api_call(operation_name, kwargs)\n",
    "  File \"/var/runtime/botocore/client.py\", line 691, in _make_api_call\n    request_dict = self._convert_to_request_dict(\n",
    "  File \"/var/runtime/botocore/client.py\", line 739, in _convert_to_request_dict\n    request_dict = self._serializer.serialize_to_request(\n",
    "  File \"/var/runtime/botocore/validate.py\", line 360, in serialize_to_request\n    raise ParamValidationError(report=report.generate_report())\n"
  ]
}

Answer 1

Looks like you're choosing to interact with DynamoDB at the lowest wire level so you need to pass the "S" string type hint:

":g": { "S": "yes" },

It can be confusing because you can interact with DynamoDB at various abstraction levels. I suggest going up a level and using .resource instead of .client .

Here's a sample where you don't need the "S" hints and things like that: https://github.com/aws-samples/aws-dynamodb-examples/blob/master/DynamoDB-SDK-Examples/python/WorkingWithItems/updating_item.py