python3 dynamoDB Update_item do not work

I just practice using example code in AWS dynamoDB But, update code do not work with error

botocore.exceptions.ClientError: An error occurred (ValidationException) when calling the UpdateItem operation: The document path provided in the update expression is invalid for update

My python code is here. I could update DB without 'map' attribute.

table = dynamodb.Table('Movies')

title = "The Big New Movie"
year = 2015

response = table.update_item(
    Key={
        "year": year,
        "title": title
    },
    UpdateExpression="set #attrName.rating = :r, #attrName.plot=:p",
    ExpressionAttributeNames = {
        "#attrName" : "info"
    },
    ExpressionAttributeValues={
        ':r': decimal.Decimal(5.5),
        ':p': "Everything happens all at once."
    },
    ReturnValues="UPDATED_NEW"
)