Update attribute "timestamp" reserved word

Question

You can work around this problem using expression attribute names (similar to the ExpressionAttributeValues you are already using).

table.update_item(
  Key={
    'id': item_id
  },
  UpdateExpression='SET #ts = :val1',
  ExpressionAttributeValues={
    ":val1": new_timestamp
  },
  ExpressionAttributeNames={
    "#ts": "timestamp"
  }
)

Read all about it here: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/Expressions.ExpressionAttributeNames.html