Passing a parameter value as a string using Python / Cypher

Hi

I just can't get the following. I'm using Google co-lab. The commented out line works as expected but after trying various options from threads I still can't get it. I'm just trying to pass the entity_type variable in after declaring it.

Also once this works I will then want to pass in the following so I assume it would be the same as the value passed to the get_slot method would also be a string entity_type = tracker.get_slot("entity_type")

Can anyone assist? Thanks.

Chris