Doctype autoname expression

Hi to all,
I defined a new doctype, I’m trying to set a naming rule as an expression.

If I understand well, in the Autoname field I have to write the expression in Jinja language.

I need a substring of e field + Year month of a date + another field.
I used thi formula, and I try also using single bracket

{{ category[:3].upper() }}+{{transaction_date.strftime('%Y%m')}}_{tipo_doc}

but in the sql table, i see that only {tipo_doc} was valorized correctly the rest of formula was saved as string instead of calculate the expression.

Where is the error?Any suggestion?


I suggest applying via the Controller Method so please check this.