A little help with template functions in a composite column, please!

[mopkin]

I am not a programmer, and I am stuck with the template in a custom column I am trying to create. I was hoping, someone here could help me.

I have 2 custom columns which I use as source of data for the third column. Column_1 is looking for PDFs in book formats, and when PDF is not present, returns N/A. Here's the expression: {formats:contains(PDF, , N/A)}

Column_2 is a regular text column with permitted values, which has only one value: Yes. (Or empty, if it's a No). This is a "manual" column, where I myself select Yes when needed.

Column_3 derives its values from the first two columns, either Yes, or N/A. I used the example of a relevant expression in the Calibre Manual online and came up with this: {#column_2:'ifempty($, field('#column_1'))'}. It works perfectly fine, correctly returning either Yes, or N/A, or empty.

What I am struggling with, is the empty in Column_3. I would like it to say No, so that the column always has a value, either Yes, or No, or N/A. But as I said, I am not a programmer, so I wasn't able to fix the expression for column_3, so it would return a No when Column_2 is empty.

It is always possible to add a No to Column_2, but I would rather avoid it, because Yes is a very rare occurrence, and it would mean I would have to manually add a No to every other book, when there might be a much easier solution. I would really appreciate if someone with the knowledge of Python (I am assuming, the expression above is in Python) could help me out with this.

[chaley]

First, the template language isn't python. It is something I made up.

It seems that the empty value is coming from #column_1. If I am right then this template should work.

{:'first_non_empty(field('#column_2'), field('#column_1'), 'No')'}

It says use #column_2 if it has a value, otherwise use #column_1 if it has a value, otherwise return 'No'.

[mopkin]

Thank you so much Charles! It works perfectly!