What is PyQGIS equivalent code of expression "attribute(@atlas_feature, 'FIELD_NAME')"?

Question

I have a pretty long expression filter so it would be more neat to put it all in a function expression instead. So far, I just found that equivalent PyQGIS within function body tends to be ironically even longer, though.

I'm trying to find equivalent expression in PyQGIS of

attribute(@atlas_feature, 'FIELD_NAME')

Answer 1

The @atlas_feature is a variable which is provided in the expression context from the environment. Such variables are normally passed as parameters into functions, just like you are passing it here as a parameter to a function attribute.

You can do the same in your own function which then looks like this:

@qgsfunction(args=1, group='shorthands')
def get_atlas_attribute(atlasfeature, feature, parent):
    return atlasfeature['FIELD_NAME']

And you would call it like this

get_atlas_attribute(@atlas_feature)

I am not sure if this is of big help for you just as well as I am not sure what exactly you want to achieve.

I guess it's mostly about making your expressions more readable by delegating repeated code to a dedicated function. I think that's fine (although it adds another layer of potential failures).

I just found that equivalent PyQGIS within function body tends to be ironically even longer

That is very likely to be true. And I don't think there is anything ironic about it. The expression engine is built for this very purpose. Take yet another language and you will have even more code ;)