Conditional string formatting in indicator metadata fields

[Zeitsperre]

Addressing a Problem?

Let's take an indicator that accepts None for a field:

degree_days_exceedance_date = Temp(
    ...
    description="Day of year when the integral of degree days (mean temperature {op} {thresh}) exceeds {sum_thresh}, "
    "with the cumulative sum starting from {after_date}.",
    ...
)

The description field will return:

"Day of year when the integral of degree days (mean temperature > 4 degc) exceeds 200 k days, with the cumulative sum starting from none."

Potential Solution

I haven't delved into the Indicator class code, but if we had access to the call signature keyword arguments, we could perform a string formatting on the fields containing {...} patterns.

This would allow us to provide conditional statements within the metadata fields.

Additional context

No response

Contribution

• I would be willing/able to open a Pull Request to contribute this feature.

Code of Conduct

• I agree to follow this project's Code of Conduct

[aulemahal]

This is one of the goals of #1120!

Currently you can pass a function to the indicator's definition, it will receive the pre-formatted arguments.
See

xclim/xclim/core/indicator.py

Lines 1223 to 1224 in 2d6896a

	if callable(val):
	val = val(**mba)

and lines above to see how mba is filled. But this solution is clunky and we almost never use it. And it is not feasible for the translations, while the jinja method could be!