[BUG] KeyError: 'operation' when processing Amon.tasmin (and related variables)

[rhaegar325]

Bug: KeyError: 'operation' when processing Amon.tasmin (and related variables)

Description

Processing Amon.tasmin fails with the following error:

Error processing Amon.tasmin: 'operation'

This is a KeyError raised in evaluate_expression() when it tries to access expr["operation"] on a calculation dict that uses "formula" as the function-name key instead.

Affected Variables

The following variables in ACCESS-ESM1.6_mappings.json use "formula" instead of "operation":

• tasmin — calculate_monthly_minimum
• tasmax — calculate_monthly_maximum
• areacello — calculate_areacello
• (ocean variable) — calculate_global_ave_ocean

Root Cause

In src/access_moppy/derivations/__init__.py, evaluate_expression() unconditionally accesses expr["operation"]:

# line 113 (before fix)
op = expr["operation"]

However, some mapping entries use "formula" as the key for the function name:

"calculation": {
    "type": "formula",
    "formula": "calculate_monthly_minimum",
    "operands": ["fld_s03i236"]
}

While others correctly use "operation":

"calculation": {
    "type": "formula",
    "operation": "add",
    "operands": ["fld_s30i405", "fld_s30i406"]
}

This inconsistency in ACCESS-ESM1.6_mappings.json causes evaluate_expression() to raise a KeyError for the affected variables.

Fix

Update evaluate_expression() to accept either "operation" or "formula" as the function-name key:

# src/access_moppy/derivations/__init__.py, line 113
op = expr.get("operation") or expr.get("formula")

or make the handling consistent in ACCESS-ESM1.6_mappings.json by using the operation.