def visit_rule(self, rule, (label, equals, expression)):
        expression.name = label  # Assign a name to the expr.
        return expression
Test aggregation: sum/cumulate (combined)
dataset/ETHPy150Open erikrose/parsimonious/parsimonious/grammar.py/RuleVisitor.visit_rule--crossover with--dataset/ETHPy150Open sahana/eden/modules/unit_tests/s3/s3timeplot.py/PeriodTests.testAggregateCumulate