How to use the calliope.core.preprocess.util.constraint_exists function in calliope

constraint_sets['techs_energy_capacity_systemwide_constraint'] = [
        i for i in sets.techs
        if model_run.get_key('techs.{}.constraints.energy_cap_max_systemwide'.format(i), None)
        or model_run.get_key('techs.{}.constraints.energy_cap_equals_systemwide'.format(i), None)
    ]

    # dispatch.py
    constraint_sets['loc_tech_carriers_carrier_production_max_constraint'] = [
        i for i in sets.loc_tech_carriers_prod
        if i not in sets.loc_tech_carriers_conversion_plus
        and i.rsplit('::', 1)[0] not in sets.loc_techs_milp
    ]
    constraint_sets['loc_tech_carriers_carrier_production_min_constraint'] = [
        i for i in sets.loc_tech_carriers_prod
        if i not in sets.loc_tech_carriers_conversion_plus
        and constraint_exists(model_run, i.rsplit('::', 1)[0], 'constraints.energy_cap_min_use')
        and i.rsplit('::', 1)[0] not in sets.loc_techs_milp
    ]
    constraint_sets['loc_tech_carriers_carrier_consumption_max_constraint'] = [
        i for i in sets.loc_tech_carriers_con
        if i.rsplit('::', 1)[0] in sets.loc_techs_demand +
            sets.loc_techs_storage + sets.loc_techs_transmission
        and i.rsplit('::', 1)[0] not in sets.loc_techs_milp
    ]
    constraint_sets['loc_techs_resource_max_constraint'] = sets.loc_techs_supply_plus
    constraint_sets['loc_tech_carriers_ramping_constraint'] = [
        i for i in sets.loc_tech_carriers_prod
        if i.rsplit('::', 1)[0] in sets.loc_techs_ramping
    ]
    # clustering-specific dispatch constraints
    if (model_run.model.get_key('time.function', None) == 'apply_clustering' and
            model_run.model.get_key('time.function_options.storage_inter_cluster', True)):

if i.rsplit('::', 1)[0] in sets.loc_techs_demand +
            sets.loc_techs_storage + sets.loc_techs_transmission
        and i.rsplit('::', 1)[0] in sets.loc_techs_milp
    ]
    constraint_sets['loc_techs_energy_capacity_units_milp_constraint'] = [
        i for i in sets.loc_techs_milp
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_unit')
        is not None
    ]
    constraint_sets['loc_techs_storage_capacity_units_milp_constraint'] = [
        i for i in sets.loc_techs_milp if i in sets.loc_techs_store
    ]
    constraint_sets['loc_techs_energy_capacity_max_purchase_milp_constraint'] = [
        i for i in sets.loc_techs_purchase
        if (constraint_exists(model_run, i, 'constraints.energy_cap_equals') is not None
            or (constraint_exists(model_run, i, 'constraints.energy_cap_max') is not None
                and constraint_exists(model_run, i, 'constraints.energy_cap_max') != np.inf))
    ]
    constraint_sets['loc_techs_energy_capacity_min_purchase_milp_constraint'] = [
        i for i in sets.loc_techs_purchase
        if (not constraint_exists(model_run, i, 'constraints.energy_cap_equals')
            and constraint_exists(model_run, i, 'constraints.energy_cap_min'))
    ]
    constraint_sets['loc_techs_storage_capacity_max_purchase_milp_constraint'] = [
        i for i in set(sets.loc_techs_purchase).intersection(sets.loc_techs_store)
        if (constraint_exists(model_run, i, 'constraints.storage_cap_equals') is not None
            or (constraint_exists(model_run, i, 'constraints.storage_cap_max') is not None
                and constraint_exists(model_run, i, 'constraints.storage_cap_max') != np.inf))
    ]
    constraint_sets['loc_techs_storage_capacity_min_purchase_milp_constraint'] = [
        i for i in set(sets.loc_techs_purchase).intersection(sets.loc_techs_store)
        if (not constraint_exists(model_run, i, 'constraints.storage_cap_equals')

and i.rsplit('::', 1)[0] in sets.loc_techs_milp
    ]
    constraint_sets['loc_techs_carrier_production_min_conversion_plus_milp_constraint'] = [
        i for i in sets.loc_techs_conversion_plus
        if constraint_exists(model_run, i, 'constraints.energy_cap_min_use')
        and i in sets.loc_techs_milp
    ]
    constraint_sets['loc_tech_carriers_carrier_consumption_max_milp_constraint'] = [
        i for i in sets.loc_tech_carriers_con
        if i.rsplit('::', 1)[0] in sets.loc_techs_demand +
            sets.loc_techs_storage + sets.loc_techs_transmission
        and i.rsplit('::', 1)[0] in sets.loc_techs_milp
    ]
    constraint_sets['loc_techs_energy_capacity_units_milp_constraint'] = [
        i for i in sets.loc_techs_milp
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_unit')
        is not None
    ]
    constraint_sets['loc_techs_storage_capacity_units_milp_constraint'] = [
        i for i in sets.loc_techs_milp if i in sets.loc_techs_store
    ]
    constraint_sets['loc_techs_energy_capacity_max_purchase_milp_constraint'] = [
        i for i in sets.loc_techs_purchase
        if (constraint_exists(model_run, i, 'constraints.energy_cap_equals') is not None
            or (constraint_exists(model_run, i, 'constraints.energy_cap_max') is not None
                and constraint_exists(model_run, i, 'constraints.energy_cap_max') != np.inf))
    ]
    constraint_sets['loc_techs_energy_capacity_min_purchase_milp_constraint'] = [
        i for i in sets.loc_techs_purchase
        if (not constraint_exists(model_run, i, 'constraints.energy_cap_equals')
            and constraint_exists(model_run, i, 'constraints.energy_cap_min'))
    ]

i for i in sets.loc_techs_milp
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_unit')
        is not None
    ]
    constraint_sets['loc_techs_storage_capacity_units_milp_constraint'] = [
        i for i in sets.loc_techs_milp if i in sets.loc_techs_store
    ]
    constraint_sets['loc_techs_energy_capacity_max_purchase_milp_constraint'] = [
        i for i in sets.loc_techs_purchase
        if (constraint_exists(model_run, i, 'constraints.energy_cap_equals') is not None
            or (constraint_exists(model_run, i, 'constraints.energy_cap_max') is not None
                and constraint_exists(model_run, i, 'constraints.energy_cap_max') != np.inf))
    ]
    constraint_sets['loc_techs_energy_capacity_min_purchase_milp_constraint'] = [
        i for i in sets.loc_techs_purchase
        if (not constraint_exists(model_run, i, 'constraints.energy_cap_equals')
            and constraint_exists(model_run, i, 'constraints.energy_cap_min'))
    ]
    constraint_sets['loc_techs_storage_capacity_max_purchase_milp_constraint'] = [
        i for i in set(sets.loc_techs_purchase).intersection(sets.loc_techs_store)
        if (constraint_exists(model_run, i, 'constraints.storage_cap_equals') is not None
            or (constraint_exists(model_run, i, 'constraints.storage_cap_max') is not None
                and constraint_exists(model_run, i, 'constraints.storage_cap_max') != np.inf))
    ]
    constraint_sets['loc_techs_storage_capacity_min_purchase_milp_constraint'] = [
        i for i in set(sets.loc_techs_purchase).intersection(sets.loc_techs_store)
        if (not constraint_exists(model_run, i, 'constraints.storage_cap_equals')
            and constraint_exists(model_run, i, 'constraints.storage_cap_min'))
    ]
    constraint_sets['loc_techs_update_costs_investment_units_milp_constraint'] = [
        i for i in sets.loc_techs_milp
        if i in sets.loc_techs_investment_cost and

if constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_equals')
    ]
    constraint_sets['loc_techs_energy_capacity_storage_min_constraint'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_min')
        and not constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_equals')
    ]
    constraint_sets['loc_techs_energy_capacity_storage_max_constraint'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_max')
        and not constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_equals')
    ]
    constraint_sets['loc_techs_resource_capacity_constraint'] = [
        i for i in sets.loc_techs_finite_resource_supply_plus
        if any([
            constraint_exists(model_run, i, 'constraints.resource_cap_equals'),
            constraint_exists(model_run, i, 'constraints.resource_cap_max'),
            constraint_exists(model_run, i, 'constraints.resource_cap_min')
        ])
    ]
    constraint_sets['loc_techs_resource_capacity_equals_energy_capacity_constraint'] = [
        i for i in sets.loc_techs_finite_resource_supply_plus
        if constraint_exists(model_run, i, 'constraints.resource_cap_equals_energy_cap')
    ]
    constraint_sets['loc_techs_resource_area_constraint'] = sets.loc_techs_area
    constraint_sets['loc_techs_resource_area_per_energy_capacity_constraint'] = [
        i for i in sets.loc_techs_area
        if constraint_exists(model_run, i, 'constraints.resource_area_per_energy_cap')
        is not None
    ]
    constraint_sets['locs_resource_area_capacity_per_loc_constraint'] = [
        i for i in sets.locs

]
    constraint_sets['loc_techs_energy_capacity_storage_min_constraint'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_min')
        and not constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_equals')
    ]
    constraint_sets['loc_techs_energy_capacity_storage_max_constraint'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_max')
        and not constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_equals')
    ]
    constraint_sets['loc_techs_resource_capacity_constraint'] = [
        i for i in sets.loc_techs_finite_resource_supply_plus
        if any([
            constraint_exists(model_run, i, 'constraints.resource_cap_equals'),
            constraint_exists(model_run, i, 'constraints.resource_cap_max'),
            constraint_exists(model_run, i, 'constraints.resource_cap_min')
        ])
    ]
    constraint_sets['loc_techs_resource_capacity_equals_energy_capacity_constraint'] = [
        i for i in sets.loc_techs_finite_resource_supply_plus
        if constraint_exists(model_run, i, 'constraints.resource_cap_equals_energy_cap')
    ]
    constraint_sets['loc_techs_resource_area_constraint'] = sets.loc_techs_area
    constraint_sets['loc_techs_resource_area_per_energy_capacity_constraint'] = [
        i for i in sets.loc_techs_area
        if constraint_exists(model_run, i, 'constraints.resource_area_per_energy_cap')
        is not None
    ]
    constraint_sets['locs_resource_area_capacity_per_loc_constraint'] = [
        i for i in sets.locs
        if model_run.locations[i].get_key('available_area', None) is not None

# capacity.py
    constraint_sets['loc_techs_storage_capacity_constraint'] = [
        i for i in sets.loc_techs_store if i not in sets.loc_techs_milp
    ]
    constraint_sets['loc_techs_energy_capacity_storage_constraint_old'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.charge_rate')
    ]
    constraint_sets['loc_techs_energy_capacity_storage_equals_constraint'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_equals')
    ]
    constraint_sets['loc_techs_energy_capacity_storage_min_constraint'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_min')
        and not constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_equals')
    ]
    constraint_sets['loc_techs_energy_capacity_storage_max_constraint'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_max')
        and not constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_equals')
    ]
    constraint_sets['loc_techs_resource_capacity_constraint'] = [
        i for i in sets.loc_techs_finite_resource_supply_plus
        if any([
            constraint_exists(model_run, i, 'constraints.resource_cap_equals'),
            constraint_exists(model_run, i, 'constraints.resource_cap_max'),
            constraint_exists(model_run, i, 'constraints.resource_cap_min')
        ])
    ]
    constraint_sets['loc_techs_resource_capacity_equals_energy_capacity_constraint'] = [

sets = model_run.sets
    ## From here on, everything is a `key=value` pair within a dictionary

    constraint_sets = dict()
    # energy_balance.py
    constraint_sets['loc_carriers_system_balance_constraint'] = sets.loc_carriers
    constraint_sets['loc_techs_balance_supply_constraint'] = sets.loc_techs_finite_resource_supply
    constraint_sets['loc_techs_balance_demand_constraint'] = sets.loc_techs_finite_resource_demand
    constraint_sets['loc_techs_resource_availability_supply_plus_constraint'] = sets.loc_techs_finite_resource_supply_plus
    constraint_sets['loc_techs_balance_transmission_constraint'] = sets.loc_techs_transmission
    constraint_sets['loc_techs_balance_supply_plus_constraint'] = sets.loc_techs_supply_plus
    constraint_sets['loc_techs_balance_storage_constraint'] = sets.loc_techs_storage
    if model_run.run.cyclic_storage is True:
        constraint_sets['loc_techs_storage_initial_constraint'] = [
            i for i in sets.loc_techs_store
            if constraint_exists(model_run, i, 'constraints.storage_initial') is not None
        ]
    constraint_sets['loc_techs_storage_discharge_depth'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.storage_discharge_depth')
    ]
    constraint_sets['carriers_reserve_margin_constraint'] = [
        i for i in sets.carriers
        if i in model_run.model.get_key('reserve_margin', {}).keys()
    ]
    # clustering-specific balance constraints
    if (model_run.model.get_key('time.function', None) == 'apply_clustering' and
            model_run.model.get_key('time.function_options.storage_inter_cluster', True)):
        set_name = 'loc_techs_balance_storage_inter_cluster_constraint'
        constraint_sets[set_name] = sets.loc_techs_store

    # costs.py

constraint_sets['loc_techs_energy_capacity_storage_max_constraint'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_max')
        and not constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_equals')
    ]
    constraint_sets['loc_techs_resource_capacity_constraint'] = [
        i for i in sets.loc_techs_finite_resource_supply_plus
        if any([
            constraint_exists(model_run, i, 'constraints.resource_cap_equals'),
            constraint_exists(model_run, i, 'constraints.resource_cap_max'),
            constraint_exists(model_run, i, 'constraints.resource_cap_min')
        ])
    ]
    constraint_sets['loc_techs_resource_capacity_equals_energy_capacity_constraint'] = [
        i for i in sets.loc_techs_finite_resource_supply_plus
        if constraint_exists(model_run, i, 'constraints.resource_cap_equals_energy_cap')
    ]
    constraint_sets['loc_techs_resource_area_constraint'] = sets.loc_techs_area
    constraint_sets['loc_techs_resource_area_per_energy_capacity_constraint'] = [
        i for i in sets.loc_techs_area
        if constraint_exists(model_run, i, 'constraints.resource_area_per_energy_cap')
        is not None
    ]
    constraint_sets['locs_resource_area_capacity_per_loc_constraint'] = [
        i for i in sets.locs
        if model_run.locations[i].get_key('available_area', None) is not None
        and sets.loc_techs_area
    ]
    constraint_sets['loc_techs_energy_capacity_constraint'] = [
        i for i in sets.loc_techs
        if i not in sets.loc_techs_milp + sets.loc_techs_purchase
    ]

constraint_sets['loc_techs_energy_capacity_storage_constraint_old'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.charge_rate')
    ]
    constraint_sets['loc_techs_energy_capacity_storage_equals_constraint'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_equals')
    ]
    constraint_sets['loc_techs_energy_capacity_storage_min_constraint'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_min')
        and not constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_equals')
    ]
    constraint_sets['loc_techs_energy_capacity_storage_max_constraint'] = [
        i for i in sets.loc_techs_store
        if constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_max')
        and not constraint_exists(model_run, i, 'constraints.energy_cap_per_storage_cap_equals')
    ]
    constraint_sets['loc_techs_resource_capacity_constraint'] = [
        i for i in sets.loc_techs_finite_resource_supply_plus
        if any([
            constraint_exists(model_run, i, 'constraints.resource_cap_equals'),
            constraint_exists(model_run, i, 'constraints.resource_cap_max'),
            constraint_exists(model_run, i, 'constraints.resource_cap_min')
        ])
    ]
    constraint_sets['loc_techs_resource_capacity_equals_energy_capacity_constraint'] = [
        i for i in sets.loc_techs_finite_resource_supply_plus
        if constraint_exists(model_run, i, 'constraints.resource_cap_equals_energy_cap')
    ]
    constraint_sets['loc_techs_resource_area_constraint'] = sets.loc_techs_area
    constraint_sets['loc_techs_resource_area_per_energy_capacity_constraint'] = [