newSwitchAct with multiple enum parameters

[felixpollet]

It would be nice to be able to implement a switch activity that combines multiple enum parameters for the selection of other activities.
For example, rather than creating a first switch activity switch_act_1 controlled by switch_param_1 that points to switch_act_2a and switch_act_2b both of which are controlled by parameter switch_param_2, it could be possible to create a single multi_switch_act controlled by the combination of switch_param_1 and switch_param_2.

Here is an example :

multi_switch_act = newMultiSwitchAct(MYDB, "MultiSwitchAct", [switchParam1, switchParam2], {
    ("switchParam1_val1", switchParam2_val1) : act1  # act1 is selected if both switchParam1 = switchParam1_val1 and switchParam2 = switchParam2_val1
    ("switchParam1_val2", switchParam2_val2) : (act2, 0.4)  # act2 is selected if both switchParam1 = switchParam1_val2 and switchParam2 = switchParam2_val2
    ("switchParam1_val1", switchParam2_val2) : (act3, b + 6)  # act3 is selected if both switchParam1 = switchParam1_val1 and switchParam2 = switchParam2_val2
}

This could be done by modifying the newSwitchAct() method as follows:

def newMultiSwitchAct(dbname, name, paramDefList: Union[List[ParamDef], ParamDef], acts_dict: Union[Dict[str, ActivityOrActivityAmount], Dict[Tuple[str], ActivityOrActivityAmount]]):
    exch = defaultdict(lambda: 0)

    unit = None
    for key, act in acts_dict.items():
        amount = 1
        if isinstance(act, (list, tuple)):
            act, amount = act
        if isinstance(paramDefList, list):  # <-- this is new
            exch[act] += amount * reduce(lambda x, y: x*y, [paramDef.symbol(key[i]) for i, paramDef in enumerate(paramDefList)])
        else:  # <-- regular switch activity
            exch[act] += amount * paramDefList.symbol(key)
        unit = act["unit"]

    res = newActivity(dbname, name, unit=unit, exchanges=exch)

    return res

This should work for any number of enum parameters (not only two).