instantiating pvsys, if pvmods given but not pvconst, then modules pvconst is different from strings and pvsys

[mikofski]

PVMismatch/pvmismatch/pvmismatch_lib/pvsystem.py

Lines 39 to 45 in 3f88910

	except AttributeError:
	# try to use the pvconst arg or create one if none
	if not pvconst:
	pvconst = PVconstants()
	# create a pvstring
	pvstrs = PVstring(numberMods=numberMods, pvmods=pvmods,
	pvconst=pvconst)

Should we check modules first and then copy pvconst from there? Which takes precedence? No, actually we don't need to because when a string is instantiated, it checks already to see if the modules have defined a pvconst and cascade it down

The trouble actually starts further down here:

PVMismatch/pvmismatch/pvmismatch_lib/pvsystem.py

Line 57 in 3f88910

self.pvconst = pvconst #: ``PVconstants`` used in ``PVsystem``

This is an issue because on L41-42 we created a new default pvconst and then passed it to the string which ignores it because the pvconst in pvmods tool precedence - whether it should or not's a different issue. But then on L57 we don't use the pvconst from the new string instead we take the default one, and voila 2 different pvconst.

IMO, the code in both pvsystem and pvstring seem to indicate that if a module or string is given, then it must have a pvconst, and that should take precedence. I think we should stick with that paradigm, so in that case, let the system instantiation go all the way to the bottom and then grab the single pvconst used everywhere for each component on the way back up. This would require changes to both pvsystem:

    def __init__(self, pvconst=None, numberStrs=NUMBERSTRS,
                 pvstrs=None, numberMods=NUMBERMODS, pvmods=None):
        # is pvstrs a list?
        try:
            pvstr0 = pvstrs[0]
        except TypeError:
            # is pvstrs a PVstring object?
            try:
                pvconst = pvstrs.pvconst
            except AttributeError:
                # create a pvstring
                pvstrs = PVstring(numberMods=numberMods, pvmods=pvmods,
                                  pvconst=pvconst)
                # pvconstants from the string takes precedence
                pvconst = pvstrs.pvconst
            # expand pvstrs to list
            pvstrs = [pvstrs] * numberStrs
            numberMods = [numberMods] * numberStrs
        else:
            pvconst = pvstr0.pvconst
            numberStrs = len(pvstrs)
            numberMods = []
            for p in pvstrs:
                if p.pvconst is not pvconst:
                    raise Exception('pvconst must be the same for all strings')
                numberMods.append(len(p.pvmods))
        self.pvconst = pvconst  #: ``PVconstants`` used in ``PVsystem``

and pvstring:

class PVstring(object):
    """
    A class for PV strings.

    :param numberMods: number of modules in string
    :param pvmods: either a list of modules, an instance of
        :class:`~pvmismatch.pvmismatch_lib.pvmodule.PVmodule` [Optional]
    :type pvmods: list, :class:`~pvmismatch.pvmismatch_lib.pvmodule.PVmodule`
    :param pvconst: a configuration constants object
    """
    def __init__(self, numberMods=NUMBERMODS, pvmods=None,
                 pvconst=None):
        # is pvmods a list?
        try:
            pvmod0 = pvmods[0]
        except TypeError:
            # is pvmods an object?
            try:
                pvconst = pvmods.pvconst
            except AttributeError:
                # create pvmod
                pvmods = PVmodule(pvconst=pvconst)
                # pvconstants from the module takes precedence
                pvconst = pvmods.pvconst
            # expand pvmods to list
            pvmods = [pvmods] * numberMods
        else:
            pvconst = pvmod0.pvconst
            numberMods = len(pvmods)
            for p in pvmods:
                if p.pvconst is not pvconst:
                    raise Exception('pvconst must be the same for all modules')
        self.pvconst = pvconst  #: ``PVconstants`` used in  ``PVstring``

related issues:

• The pvconst parameter is different for PV modules even though they are created in exactly same way. #119
• PVconst behavior #38
• BUG: pvconst is not a singleton, inconsistent, doesn't update (GH38) #62

not related:

• split pvconst into pvcell and configs to facilitate individual cell props #12
• remove local versions of pvconst, to make sure that different pvconst can be used #11