ENH: BUG: add _calc_now flag to determine when cell is recalculated (GH59)

pvmismatch/pvmismatch_lib/pvcell.py

@@ -47,6 +47,9 @@ class PVcell(object):
     :param pvconst: configuration constants object
     :type pvconst: :class:`~pvmismatch.pvmismatch_lib.pvconstants.PVconstants`
     """
+
+    _calc_now = False  #: if True ``calcCells()`` is called in ``__setattr__``
+
     def __init__(self, Rs=RS, Rsh=RSH, Isat1_T0=ISAT1_T0, Isat2=ISAT2,
                  Isc0_T0=ISC0_T0, aRBD=ARBD, bRBD=BRBD, VRBD=VRBD_,
                  nRBD=NRBD, Eg=EG, alpha_Isc=ALPHA_ISC,
@@ -69,6 +72,8 @@ def __init__(self, Rs=RS, Rsh=RSH, Isat1_T0=ISAT1_T0, Isat2=ISAT2,
         self.Icell = None  #: cell currents on IV curve [A]
         self.Vcell = None  #: cell voltages on IV curve [V]
         self.Pcell = None  #: cell power on IV curve [W]
+        # set calculation flag
+        self._calc_now = True  # overwrites the class attribute
 
     def __str__(self):
         fmt = '<PVcell(Ee=%g[suns], Tcell=%g[K], Isc=%g[A], Voc=%g[V])>'
@@ -78,27 +83,28 @@ def __repr__(self):
         return str(self)
 
     def __setattr__(self, key, value):
+        # check for floats
         try:
             value = np.float64(value)
         except (TypeError, ValueError):
-            pass
+            pass  # fail silently if not float, eg: pvconst or _calc_now
         super(PVcell, self).__setattr__(key, value)
-        # after all attributes have been initialized, recalculate IV curve
-        # every time __setattr__() is called
-        if hasattr(self, 'pvconst'):
+        # recalculate IV curve
+        if self._calc_now:
             Icell, Vcell, Pcell = self.calcCell()
-            super(PVcell, self).__setattr__('Icell', Icell)
-            super(PVcell, self).__setattr__('Vcell', Vcell)
-            super(PVcell, self).__setattr__('Pcell', Pcell)
+            self.__dict__.update(Icell=Icell, Vcell=Vcell, Pcell=Pcell)
 
     def update(self, **kwargs):
         """
         Update user-defined constants.
         """
-        # TODO: use __dict__.update(), check for floats and update IV curve
-        # self.__dict__.update(kwargs)
+        # turn off calculation flag until all attributes are updated
+        self._calc_now = False
+        # don't use __dict__.update() instead use setattr() to go through
+        # custom __setattr__() so that numbers are cast to floats
         for k, v in iteritems(kwargs):
             setattr(self, k, v)
+        self._calc_now = True  # recalculate
 
     @property
     def Vt(self):
@@ -276,4 +282,4 @@ def plot(self):
         plt.xlim(0, self.Voc)
         plt.ylim(0, (self.Isc + 1) * self.Voc)
         plt.grid()
-        return cell_plot
+        return cell_plot

pvmismatch/pvmismatch_lib/pvmodule.py

@@ -174,10 +174,8 @@ def __init__(self, cell_pos=STD96, pvcells=None, pvconst=PVconstants(),
         self.Vbypass = Vbypass  #: [V] trigger voltage of bypass diode
         self.cellArea = cellArea  #: [cm^2] cell area
         if pvcells is None:
-            # faster to use copy instead of making each object in a for-loop
-            # use copy instead of deepcopy to keep same pvconst for all objects
-            # PVcell.calcCell() creates new np.ndarray if attributes change
             pvcells = PVcell(pvconst=self.pvconst)
+        # expand pvcells to list
         if isinstance(pvcells, PVcell):
             pvcells = [pvcells] * self.numberCells
         if len(pvcells) != self.numberCells:

pvmismatch/pvmismatch_lib/pvstring.py

@@ -30,18 +30,21 @@ def __init__(self, numberMods=NUMBERMODS, pvmods=None,
         self.pvconst = pvconst
         self.numberMods = numberMods
         if pvmods is None:
-            # use deepcopy instead of making each object in for-loop, 2x faster
             pvmods = PVmodule(pvconst=self.pvconst)
+        # expand pvmods to list
         if isinstance(pvmods, PVmodule):
             pvmods = [pvmods] * self.numberMods
-            # reset pvconsts in all pvcells and pvmodules
-            for p in pvmods:
-                for c in p.pvcells:
-                    c.pvconst = self.pvconst
-                p.pvconst = self.pvconst
         if len(pvmods) != self.numberMods:
             # TODO: use pvmismatch exceptions
             raise Exception("Number of modules doesn't match.")
+        # check that pvconst if given, is the same for all cells
+        # don't assign pvcell.pvconst here since it triggers a recalc
+        for p in pvmods:
+            for c in p.pvcells:
+                if c.pvconst is not self.pvconst:
+                    raise Exception('PVconstant must be the same for all cells')
+            if p.pvconst is not self.pvconst:
+                raise Exception('PVconstant must be the same for all cells')
         self.pvmods = pvmods
         self.Istring, self.Vstring, self.Pstring = self.calcString()
 

pvmismatch/pvmismatch_lib/pvsystem.py

@@ -35,7 +35,7 @@ def __init__(self, pvconst=PVconstants(), numberStrs=NUMBERSTRS,
         if pvstrs is None:
             pvstrs = PVstring(numberMods=self.numberMods, pvmods=pvmods,
                               pvconst=self.pvconst)
-        # use deep copy instead of making each object in a for-loop
+        # expand pvstrs to list
         if isinstance(pvstrs, PVstring):
             pvstrs = [pvstrs] * self.numberStrs
         if len(pvstrs) != self.numberStrs:

pvmismatch/tests/test_pvcell.py

@@ -69,6 +69,21 @@ def test_pvcell_calc_rbd():
     pvc2 = PVcell(bRBD=-0.056)
     ok_(isinstance(pvc2, PVcell))
 
-
+
+def test_pvcell_calc_now_flag():
+    pvc = PVcell()
+    itest, vtest, ptest = pvc.Icell, pvc.Vcell, pvc.Pcell
+    pvc._calc_now = False
+    pvc.Rs = 0.001
+    assert np.allclose(itest, pvc.Icell)
+    assert np.allclose(vtest, pvc.Vcell)
+    assert np.allclose(ptest, pvc.Pcell)
+    icell, vcell, pcell = pvc.calcCell()
+    pvc._calc_now = True
+    assert np.allclose(icell, pvc.Icell)
+    assert np.allclose(vcell, pvc.Vcell)
+    assert np.allclose(pcell, pvc.Pcell)
+
+
 if __name__ == "__main__":
     test_calc_series()