REFACTOR payment: enforce Decimal type

FabLabKasse/UI/PayupCashDialogCode.py

@@ -29,6 +29,9 @@ class PayupCashDialog(QtGui.QDialog, Ui_PayupCashDialog):
     def __init__(self, parent, amount_total, cfg):
         """
         payment method dialog for automatic cash payin and payout
+        :param parent: parent widget passed on to QtGui.QDialog
+        :param amount_total: amount to pay
+        :type amount_total: Decimal
         :param cfg: config from ScriptHelper.getConfig()
         """
         QtGui.QDialog.__init__(self, parent)
@@ -49,6 +52,7 @@ def __init__(self, parent, amount_total, cfg):
         self.pushButton_acceptLowPayout.setVisible(False)
         self.pushButton_receipt.setVisible(False)
         self.pushButton_receipt.clicked.connect(self.accept_and_print_receipt)
+        assert isinstance(amount_total,  Decimal)
         assert amount_total % Decimal("0.01") == 0
         self.centsToPay = int(100 * amount_total)
         self.centsToPayOut = None

FabLabKasse/shopping/payment_methods.py

@@ -57,10 +57,10 @@ class AbstractPaymentMethod(object):
     __metaclass__ = ABCMeta
 
     def __init__(self, parent, shopping_backend, amount_to_pay, cfg):
-
         self.parent = parent
         self.shopping_backend = shopping_backend
         self.amount_to_pay = amount_to_pay
+        assert isinstance(amount_to_pay,  Decimal)
         self.cfg = cfg
         self.successful = None
         self.amount_paid = None
@@ -172,6 +172,8 @@ def execute_and_store(self):
           If possible, only override _show_dialog and not this method.
         """
         self._show_dialog()
+        assert isinstance(self.amount_paid,  (Decimal,  int))
+        assert isinstance(self.amount_returned,  (Decimal,  int))
         assert self.amount_paid >= self.amount_returned
         if self.successful:
             assert self.amount_paid >= self.amount_to_pay