1 files changed, 39 insertions, 35 deletions

diff --git a/talersurvey/survey/amount.py b/talersurvey/survey/amount.py
index 9a6318a..46e3446 100644
--- a/talersurvey/survey/amount.py
+++ b/talersurvey/survey/amount.py
@@ -23,43 +23,46 @@
 #  which might need it.
 
 class CurrencyMismatch(Exception):
-    pass
+    def __init__(self, curr1, curr2):
+        super(CurrencyMismatch, self).__init__(
+            "%s vs %s" % (curr1, curr2))
 
 class BadFormatAmount(Exception):
     def __init__(self, faulty_str):
-        self.faulty_str = faulty_str
+        super(BadFormatAmount, self).__init__(
+            "Bad format amount: " + faulty_str)
 
 class Amount:
     # How many "fraction" units make one "value" unit of currency
     # (Taler requires 10^8).  Do not change this 'constant'.
     @staticmethod
-    def FRACTION():
+    def _fraction():
         return 10 ** 8
 
     @staticmethod
-    def MAX_VALUE():
+    def _max_value():
         return (2 ** 53) - 1
 
     def __init__(self, currency, value=0, fraction=0):
         # type: (str, int, int) -> Amount
-        assert(value >= 0 and fraction >= 0)
+        assert value >= 0 and fraction >= 0
         self.value = value
         self.fraction = fraction
         self.currency = currency
         self.__normalize()
-        assert(self.value <= Amount.MAX_VALUE())
+        assert self.value <= Amount._max_value()
 
     # Normalize amount
     def __normalize(self):
-        if self.fraction >= Amount.FRACTION():
-            self.value += int(self.fraction / Amount.FRACTION())
-            self.fraction = self.fraction % Amount.FRACTION()
+        if self.fraction >= Amount._fraction():
+            self.value += int(self.fraction / Amount._fraction())
+            self.fraction = self.fraction % Amount._fraction()
 
     # Parse a string matching the format "A:B.C"
     # instantiating an amount object.
     @classmethod
     def parse(cls, amount_str):
-        exp = '^\s*([-_*A-Za-z0-9]+):([0-9]+)\.([0-9]+)\s*$'
+        exp = r'^\s*([-_*A-Za-z0-9]+):([0-9]+)\.([0-9]+)\s*$'
         import re
         parsed = re.search(exp, amount_str)
         if not parsed:
@@ -67,7 +70,7 @@ class Amount:
         value = int(parsed.group(2))
         fraction = 0
         for i, digit in enumerate(parsed.group(3)):
-            fraction += int(int(digit) * (Amount.FRACTION() / 10 ** (i+1)))
+            fraction += int(int(digit) * (Amount._fraction() / 10 ** (i+1)))
         return cls(parsed.group(1), value, fraction)
 
     # Comare two amounts, return:
@@ -75,16 +78,16 @@ class Amount:
     # 0 if a == b
     # 1 if a > b
     @staticmethod
-    def cmp(a, b):
-        if a.currency != b.currency:
-            raise CurrencyMismatch()
-        if a.value == b.value:
-            if a.fraction < b.fraction:
+    def cmp(am1, am2):
+        if am1.currency != am2.currency:
+            raise CurrencyMismatch(am1.currency, am2.currency)
+        if am1.value == am2.value:
+            if am1.fraction < am2.fraction:
                 return -1
-            if a.fraction > b.fraction:
+            if am1.fraction > am2.fraction:
                 return 1
             return 0
-        if a.value < b.value:
+        if am1.value < am2.value:
             return -1
         return 1
 
@@ -94,34 +97,35 @@ class Amount:
         self.fraction = fraction
 
     # Add the given amount to this one
-    def add(self, a):
-        if self.currency != a.currency:
-            raise CurrencyMismatch()
-        self.value += a.value
-        self.fraction += a.fraction
+    def add(self, amount):
+        if self.currency != amount.currency:
+            raise CurrencyMismatch(self.currency, amount.currency)
+        self.value += amount.value
+        self.fraction += amount.fraction
         self.__normalize()
 
     # Subtract passed amount from this one
-    def subtract(self, a):
-        if self.currency != a.currency:
-            raise CurrencyMismatch()
-        if self.fraction < a.fraction:
-            self.fraction += Amount.FRACTION()
+    def subtract(self, amount):
+        if self.currency != amount.currency:
+            raise CurrencyMismatch(self.currency, amount.currency)
+        if self.fraction < amount.fraction:
+            self.fraction += Amount._fraction()
             self.value -= 1
-        if self.value < a.value:
+        if self.value < amount.value:
             raise ValueError('self is lesser than amount to be subtracted')
-        self.value -= a.value
-        self.fraction -= a.fraction
+        self.value -= amount.value
+        self.fraction -= amount.fraction
 
     # Dump string from this amount, will put 'ndigits' numbers
     # after the dot.
     def stringify(self, ndigits):
         assert ndigits > 0
         ret = '%s:%s.' % (self.currency, str(self.value))
-        f = self.fraction
-        for i in range(0, ndigits):
-            ret += str(int(f / (Amount.FRACTION() / 10)))
-            f = (f * 10) % (Amount.FRACTION())
+        fraction = self.fraction
+        while ndigits > 0:
+            ret += str(int(fraction / (Amount._fraction() / 10)))
+            fraction = (fraction * 10) % (Amount._fraction())
+            ndigits -= 1
         return ret
 
     # Dump the Taler-compliant 'dict' amount