fix for cmp and add, sub

bia/test_units.py

@@ -30,9 +30,14 @@ def test_basic_cmp():
 
 def test_conversion_cmp():
     assert Mass(1, 'kg') < Mass(100, 'lb')
-    assert Mass(10000000, 'g') > Mass(100, 'lb')
+    assert Mass(1000000, 'g') > Mass(100, 'lb')
 
 
-def test_add_sub():
+def test_addition():
     assert Mass(1, 'kg') + Mass(2, 'kg') == Mass(3, 'kg')
+    assert Mass(1, 'kg') + Mass(1, 'lb') > Mass(1.4, 'kg')
+
+
+def test_subtraction():
     assert Mass(2, 'kg') - Mass(1, 'kg') == Mass(1, 'kg')
+    assert Mass(1, 'kg') - Mass(1, 'lb') < Mass(0.55, 'kg')

bia/units.py

@@ -13,7 +13,7 @@ class Unit(object):
     _mapping = {}
 
     def __init__(self, n, unit):
-        self.scalar = n
+        self.scalar = float(n)
         if unit not in self._mapping:
             raise ValueError('invalid unit {} for {}'.format(unit, self.__class__.__name__))
         self.unit = unit
@@ -41,7 +41,8 @@ class Unit(object):
     def __cmp__(self, other):
         if self.unit != other.unit:
             other = other.as_unit(self.unit)
-        return self.scalar - other.scalar
+        # cmp() removed in Python 3, recommended to replace with this
+        return (self.scalar > other.scalar) - (self.scalar < other.scalar)
 
     def __add__(self, other):
         if self.unit != other.unit: