Added check for order in _ok_for_muldiv. Clean up. Improved doc strings.

3 files changed, 41 insertions, 20 deletions

diff --git a/pint/quantity.py b/pint/quantity.py
index 0cdb4c5..35c864c 100644
--- a/pint/quantity.py
+++ b/pint/quantity.py
@@ -56,30 +56,34 @@ def _check(q1, other):
     return False
 
 
-def _only_multiplicative_units(q):
-    """Check if the quantity has non-multiplicative units.
+def _is_multiplicative(q):  # renamed from _only_multiplicative_units
+    """Check if the Quantity object has only multiplicative units.
     """
+    # XXX Turn this into a method/property of _Quantity?
     return not _get_non_multiplicative_units(q)
 
 
 def _get_non_multiplicative_units(q):
-    """Check if the quantity has a unit with non-zero offset
+    """Return a list of the of non-multiplicative units of the Quantity object
     """
+    # XXX Turn this into a method/property of _Quantity?
     offset_units = [unit for unit in q.units.keys()
                     if not q._REGISTRY._units[unit].is_multiplicative]
     return offset_units
 
 
 def _get_delta_units(q):
-    """Check if the quantity has a delta_unit
+    """Return list of delta units ot the Quantity object
     """
+    # XXX Turn this into a method/property of _Quantity? a class mathod?
     delta_units = [u for u in q.units.keys() if u.startswith("delta_")]
     return delta_units
 
 
 def _has_compatible_delta(q, unit):
-    """"Check if quantity has a delta_unit that is compatible with unit
+    """"Check if Quantity object has a delta_unit that is compatible with unit
     """
+    # XXX Turn this into a method/property of _Quantity?
     deltas = _get_delta_units(q)
     if 'delta_' + unit in deltas:
         return True
@@ -92,11 +96,12 @@ def _has_compatible_delta(q, unit):
 
 
 def _ok_for_muldiv(q, no_offset_units=None):
-    """Checks if quantity q can be multiplied with or divided
+    """Checks if Quantity object can be multiplied or divided
 
     :q: quantity object that is checked
     :no_offset_units: number of offset units in q
     """
+    # XXX Turn this into a method/property of _Quantity?
     is_ok = True
     if no_offset_units is None:
         no_offset_units = len(_get_non_multiplicative_units(q))
@@ -108,7 +113,9 @@ def _ok_for_muldiv(q, no_offset_units=None):
         if (len(q.units) == 1
                 and not q._REGISTRY.autoconvert_offset_to_baseunit):
             is_ok = False
-        # XXX check also for order?
+        if (q.units[0] != 1
+                and not q._REGISTRY.autoconvert_offset_to_baseunit):
+            is_ok = False
     return is_ok
 
 
@@ -665,6 +672,13 @@ class _Quantity(object):
             other_magnitude = _to_magnitude(other, self.force_ndarray)
         except TypeError:
             return NotImplemented
+
+        no_offset_units_self = len(_get_non_multiplicative_units(self))
+        if not _ok_for_muldiv(self, no_offset_units_self):
+            raise OffsetUnitCalculusError(self.units, '')
+        elif no_offset_units_self == 1 and len(self.units) == 1:
+            self = self.to_base_units()
+
         return self.__class__(other_magnitude / self._magnitude, 1 / self._units)
 
     def __rfloordiv__(self, other):
@@ -672,6 +686,13 @@ class _Quantity(object):
             other_magnitude = _to_magnitude(other, self.force_ndarray)
         except TypeError:
             return NotImplemented
+
+        no_offset_units_self = len(_get_non_multiplicative_units(self))
+        if not _ok_for_muldiv(self, no_offset_units_self):
+            raise OffsetUnitCalculusError(self.units, '')
+        elif no_offset_units_self == 1 and len(self.units) == 1:
+            self = self.to_base_units()
+
         return self.__class__(other_magnitude // self._magnitude, 1 / self._units)
 
     __div__ = __truediv__
@@ -687,7 +708,7 @@ class _Quantity(object):
         except TypeError:
             return NotImplemented
         else:
-            if not _only_multiplicative_units(self):
+            if not _is_multiplicative(self):
                 self.ito_base_units()
             self._magnitude **= _to_magnitude(other, self.force_ndarray)
             self._units **= other
@@ -700,7 +721,7 @@ class _Quantity(object):
             return NotImplemented
         else:
             new_self = self
-            if not _only_multiplicative_units(self):
+            if not _is_multiplicative(self):
                 new_self = self.to_base_units()
 
             magnitude = new_self._magnitude ** _to_magnitude(other, self.force_ndarray)
diff --git a/pint/testsuite/test_unit.py b/pint/testsuite/test_unit.py
index 9228f59..c0f4602 100644
--- a/pint/testsuite/test_unit.py
+++ b/pint/testsuite/test_unit.py
@@ -595,7 +595,6 @@ class TestErrors(BaseTestCase):
 
 class TestConvertWithOffset(QuantityTestCase, ParameterizedTestCase):
 
-
     # The dicts in convert_with_offset are used to create a UnitsContainer.
     # We create UnitsContainer to avoid any auto-conversion of units.
     convert_with_offset = [
diff --git a/pint/unit.py b/pint/unit.py
index a699947..77523e5 100644
--- a/pint/unit.py
+++ b/pint/unit.py
@@ -118,7 +118,8 @@ class OffsetUnitCalculusError(ValueError):
         self.extra_msg = extra_msg
 
     def __str__(self):
-        msg = ("Ambiguous operation with offset unit ('{0}', '{1}')."
+        msg = ("Ambiguous operation with offset unit (%s)." %
+               ', '.join(['%s' % u for u in [self.units1, self.units2] if u])
                + self.extra_msg)
         return msg.format(self.units1, self.units2)
 
@@ -467,8 +468,8 @@ class UnitRegistry(object):
     :type on_redefintion: str
     """
 
-    def __init__(self, filename='', force_ndarray=False, default_as_delta=True, 
-                 autoconvert_offset_to_baseunit=False, 
+    def __init__(self, filename='', force_ndarray=False, default_as_delta=True,
+                 autoconvert_offset_to_baseunit=False,
                  on_redefinition='warn'):
         self.Quantity = build_quantity_class(self, force_ndarray)
         self.Measurement = build_measurement_class(self, force_ndarray)
@@ -511,11 +512,11 @@ class UnitRegistry(object):
         #: When performing a multiplication of units, interpret
         #: non-multiplicative units as their *delta* counterparts.
         self.default_as_delta = default_as_delta
-        
-        # Determines if quantities with offset units are converted to their 
+
+        # Determines if quantities with offset units are converted to their
         # base units on multiplication and division.
         self.autoconvert_offset_to_baseunit = autoconvert_offset_to_baseunit
-        
+
         if filename == '':
             self.load_definitions('default_en.txt', True)
         elif filename is not None:
@@ -1034,7 +1035,7 @@ class UnitRegistry(object):
                 raise DimensionalityError(
                     src, dst, src_dim, dst_dim,
                     extra_msg=' - more than one offset unit.')
-                    
+
             # validate that offset unit is not used in multiplicative context
             if ((len(src_offset_units) == 1 and len(src) > 1)
                     or (len(dst_offset_units) == 1 and len(dst) > 1)
@@ -1042,7 +1043,7 @@ class UnitRegistry(object):
                 raise DimensionalityError(
                     src, dst, src_dim, dst_dim,
                     extra_msg=' - offset unit used in multiplicative context.')
-                    
+
             # Validate that order of offset unit is not above one.
             if src_offset_units:
                 if src_offset_units[0][1] > 1:
@@ -1171,7 +1172,7 @@ class UnitRegistry(object):
             cname = self.get_name(name)
             if not cname:
                 continue
-            if as_delta and (many or (not many and abs(value) != 1)):
+            if as_delta and (many or (not many and value != 1)):
                 definition = self._units[cname]
                 if not definition.is_multiplicative:
                     cname = 'delta_' + cname
@@ -1195,7 +1196,7 @@ class UnitRegistry(object):
         unknown = set()
         for toknum, tokval, _, _, _ in gen:
             if toknum == NAME:
-                # TODO: Integrate math better, Replace eval
+                # TODO: Integrate math better, Replace eval, make as_delta-aware
                 if tokval == 'pi' or tokval in values:
                     result.append((toknum, tokval))
                     continue