def for_amount(self, to_quantity, to_unit):
"""Return a `FoodNutritionInfo` for the given quantity and unit.
"""
# If units are the same, scale by quantity alone
if self.unit == to_unit:
factor = float(to_quantity) / self.quantity
else:
# Scaling factor for a 1-gram serving size
gram_serving = 1.0 / (helpers.to_grams(self.unit, self.food) * self.quantity)
# Target quantity in grams
target_grams = helpers.to_grams(to_unit, self.food) * to_quantity
# Overall scaling factor to apply to all nutritional info
factor = gram_serving * target_grams
return FoodNutritionInfo(
food = self.food,
quantity = to_quantity,
unit = to_unit,
calories = factor * self.calories,
fat_calories = factor * self.fat_calories,
fat = factor * self.fat,
carb = factor * self.carb,
sodium = factor * self.sodium,
protein = factor * self.protein,
cholesterol = factor * self.cholesterol
)
def test_convert_weight_to_grams(self):
"""Convert units of weight to grams.
"""
pound = Unit.objects.get(name='pound')
grams_per_pound = convert_unit('pound', 'gram')
self.failUnlessEqual(to_grams(pound), grams_per_pound)
kilo = Unit.objects.get(name='kilogram')
grams_per_kilo = convert_unit('kilogram', 'gram')
self.failUnlessEqual(to_grams(kilo), grams_per_kilo)
def test_convert_volume_to_grams(self):
"""Convert units of volume to grams.
"""
# Two foods with very different densities
honey = Food.objects.get(name='honey')
paprika = Food.objects.get(name='paprika')
# Two units of volume
ml = Unit.objects.get(name='milliliter')
cup = Unit.objects.get(name='cup')
ml_per_cup = Equivalence.objects.get(unit=cup, to_unit=ml).to_quantity
# Convert units of volume into grams
# Without food, assume 1.0 g/ml
self.failUnlessEqual(to_grams(ml), 1.0)
self.failUnlessEqual(to_grams(cup), 1.0 * ml_per_cup)
# With food, use its density
self.failUnlessEqual(to_grams(ml, honey), honey.grams_per_ml)
self.failUnlessEqual(to_grams(ml, paprika), paprika.grams_per_ml)
self.failUnlessEqual(to_grams(cup, honey), honey.grams_per_ml * ml_per_cup)
self.failUnlessEqual(to_grams(cup, paprika), paprika.grams_per_ml * ml_per_cup)