[Tutor] parsing chemical formula

[Steve Spicklemire]

I guess we're neglecting the mass defect due to the chemical
binding energy. 

;-)

How about something like:

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# I'm making these up.... I really don't know the correct masses off the top...
#

ElementDict = {'H':1.0, 'He':4.0, 'Li':6.0, 'O':16.0 }  # and on and on  .....

class ElementContainer:

    def __init__(self, name, count):
	self.name = name
	self.count = count


class Molecule:
    
    elementList = None
    massDefect = None   # just in case we want to get fancy...

    def addElement(self, name, count):

	if self.elementList is None:
	    self.elementList = []    # a list allows multiple instances of ElementContainers
	                             # with the same element...

	self.elementList.append(ElementContainer(name, count))

    def calcWeight(self):
	weight = 0.0

	for element in self.elementList:
	    weight = weight + element.count*ElementDict[element.name]

	if self.massDefect is not None:
	    weight = weight - massDefect

	return weight


if __name__=='__main__':
    m = Molecule()

    m.addElement('H',2)
    m.addElement('O',1)

    print "This damp example has a result of: ", m.calcWeight()


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-steve