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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def sum_biomass_weight(reaction):
 """ Compute the sum of all reaction compounds. This function expects all metabolites of the biomass reaction to have formula information assigned. Parameters reaction : cobra.core.reaction.Reaction The biomass reaction of the model under investigation. Returns ------- float The molecular weight of the biomass reaction in units of g/mmol. """

    return sum(-coef * met.formula_weight
               for (met, coef) in iteritems(reaction.metabolites)) / 1000.0