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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 update_available(self, name):
 """Updates the "available" metric for the given quota."""

        quota = self.usages.get(name, {}).get('quota', float('inf'))
        available = quota - self.usages[name]['used']
        if available < 0:
            available = 0
        self.usages[name]['available'] = available