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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 build_static(self):
 """ Build static files """

        if not os.path.isdir(self.build_static_dir):
            os.makedirs(self.build_static_dir)
        copy_tree(self.static_dir, self.build_static_dir)
        if self.webassets_cmd:
            self.webassets_cmd.build()