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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 hsts_header(self):
 """Returns the proper HSTS policy."""

        hsts_policy = 'max-age={0}'.format(self.hsts_age)

        if self.hsts_include_subdomains:
            hsts_policy += '; includeSubDomains'

        return hsts_policy