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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_post_policy(self, expiration_time, conditions):
 """ Taken from the AWS book Python examples and modified for use with boto """

        assert type(expiration_time) == time.struct_time, \
            'Policy document must include a valid expiration Time object'

        # Convert conditions object mappings to condition statements

        return '{"expiration": "%s",\n"conditions": [%s]}' % \
            (time.strftime(boto.utils.ISO8601, expiration_time), ",".join(conditions))