The right of private defence in no case extends to the inflicting of more harm than it is necessary to inflict for the purpose of defence. Explanation 1.-A person is not deprived of the right of private defence against an act done, or attempted to be done, by a public servant, as such unless he knows, or has reason to believe, that the person doing the act is such public servant. Explanation 2.-A person is not deprived of the right of private defence against an act done, or attempted to be done, by the direction of a public servant, unless he knows, or has reason to believe, that the person doing the act is acting by such direction, or unless such person states the authority under which he acts, or if he has authority in writing, unless he produces such authority, if demanded.