code: def set_header(self, name, value, append=False):
          ''' Create a new response header, replacing any previously defined
              headers with the same name. '''
          if append:
              self.add_header(name, value)
          else:
              self._headers[_hkey(name)] = [str(value)f set_header(self, name, value, append=False):
          ''' Create a new response header, replacing any previously defined
              headers with the same name. '''
          if append:
              self.add_header(name, value)
          else:
              self._headers[_hkey(name)] = [str(value)]
docs: Create a new response header, replacing any previously defined
              headers with the same name.