code: def get_sign_command(self, filename, signer, sign_password,
                           keystore=None):
          
          cmd = [self.gpg, '--status-fd', '2', '--no-tty']
          if keystore is None:
              keystore = self.gpg_home
          if keystore:
              cmd.extend(['--homedir', keystore])
          if sign_password is not None:
              cmd.extend(['--batch', '--passphrase-fd', '0'])
          td = tempfile.mkdtemp()
          sf = os.path.join(td, os.path.basename(filename) + '.asc')
          cmd.extend(['--detach-sign', '--armor', '--local-user',
                      signer, '--output', sf, filename])
          logger.debug('invoking: %s', ' '.join(cmd))
          return cmd, sf
docs: Return a suitable command for signing a file.
  
          :param filename: The pathname to the file to be signed.
          :param signer: The identifier of the signer of the file.
          :param sign_password: The passphrase for the signer's
                                private key used for signing.
          :param keystore: The path to a directory which contains the keys
                           used in verification. If not specified, the
                           instance's ``gpg_home`` attribute is used instead.
          :return: The signing command as a list suitable to be
                   passed to :class:`subprocess.Popen`.