docs: def _exec(self, binary, stdin='', args=(), env={}):
          """
          Executes the binary using stdin and args with environment
          variables.
  
          Returns a tuple of stdout, stderr.  Format determined by the
          input text (either str or bytes), and the encoding of str will
          be determined by the locale this module was imported in.
          """
  
          call_kw = self._gen_call_kws(**env)
          call_args = [self._get_exec_binary(call_kw)]
          call_args.extend(args)
          return fork_exec(call_args, stdin, **call_kw)