code: def constant(value, delay=None):
      
      @asyncio.coroutine
      def coro():
          if delay:
              yield from asyncio.sleep(delay)
          return value
  
      return coro
docs: Returns a coroutine function that when called, always returns
      the provided value.
  
      This function has an alias: `paco.identity`.
  
      Arguments:
          value (mixed): value to constantly return when coroutine is called.
          delay (int/float): optional return value delay in seconds.
  
      Returns:
          coroutinefunction
  
      Usage::
  
          coro = paco.constant('foo')
  
          await coro()
          # => 'foo'
          await coro()
          # => 'foo'