code: async def enumerate(source, start=0, step=1):
      
      count = itertools.count(start, step)
      async with streamcontext(source) as streamer:
          async for item in streamer:
              yield next(count), item
docs: Generate ``(index, value)`` tuples from an asynchronous sequence.
  
      This index is computed using a starting point and an increment,
      respectively defaulting to ``0`` and ``1``.