Autowait: Asynchronous REPL

Staring with IPython 7.0 and on Python 3.6+, IPython can automatically await code at top level, you should not need to access an event loop or runner yourself. To know more read the :ref:`autoawait` section of our docs, see :ghpull:`11265` or try the following code:

Python 3.6.0
Type 'copyright', 'credits' or 'license' for more information
IPython 7.0.0 -- An enhanced Interactive Python. Type '?' for help.

In [1]: import aiohttp
   ...: result = aiohttp.get('https://api.github.com')

In [2]: response = await result
<pause for a few 100s ms>

In [3]: await response.json()
Out[3]:
{'authorizations_url': 'https://api.github.com/authorizations',
 'code_search_url': 'https://api.github.com/search/code?q={query}{&page,per_page,sort,order}',
...
}

Integration is by default with asyncio, but other libraries can be configured, like curio or trio, to improve concurrency in the REPL:

In [1]: %autoawait trio

In [2]: import trio

In [3]: async def child(i):
   ...:     print("   child %s goes to sleep"%i)
   ...:     await trio.sleep(2)
   ...:     print("   child %s wakes up"%i)

In [4]: print('parent start')
   ...: async with trio.open_nursery() as n:
   ...:     for i in range(3):
   ...:         n.spawn(child, i)
   ...: print('parent end')
parent start
   child 2 goes to sleep
   child 0 goes to sleep
   child 1 goes to sleep
   <about 2 seconds pause>
   child 2 wakes up
   child 1 wakes up
   child 0 wakes up
parent end

See :ref:`autoawait` for more information.

Asynchronous code in a Notebook interface or any other frontend using the Jupyter Protocol will need further updates of the IPykernel package.

Non-Asynchronous code

As the internal API of IPython are now asynchronous, IPython need to run under an even loop. In order to allow many workflow, (like using the %run magic, or copy_pasting code that explicitly starts/stop event loop), when top-level code is detected as not being asynchronous, IPython code is advanced via a pseudo-synchronous runner, and will not may not advance pending tasks.

Change to Nested Embed

The introduction of the ability to run async code had some effect on the IPython.embed() API. By default embed will not allow you to run asynchronous code unless a event loop is specified.

Expected Future changes

We expect more internal but public IPython function to become async, and will likely end up having a persisting event loop while IPython is running.

Thanks

This took more than a year in the making, and the code was rebased a number of time leading to commit authorship that may have been lost in the final Pull-Request. Huge thanks to many people for contribution, discussion, code, documentation, use-case: dalejung, danielballan, ellisonbg, fperez, gnestor, minrk, njsmith, pganssle, tacaswell, takluyver , vidartf ... And many other.