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docs/source/interactive/autoawait.rst

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-.. autoawait:
+.. _autoawait:
 
 Asynchronous in REPL: Autoawait
 ===============================
 
 Starting with IPython 6.0, and when user Python 3.6 and above, IPython offer the
 ability to run asynchronous code from the REPL. constructs which are
 :exc:`SyntaxError` s in the Python REPL can be used seamlessly in IPython.
 
 When a supported libray is used, IPython will automatically `await` Futures
 and Coroutines in the REPL. This will happen if an :ref:`await <await>` (or `async`) is
 use at top level scope, or if any structure valid only in `async def
 <https://docs.python.org/3/reference/compound_stmts.html#async-def>`_ function
 context are present. For example, the following being a syntax error in the
 Python REPL::
 
     Python 3.6.0 
     [GCC 4.2.1]
     Type "help", "copyright", "credits" or "license" for more information.
     >>> import aiohttp
     >>> result = aiohttp.get('https://api.github.com')
     >>> response = await result
       File "<stdin>", line 1
         response = await result
                               ^
     SyntaxError: invalid syntax
 
 Should behave as expected in the IPython REPL::
 
     Python 3.6.0
     Type 'copyright', 'credits' or 'license' for more information
     IPython 6.0.0.dev -- 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}...',
     ...
     }
 
 
 You can use the ``c.InteractiveShell.autoawait`` configuration option and set it
 to :any:`False` to deactivate automatic wrapping of asynchronous code. You can also
 use the :magic:`%autoawait` magic to toggle the behavior at runtime::
 
     In [1]: %autoawait False
 
     In [2]: %autoawait
     IPython autoawait is `Off`, and set to use `IPython.core.interactiveshell._asyncio_runner`
 
 
 
 By default IPython will assume integration with Python's provided
 :mod:`asyncio`, but integration with other libraries is provided. In particular
 we provide experimental integration with the ``curio`` and ``trio`` library.
 
 You can switch current integration by using the
 ``c.InteractiveShell.loop_runner`` option or the ``autoawait <name
 integration>`` magic.
 
 For example::
 
     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(5):
        ...:         n.spawn(child, i)
        ...: print('parent end')
     parent start
        child 2 goes to sleep
        child 0 goes to sleep
        child 3 goes to sleep
        child 1 goes to sleep
        child 4 goes to sleep
        <about 2 seconds pause>
        child 2 wakes up
        child 1 wakes up
        child 0 wakes up
        child 3 wakes up
        child 4 wakes up
     parent end
 
 
 In the above example, ``async with`` at top level scope is a syntax error in
 Python.
 
 Using this mode can have unexpected consequences if used in interaction with
 other features of IPython and various registered extensions. In particular if you
 are a direct or indirect user of the AST transformers, these may not apply to
 your code.
 
 The default loop, or runner does not run in the background, so top level
 asynchronous code must finish for the REPL to allow you to enter more code. As
 with usual Python semantic, the awaitables are started only when awaited for the
 first time. That is to say, in first example, no network request is done between
 ``In[1]`` and ``In[2]``.
 
 
 Internals
 =========
 
 As running asynchronous code is not supported in interactive REPL as of Python
 3.6 we have to rely to a number of complex workaround to allow this to happen.
 It is interesting to understand how this works in order to understand potential
 bugs, or provide a custom runner.
 
 Among the many approaches that are at our disposition, we find only one that
 suited out need. Under the hood we :ct the code object from a async-def function
 and run it in global namesapace after modifying the ``__code__`` object.::
 
     async def inner_async():
         locals().update(**global_namespace)
         #
         # here is user code
         #
         return last_user_statement
     codeobj = modify(inner_async.__code__)
     coroutine = eval(codeobj, user_ns)
     display(loop_runner(coroutine))
 
 
 
 The first thing you'll notice is that unlike classical ``exec``, there is only
 one name space. Second, user code runs in a function scope, and not a module
 scope.
 
 On top of the above there are significant modification to the AST of
 ``function``, and ``loop_runner`` can be arbitrary complex. So there is a
 significant overhead to this kind of code.
 
 By default the generated coroutine function will be consumed by Asyncio's
 ``loop_runner = asyncio.get_evenloop().run_until_complete()`` method. It is
 though possible to provide your own.
 
 A loop runner is a *synchronous*  function responsible from running a coroutine
 object.
 
 The runner is responsible from ensuring that ``coroutine`` run to completion,
 and should return the result of executing the coroutine. Let's write a
 runner for ``trio`` that print a message when used as an exercise, ``trio`` is
 special as it usually prefer to run a function object and make a coroutine by
 itself, we can get around this limitation by wrapping it in an async-def without
 parameters and passing this value to ``trio``::
 
 
     In [1]: import trio
        ...: from types import CoroutineType
        ...:
        ...: def trio_runner(coro:CoroutineType):
        ...:     print('running asynchronous code')
        ...:     async def corowrap(coro):
        ...:         return await coro
        ...:     return trio.run(corowrap, coro)
 
 We can set it up by passing it to ``%autoawait``::
 
     In [2]: %autoawait trio_runner
 
     In [3]: async def async_hello(name):
        ...:     await trio.sleep(1)
        ...:     print(f'Hello {name} world !')
        ...:     await trio.sleep(1)
 
     In [4]: await async_hello('async')
     running asynchronous code
     Hello async world !
 
 
 Asynchronous programming in python (and in particular in the REPL) is still a
 relatively young subject. Feel free to contribute improvements to this codebase
 and give us feedback.