Show More
@@ -1,186 +1,185 b'' | |||
|
1 | ||
|
2 | .. autoawait: | |
|
1 | .. _autoawait: | |
|
3 | 2 | |
|
4 | 3 | Asynchronous in REPL: Autoawait |
|
5 | 4 | =============================== |
|
6 | 5 | |
|
7 | 6 | Starting with IPython 6.0, and when user Python 3.6 and above, IPython offer the |
|
8 | 7 | ability to run asynchronous code from the REPL. constructs which are |
|
9 | 8 | :exc:`SyntaxError` s in the Python REPL can be used seamlessly in IPython. |
|
10 | 9 | |
|
11 | 10 | When a supported libray is used, IPython will automatically `await` Futures |
|
12 | 11 | and Coroutines in the REPL. This will happen if an :ref:`await <await>` (or `async`) is |
|
13 | 12 | use at top level scope, or if any structure valid only in `async def |
|
14 | 13 | <https://docs.python.org/3/reference/compound_stmts.html#async-def>`_ function |
|
15 | 14 | context are present. For example, the following being a syntax error in the |
|
16 | 15 | Python REPL:: |
|
17 | 16 | |
|
18 | 17 | Python 3.6.0 |
|
19 | 18 | [GCC 4.2.1] |
|
20 | 19 | Type "help", "copyright", "credits" or "license" for more information. |
|
21 | 20 | >>> import aiohttp |
|
22 | 21 | >>> result = aiohttp.get('https://api.github.com') |
|
23 | 22 | >>> response = await result |
|
24 | 23 | File "<stdin>", line 1 |
|
25 | 24 | response = await result |
|
26 | 25 | ^ |
|
27 | 26 | SyntaxError: invalid syntax |
|
28 | 27 | |
|
29 | 28 | Should behave as expected in the IPython REPL:: |
|
30 | 29 | |
|
31 | 30 | Python 3.6.0 |
|
32 | 31 | Type 'copyright', 'credits' or 'license' for more information |
|
33 | 32 | IPython 6.0.0.dev -- An enhanced Interactive Python. Type '?' for help. |
|
34 | 33 | |
|
35 | 34 | In [1]: import aiohttp |
|
36 | 35 | ...: result = aiohttp.get('https://api.github.com') |
|
37 | 36 | |
|
38 | 37 | In [2]: response = await result |
|
39 | 38 | <pause for a few 100s ms> |
|
40 | 39 | |
|
41 | 40 | In [3]: await response.json() |
|
42 | 41 | Out[3]: |
|
43 | 42 | {'authorizations_url': 'https://api.github.com/authorizations', |
|
44 | 43 | 'code_search_url': 'https://api.github.com/search/code?q={query}...', |
|
45 | 44 | ... |
|
46 | 45 | } |
|
47 | 46 | |
|
48 | 47 | |
|
49 | 48 | You can use the ``c.InteractiveShell.autoawait`` configuration option and set it |
|
50 | 49 | to :any:`False` to deactivate automatic wrapping of asynchronous code. You can also |
|
51 | 50 | use the :magic:`%autoawait` magic to toggle the behavior at runtime:: |
|
52 | 51 | |
|
53 | 52 | In [1]: %autoawait False |
|
54 | 53 | |
|
55 | 54 | In [2]: %autoawait |
|
56 | 55 | IPython autoawait is `Off`, and set to use `IPython.core.interactiveshell._asyncio_runner` |
|
57 | 56 | |
|
58 | 57 | |
|
59 | 58 | |
|
60 | 59 | By default IPython will assume integration with Python's provided |
|
61 | 60 | :mod:`asyncio`, but integration with other libraries is provided. In particular |
|
62 | 61 | we provide experimental integration with the ``curio`` and ``trio`` library. |
|
63 | 62 | |
|
64 | 63 | You can switch current integration by using the |
|
65 | 64 | ``c.InteractiveShell.loop_runner`` option or the ``autoawait <name |
|
66 | 65 | integration>`` magic. |
|
67 | 66 | |
|
68 | 67 | For example:: |
|
69 | 68 | |
|
70 | 69 | In [1]: %autoawait trio |
|
71 | 70 | |
|
72 | 71 | In [2]: import trio |
|
73 | 72 | |
|
74 | 73 | In [3]: async def child(i): |
|
75 | 74 | ...: print(" child %s goes to sleep"%i) |
|
76 | 75 | ...: await trio.sleep(2) |
|
77 | 76 | ...: print(" child %s wakes up"%i) |
|
78 | 77 | |
|
79 | 78 | In [4]: print('parent start') |
|
80 | 79 | ...: async with trio.open_nursery() as n: |
|
81 | 80 | ...: for i in range(5): |
|
82 | 81 | ...: n.spawn(child, i) |
|
83 | 82 | ...: print('parent end') |
|
84 | 83 | parent start |
|
85 | 84 | child 2 goes to sleep |
|
86 | 85 | child 0 goes to sleep |
|
87 | 86 | child 3 goes to sleep |
|
88 | 87 | child 1 goes to sleep |
|
89 | 88 | child 4 goes to sleep |
|
90 | 89 | <about 2 seconds pause> |
|
91 | 90 | child 2 wakes up |
|
92 | 91 | child 1 wakes up |
|
93 | 92 | child 0 wakes up |
|
94 | 93 | child 3 wakes up |
|
95 | 94 | child 4 wakes up |
|
96 | 95 | parent end |
|
97 | 96 | |
|
98 | 97 | |
|
99 | 98 | In the above example, ``async with`` at top level scope is a syntax error in |
|
100 | 99 | Python. |
|
101 | 100 | |
|
102 | 101 | Using this mode can have unexpected consequences if used in interaction with |
|
103 | 102 | other features of IPython and various registered extensions. In particular if you |
|
104 | 103 | are a direct or indirect user of the AST transformers, these may not apply to |
|
105 | 104 | your code. |
|
106 | 105 | |
|
107 | 106 | The default loop, or runner does not run in the background, so top level |
|
108 | 107 | asynchronous code must finish for the REPL to allow you to enter more code. As |
|
109 | 108 | with usual Python semantic, the awaitables are started only when awaited for the |
|
110 | 109 | first time. That is to say, in first example, no network request is done between |
|
111 | 110 | ``In[1]`` and ``In[2]``. |
|
112 | 111 | |
|
113 | 112 | |
|
114 | 113 | Internals |
|
115 | 114 | ========= |
|
116 | 115 | |
|
117 | 116 | As running asynchronous code is not supported in interactive REPL as of Python |
|
118 | 117 | 3.6 we have to rely to a number of complex workaround to allow this to happen. |
|
119 | 118 | It is interesting to understand how this works in order to understand potential |
|
120 | 119 | bugs, or provide a custom runner. |
|
121 | 120 | |
|
122 | 121 | Among the many approaches that are at our disposition, we find only one that |
|
123 | 122 | suited out need. Under the hood we :ct the code object from a async-def function |
|
124 | 123 | and run it in global namesapace after modifying the ``__code__`` object.:: |
|
125 | 124 | |
|
126 | 125 | async def inner_async(): |
|
127 | 126 | locals().update(**global_namespace) |
|
128 | 127 | # |
|
129 | 128 | # here is user code |
|
130 | 129 | # |
|
131 | 130 | return last_user_statement |
|
132 | 131 | codeobj = modify(inner_async.__code__) |
|
133 | 132 | coroutine = eval(codeobj, user_ns) |
|
134 | 133 | display(loop_runner(coroutine)) |
|
135 | 134 | |
|
136 | 135 | |
|
137 | 136 | |
|
138 | 137 | The first thing you'll notice is that unlike classical ``exec``, there is only |
|
139 | 138 | one name space. Second, user code runs in a function scope, and not a module |
|
140 | 139 | scope. |
|
141 | 140 | |
|
142 | 141 | On top of the above there are significant modification to the AST of |
|
143 | 142 | ``function``, and ``loop_runner`` can be arbitrary complex. So there is a |
|
144 | 143 | significant overhead to this kind of code. |
|
145 | 144 | |
|
146 | 145 | By default the generated coroutine function will be consumed by Asyncio's |
|
147 | 146 | ``loop_runner = asyncio.get_evenloop().run_until_complete()`` method. It is |
|
148 | 147 | though possible to provide your own. |
|
149 | 148 | |
|
150 | 149 | A loop runner is a *synchronous* function responsible from running a coroutine |
|
151 | 150 | object. |
|
152 | 151 | |
|
153 | 152 | The runner is responsible from ensuring that ``coroutine`` run to completion, |
|
154 | 153 | and should return the result of executing the coroutine. Let's write a |
|
155 | 154 | runner for ``trio`` that print a message when used as an exercise, ``trio`` is |
|
156 | 155 | special as it usually prefer to run a function object and make a coroutine by |
|
157 | 156 | itself, we can get around this limitation by wrapping it in an async-def without |
|
158 | 157 | parameters and passing this value to ``trio``:: |
|
159 | 158 | |
|
160 | 159 | |
|
161 | 160 | In [1]: import trio |
|
162 | 161 | ...: from types import CoroutineType |
|
163 | 162 | ...: |
|
164 | 163 | ...: def trio_runner(coro:CoroutineType): |
|
165 | 164 | ...: print('running asynchronous code') |
|
166 | 165 | ...: async def corowrap(coro): |
|
167 | 166 | ...: return await coro |
|
168 | 167 | ...: return trio.run(corowrap, coro) |
|
169 | 168 | |
|
170 | 169 | We can set it up by passing it to ``%autoawait``:: |
|
171 | 170 | |
|
172 | 171 | In [2]: %autoawait trio_runner |
|
173 | 172 | |
|
174 | 173 | In [3]: async def async_hello(name): |
|
175 | 174 | ...: await trio.sleep(1) |
|
176 | 175 | ...: print(f'Hello {name} world !') |
|
177 | 176 | ...: await trio.sleep(1) |
|
178 | 177 | |
|
179 | 178 | In [4]: await async_hello('async') |
|
180 | 179 | running asynchronous code |
|
181 | 180 | Hello async world ! |
|
182 | 181 | |
|
183 | 182 | |
|
184 | 183 | Asynchronous programming in python (and in particular in the REPL) is still a |
|
185 | 184 | relatively young subject. Feel free to contribute improvements to this codebase |
|
186 | 185 | and give us feedback. |
General Comments 0
You need to be logged in to leave comments.
Login now