-
Notifications
You must be signed in to change notification settings - Fork 0
Expand file tree
/
Copy pathcontextvars.html
More file actions
479 lines (417 loc) · 31.5 KB
/
contextvars.html
File metadata and controls
479 lines (417 loc) · 31.5 KB
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="zh_TW">
<head>
<meta http-equiv="X-UA-Compatible" content="IE=Edge" />
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>18. contextvars — Context Variables — Python 3.7.0 說明文件</title>
<link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" />
<link rel="stylesheet" href="../_static/pygments.css" type="text/css" />
<script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script>
<script type="text/javascript" src="../_static/jquery.js"></script>
<script type="text/javascript" src="../_static/underscore.js"></script>
<script type="text/javascript" src="../_static/doctools.js"></script>
<script type="text/javascript" src="../_static/translations.js"></script>
<script type="text/javascript" src="../_static/sidebar.js"></script>
<link rel="search" type="application/opensearchdescription+xml"
title="在 Python 3.7.0 說明文件 中搜尋"
href="../_static/opensearch.xml"/>
<link rel="author" title="關於這些文件" href="../about.html" />
<link rel="index" title="索引" href="../genindex.html" />
<link rel="search" title="搜尋" href="../search.html" />
<link rel="copyright" title="Copyright" href="../copyright.html" />
<link rel="next" title="19. Interprocess Communication and Networking" href="ipc.html" />
<link rel="prev" title="17.10. dummy_threading — Drop-in replacement for the threading module" href="dummy_threading.html" />
<link rel="shortcut icon" type="image/png" href="../_static/py.png" />
<link rel="canonical" href="https://docs.python.org/3/library/contextvars.html" />
<script type="text/javascript" src="../_static/copybutton.js"></script>
<script type="text/javascript" src="../_static/switchers.js"></script>
</head><body>
<div class="related" role="navigation" aria-label="related navigation">
<h3>瀏覽</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="General Index"
accesskey="I">索引</a></li>
<li class="right" >
<a href="../py-modindex.html" title="Python 模組索引"
>模組</a> |</li>
<li class="right" >
<a href="ipc.html" title="19. Interprocess Communication and Networking"
accesskey="N">下一頁</a> |</li>
<li class="right" >
<a href="dummy_threading.html" title="17.10. dummy_threading — Drop-in replacement for the threading module"
accesskey="P">上一頁</a> |</li>
<li><img src="../_static/py.png" alt=""
style="vertical-align: middle; margin-top: -1px"/></li>
<li><a href="https://www.python.org/">Python</a> »</li>
<li>
<span class="language_switcher_placeholder">zh_TW</span>
<span class="version_switcher_placeholder">3.7.0</span>
<a href="../index.html">Documentation </a> »
</li>
<li class="nav-item nav-item-1"><a href="index.html" accesskey="U">Python 標準函式庫 (Standard Library)</a> »</li>
<li class="right">
<div class="inline-search" style="display: none" role="search">
<form class="inline-search" action="../search.html" method="get">
<input placeholder="Quick search" type="text" name="q" />
<input type="submit" value="Go" />
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
<script type="text/javascript">$('.inline-search').show(0);</script>
|
</li>
</ul>
</div>
<div class="document">
<div class="documentwrapper">
<div class="bodywrapper">
<div class="body" role="main">
<div class="section" id="module-contextvars">
<span id="contextvars-context-variables"></span><h1>18. <a class="reference internal" href="#module-contextvars" title="contextvars: Context Variables"><code class="xref py py-mod docutils literal notranslate"><span class="pre">contextvars</span></code></a> — Context Variables<a class="headerlink" href="#module-contextvars" title="本標題的永久連結">¶</a></h1>
<hr class="docutils" />
<p>This module provides APIs to manage, store, and access context-local
state. The <a class="reference internal" href="#contextvars.ContextVar" title="contextvars.ContextVar"><code class="xref py py-class docutils literal notranslate"><span class="pre">ContextVar</span></code></a> class is used to declare
and work with <em>Context Variables</em>. The <a class="reference internal" href="#contextvars.copy_context" title="contextvars.copy_context"><code class="xref py py-func docutils literal notranslate"><span class="pre">copy_context()</span></code></a>
function and the <a class="reference internal" href="#contextvars.Context" title="contextvars.Context"><code class="xref py py-class docutils literal notranslate"><span class="pre">Context</span></code></a> class should be used to
manage the current context in asynchronous frameworks.</p>
<p>Context managers that have state should use Context Variables
instead of <a class="reference internal" href="threading.html#threading.local" title="threading.local"><code class="xref py py-func docutils literal notranslate"><span class="pre">threading.local()</span></code></a> to prevent their state from
bleeding to other code unexpectedly, when used in concurrent code.</p>
<p>See also <span class="target" id="index-0"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0567"><strong>PEP 567</strong></a> for additional details.</p>
<div class="versionadded">
<p><span class="versionmodified">3.7 版新加入.</span></p>
</div>
<div class="section" id="context-variables">
<h2>18.1. Context Variables<a class="headerlink" href="#context-variables" title="本標題的永久連結">¶</a></h2>
<dl class="class">
<dt id="contextvars.ContextVar">
<em class="property">class </em><code class="descclassname">contextvars.</code><code class="descname">ContextVar</code><span class="sig-paren">(</span><em>name</em><span class="optional">[</span>, <em>*</em>, <em>default</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#contextvars.ContextVar" title="本定義的永久連結">¶</a></dt>
<dd><p>This class is used to declare a new Context Variable, e.g.:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">var</span><span class="p">:</span> <span class="n">ContextVar</span><span class="p">[</span><span class="nb">int</span><span class="p">]</span> <span class="o">=</span> <span class="n">ContextVar</span><span class="p">(</span><span class="s1">'var'</span><span class="p">,</span> <span class="n">default</span><span class="o">=</span><span class="mi">42</span><span class="p">)</span>
</pre></div>
</div>
<p>The required <em>name</em> parameter is used for introspection and debug
purposes.</p>
<p>The optional keyword-only <em>default</em> parameter is returned by
<a class="reference internal" href="#contextvars.ContextVar.get" title="contextvars.ContextVar.get"><code class="xref py py-meth docutils literal notranslate"><span class="pre">ContextVar.get()</span></code></a> when no value for the variable is found
in the current context.</p>
<p><strong>Important:</strong> Context Variables should be created at the top module
level and never in closures. <a class="reference internal" href="#contextvars.Context" title="contextvars.Context"><code class="xref py py-class docutils literal notranslate"><span class="pre">Context</span></code></a> objects hold strong
references to context variables which prevents context variables
from being properly garbage collected.</p>
<dl class="attribute">
<dt id="contextvars.ContextVar.name">
<code class="descname">name</code><a class="headerlink" href="#contextvars.ContextVar.name" title="本定義的永久連結">¶</a></dt>
<dd><p>The name of the variable. This is a read-only property.</p>
<div class="versionadded">
<p><span class="versionmodified">3.7.1 版新加入.</span></p>
</div>
</dd></dl>
<dl class="method">
<dt id="contextvars.ContextVar.get">
<code class="descname">get</code><span class="sig-paren">(</span><span class="optional">[</span><em>default</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#contextvars.ContextVar.get" title="本定義的永久連結">¶</a></dt>
<dd><p>Return a value for the context variable for the current context.</p>
<p>If there is no value for the variable in the current context,
the method will:</p>
<ul class="simple">
<li>return the value of the <em>default</em> argument of the method,
if provided; or</li>
<li>return the default value for the context variable,
if it was created with one; or</li>
<li>raise a <a class="reference internal" href="exceptions.html#LookupError" title="LookupError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">LookupError</span></code></a>.</li>
</ul>
</dd></dl>
<dl class="method">
<dt id="contextvars.ContextVar.set">
<code class="descname">set</code><span class="sig-paren">(</span><em>value</em><span class="sig-paren">)</span><a class="headerlink" href="#contextvars.ContextVar.set" title="本定義的永久連結">¶</a></dt>
<dd><p>Call to set a new value for the context variable in the current
context.</p>
<p>The required <em>value</em> argument is the new value for the context
variable.</p>
<p>Returns a <a class="reference internal" href="#contextvars.contextvars.Token" title="contextvars.contextvars.Token"><code class="xref py py-class docutils literal notranslate"><span class="pre">Token</span></code></a> object that can be used
to restore the variable to its previous value via the
<a class="reference internal" href="#contextvars.ContextVar.reset" title="contextvars.ContextVar.reset"><code class="xref py py-meth docutils literal notranslate"><span class="pre">ContextVar.reset()</span></code></a> method.</p>
</dd></dl>
<dl class="method">
<dt id="contextvars.ContextVar.reset">
<code class="descname">reset</code><span class="sig-paren">(</span><em>token</em><span class="sig-paren">)</span><a class="headerlink" href="#contextvars.ContextVar.reset" title="本定義的永久連結">¶</a></dt>
<dd><p>Reset the context variable to the value it had before the
<a class="reference internal" href="#contextvars.ContextVar.set" title="contextvars.ContextVar.set"><code class="xref py py-meth docutils literal notranslate"><span class="pre">ContextVar.set()</span></code></a> that created the <em>token</em> was used.</p>
<p>For example:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">var</span> <span class="o">=</span> <span class="n">ContextVar</span><span class="p">(</span><span class="s1">'var'</span><span class="p">)</span>
<span class="n">token</span> <span class="o">=</span> <span class="n">var</span><span class="o">.</span><span class="n">set</span><span class="p">(</span><span class="s1">'new value'</span><span class="p">)</span>
<span class="c1"># code that uses 'var'; var.get() returns 'new value'.</span>
<span class="n">var</span><span class="o">.</span><span class="n">reset</span><span class="p">(</span><span class="n">token</span><span class="p">)</span>
<span class="c1"># After the reset call the var has no value again, so</span>
<span class="c1"># var.get() would raise a LookupError.</span>
</pre></div>
</div>
</dd></dl>
</dd></dl>
<dl class="class">
<dt id="contextvars.contextvars.Token">
<em class="property">class </em><code class="descclassname">contextvars.</code><code class="descname">Token</code><a class="headerlink" href="#contextvars.contextvars.Token" title="本定義的永久連結">¶</a></dt>
<dd><p><em>Token</em> objects are returned by the <a class="reference internal" href="#contextvars.ContextVar.set" title="contextvars.ContextVar.set"><code class="xref py py-meth docutils literal notranslate"><span class="pre">ContextVar.set()</span></code></a> method.
They can be passed to the <a class="reference internal" href="#contextvars.ContextVar.reset" title="contextvars.ContextVar.reset"><code class="xref py py-meth docutils literal notranslate"><span class="pre">ContextVar.reset()</span></code></a> method to revert
the value of the variable to what it was before the corresponding
<em>set</em>.</p>
<dl class="attribute">
<dt id="contextvars.contextvars.Token.Token.var">
<code class="descclassname">Token.</code><code class="descname">var</code><a class="headerlink" href="#contextvars.contextvars.Token.Token.var" title="本定義的永久連結">¶</a></dt>
<dd><p>A read-only property. Points to the <a class="reference internal" href="#contextvars.ContextVar" title="contextvars.ContextVar"><code class="xref py py-class docutils literal notranslate"><span class="pre">ContextVar</span></code></a> object
that created the token.</p>
</dd></dl>
<dl class="attribute">
<dt id="contextvars.contextvars.Token.Token.old_value">
<code class="descclassname">Token.</code><code class="descname">old_value</code><a class="headerlink" href="#contextvars.contextvars.Token.Token.old_value" title="本定義的永久連結">¶</a></dt>
<dd><p>A read-only property. Set to the value the variable had before
the <a class="reference internal" href="#contextvars.ContextVar.set" title="contextvars.ContextVar.set"><code class="xref py py-meth docutils literal notranslate"><span class="pre">ContextVar.set()</span></code></a> method call that created the token.
It points to <code class="xref py py-attr docutils literal notranslate"><span class="pre">Token.MISSING</span></code> is the variable was not set
before the call.</p>
</dd></dl>
<dl class="attribute">
<dt id="contextvars.contextvars.Token.Token.MISSING">
<code class="descclassname">Token.</code><code class="descname">MISSING</code><a class="headerlink" href="#contextvars.contextvars.Token.Token.MISSING" title="本定義的永久連結">¶</a></dt>
<dd><p>A marker object used by <code class="xref py py-attr docutils literal notranslate"><span class="pre">Token.old_value</span></code>.</p>
</dd></dl>
</dd></dl>
</div>
<div class="section" id="manual-context-management">
<h2>18.2. Manual Context Management<a class="headerlink" href="#manual-context-management" title="本標題的永久連結">¶</a></h2>
<dl class="function">
<dt id="contextvars.copy_context">
<code class="descclassname">contextvars.</code><code class="descname">copy_context</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#contextvars.copy_context" title="本定義的永久連結">¶</a></dt>
<dd><p>Returns a copy of the current <a class="reference internal" href="#contextvars.Context" title="contextvars.Context"><code class="xref py py-class docutils literal notranslate"><span class="pre">Context</span></code></a> object.</p>
<p>The following snippet gets a copy of the current context and prints
all variables and their values that are set in it:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">ctx</span><span class="p">:</span> <span class="n">Context</span> <span class="o">=</span> <span class="n">copy_context</span><span class="p">()</span>
<span class="nb">print</span><span class="p">(</span><span class="nb">list</span><span class="p">(</span><span class="n">ctx</span><span class="o">.</span><span class="n">items</span><span class="p">()))</span>
</pre></div>
</div>
<p>The function has an O(1) complexity, i.e. works equally fast for
contexts with a few context variables and for contexts that have
a lot of them.</p>
</dd></dl>
<dl class="class">
<dt id="contextvars.Context">
<em class="property">class </em><code class="descclassname">contextvars.</code><code class="descname">Context</code><a class="headerlink" href="#contextvars.Context" title="本定義的永久連結">¶</a></dt>
<dd><p>A mapping of <a class="reference internal" href="#contextvars.ContextVar" title="contextvars.ContextVar"><code class="xref py py-class docutils literal notranslate"><span class="pre">ContextVars</span></code></a> to their values.</p>
<p><code class="docutils literal notranslate"><span class="pre">Context()</span></code> creates an empty context with no values in it.
To get a copy of the current context use the
<a class="reference internal" href="#contextvars.copy_context" title="contextvars.copy_context"><code class="xref py py-func docutils literal notranslate"><span class="pre">copy_context()</span></code></a> function.</p>
<p>Context implements the <a class="reference internal" href="collections.abc.html#collections.abc.Mapping" title="collections.abc.Mapping"><code class="xref py py-class docutils literal notranslate"><span class="pre">collections.abc.Mapping</span></code></a> interface.</p>
<dl class="method">
<dt id="contextvars.Context.run">
<code class="descname">run</code><span class="sig-paren">(</span><em>callable</em>, <em>*args</em>, <em>**kwargs</em><span class="sig-paren">)</span><a class="headerlink" href="#contextvars.Context.run" title="本定義的永久連結">¶</a></dt>
<dd><p>Execute <code class="docutils literal notranslate"><span class="pre">callable(*args,</span> <span class="pre">**kwargs)</span></code> code in the context object
the <em>run</em> method is called on. Return the result of the execution
or propagate an exception if one occurred.</p>
<p>Any changes to any context variables that <em>callable</em> makes will
be contained in the context object:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">var</span> <span class="o">=</span> <span class="n">ContextVar</span><span class="p">(</span><span class="s1">'var'</span><span class="p">)</span>
<span class="n">var</span><span class="o">.</span><span class="n">set</span><span class="p">(</span><span class="s1">'spam'</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
<span class="c1"># 'var' was set to 'spam' before</span>
<span class="c1"># calling 'copy_context()' and 'ctx.run(main)', so:</span>
<span class="c1"># var.get() == ctx[var] == 'spam'</span>
<span class="n">var</span><span class="o">.</span><span class="n">set</span><span class="p">(</span><span class="s1">'ham'</span><span class="p">)</span>
<span class="c1"># Now, after setting 'var' to 'ham':</span>
<span class="c1"># var.get() == ctx[var] == 'ham'</span>
<span class="n">ctx</span> <span class="o">=</span> <span class="n">copy_context</span><span class="p">()</span>
<span class="c1"># Any changes that the 'main' function makes to 'var'</span>
<span class="c1"># will be contained in 'ctx'.</span>
<span class="n">ctx</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">)</span>
<span class="c1"># The 'main()' function was run in the 'ctx' context,</span>
<span class="c1"># so changes to 'var' are contained in it:</span>
<span class="c1"># ctx[var] == 'ham'</span>
<span class="c1"># However, outside of 'ctx', 'var' is still set to 'spam':</span>
<span class="c1"># var.get() == 'spam'</span>
</pre></div>
</div>
<p>The method raises a <a class="reference internal" href="exceptions.html#RuntimeError" title="RuntimeError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">RuntimeError</span></code></a> when called on the same
context object from more than one OS thread, or when called
recursively.</p>
</dd></dl>
<dl class="method">
<dt id="contextvars.Context.copy">
<code class="descname">copy</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#contextvars.Context.copy" title="本定義的永久連結">¶</a></dt>
<dd><p>Return a shallow copy of the context object.</p>
</dd></dl>
<dl class="describe">
<dt>
<code class="descname">var in context</code></dt>
<dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the <em>context</em> has a value for <em>var</em> set;
return <code class="docutils literal notranslate"><span class="pre">False</span></code> otherwise.</p>
</dd></dl>
<dl class="describe">
<dt>
<code class="descname">context[var]</code></dt>
<dd><p>Return the value of the <em>var</em> <a class="reference internal" href="#contextvars.ContextVar" title="contextvars.ContextVar"><code class="xref py py-class docutils literal notranslate"><span class="pre">ContextVar</span></code></a> variable.
If the variable is not set in the context object, a
<a class="reference internal" href="exceptions.html#KeyError" title="KeyError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyError</span></code></a> is raised.</p>
</dd></dl>
<dl class="method">
<dt id="contextvars.Context.get">
<code class="descname">get</code><span class="sig-paren">(</span><em>var</em><span class="optional">[</span>, <em>default</em><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#contextvars.Context.get" title="本定義的永久連結">¶</a></dt>
<dd><p>Return the value for <em>var</em> if <em>var</em> has the value in the context
object. Return <em>default</em> otherwise. If <em>default</em> is not given,
return <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
</dd></dl>
<dl class="describe">
<dt>
<code class="descname">iter(context)</code></dt>
<dd><p>Return an iterator over the variables stored in the context
object.</p>
</dd></dl>
<dl class="describe">
<dt>
<code class="descname">len(proxy)</code></dt>
<dd><p>Return the number of variables set in the context object.</p>
</dd></dl>
<dl class="method">
<dt id="contextvars.Context.keys">
<code class="descname">keys</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#contextvars.Context.keys" title="本定義的永久連結">¶</a></dt>
<dd><p>Return a list of all variables in the context object.</p>
</dd></dl>
<dl class="method">
<dt id="contextvars.Context.values">
<code class="descname">values</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#contextvars.Context.values" title="本定義的永久連結">¶</a></dt>
<dd><p>Return a list of all variables』 values in the context object.</p>
</dd></dl>
<dl class="method">
<dt id="contextvars.Context.items">
<code class="descname">items</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#contextvars.Context.items" title="本定義的永久連結">¶</a></dt>
<dd><p>Return a list of 2-tuples containing all variables and their
values in the context object.</p>
</dd></dl>
</dd></dl>
</div>
<div class="section" id="asyncio-support">
<h2>18.3. asyncio support<a class="headerlink" href="#asyncio-support" title="本標題的永久連結">¶</a></h2>
<p>Context variables are natively supported in <a class="reference internal" href="asyncio.html#module-asyncio" title="asyncio: Asynchronous I/O, event loop, coroutines and tasks."><code class="xref py py-mod docutils literal notranslate"><span class="pre">asyncio</span></code></a> and are
ready to be used without any extra configuration. For example, here
is a simple echo server, that uses a context variable to make the
address of a remote client available in the Task that handles that
client:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">asyncio</span>
<span class="kn">import</span> <span class="nn">contextvars</span>
<span class="n">client_addr_var</span> <span class="o">=</span> <span class="n">contextvars</span><span class="o">.</span><span class="n">ContextVar</span><span class="p">(</span><span class="s1">'client_addr'</span><span class="p">)</span>
<span class="k">def</span> <span class="nf">render_goodbye</span><span class="p">():</span>
<span class="c1"># The address of the currently handled client can be accessed</span>
<span class="c1"># without passing it explicitly to this function.</span>
<span class="n">client_addr</span> <span class="o">=</span> <span class="n">client_addr_var</span><span class="o">.</span><span class="n">get</span><span class="p">()</span>
<span class="k">return</span> <span class="n">f</span><span class="s1">'Good bye, client @ </span><span class="si">{client_addr}</span><span class="se">\n</span><span class="s1">'</span><span class="o">.</span><span class="n">encode</span><span class="p">()</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">handle_request</span><span class="p">(</span><span class="n">reader</span><span class="p">,</span> <span class="n">writer</span><span class="p">):</span>
<span class="n">addr</span> <span class="o">=</span> <span class="n">writer</span><span class="o">.</span><span class="n">transport</span><span class="o">.</span><span class="n">get_extra_info</span><span class="p">(</span><span class="s1">'socket'</span><span class="p">)</span><span class="o">.</span><span class="n">getpeername</span><span class="p">()</span>
<span class="n">client_addr_var</span><span class="o">.</span><span class="n">set</span><span class="p">(</span><span class="n">addr</span><span class="p">)</span>
<span class="c1"># In any code that we call is now possible to get</span>
<span class="c1"># client's address by calling 'client_addr_var.get()'.</span>
<span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
<span class="n">line</span> <span class="o">=</span> <span class="k">await</span> <span class="n">reader</span><span class="o">.</span><span class="n">readline</span><span class="p">()</span>
<span class="nb">print</span><span class="p">(</span><span class="n">line</span><span class="p">)</span>
<span class="k">if</span> <span class="ow">not</span> <span class="n">line</span><span class="o">.</span><span class="n">strip</span><span class="p">():</span>
<span class="k">break</span>
<span class="n">writer</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">line</span><span class="p">)</span>
<span class="n">writer</span><span class="o">.</span><span class="n">write</span><span class="p">(</span><span class="n">render_goodbye</span><span class="p">())</span>
<span class="n">writer</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>
<span class="k">async</span> <span class="k">def</span> <span class="nf">main</span><span class="p">():</span>
<span class="n">srv</span> <span class="o">=</span> <span class="k">await</span> <span class="n">asyncio</span><span class="o">.</span><span class="n">start_server</span><span class="p">(</span>
<span class="n">handle_request</span><span class="p">,</span> <span class="s1">'127.0.0.1'</span><span class="p">,</span> <span class="mi">8081</span><span class="p">)</span>
<span class="k">async</span> <span class="k">with</span> <span class="n">srv</span><span class="p">:</span>
<span class="k">await</span> <span class="n">srv</span><span class="o">.</span><span class="n">serve_forever</span><span class="p">()</span>
<span class="n">asyncio</span><span class="o">.</span><span class="n">run</span><span class="p">(</span><span class="n">main</span><span class="p">())</span>
<span class="c1"># To test it you can use telnet:</span>
<span class="c1"># telnet 127.0.0.1 8081</span>
</pre></div>
</div>
</div>
</div>
</div>
</div>
</div>
<div class="sphinxsidebar" role="navigation" aria-label="main navigation">
<div class="sphinxsidebarwrapper">
<h3><a href="../contents.html">目錄</a></h3>
<ul>
<li><a class="reference internal" href="#">18. <code class="docutils literal notranslate"><span class="pre">contextvars</span></code> — Context Variables</a><ul>
<li><a class="reference internal" href="#context-variables">18.1. Context Variables</a></li>
<li><a class="reference internal" href="#manual-context-management">18.2. Manual Context Management</a></li>
<li><a class="reference internal" href="#asyncio-support">18.3. asyncio support</a></li>
</ul>
</li>
</ul>
<h4>上個主題</h4>
<p class="topless"><a href="dummy_threading.html"
title="上一章">17.10. <code class="docutils literal notranslate"><span class="pre">dummy_threading</span></code> — Drop-in replacement for the <code class="docutils literal notranslate"><span class="pre">threading</span></code> module</a></p>
<h4>下個主題</h4>
<p class="topless"><a href="ipc.html"
title="下一章">19. Interprocess Communication and Networking</a></p>
<div role="note" aria-label="source link">
<h3>This Page</h3>
<ul class="this-page-menu">
<li><a href="../bugs.html">Report a Bug</a></li>
<li>
<a href="https://github.com/python/cpython/blob/3.7/Doc/library/contextvars.rst"
rel="nofollow">Show Source
</a>
</li>
</ul>
</div>
</div>
</div>
<div class="clearer"></div>
</div>
<div class="related" role="navigation" aria-label="related navigation">
<h3>瀏覽</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="../genindex.html" title="General Index"
>索引</a></li>
<li class="right" >
<a href="../py-modindex.html" title="Python 模組索引"
>模組</a> |</li>
<li class="right" >
<a href="ipc.html" title="19. Interprocess Communication and Networking"
>下一頁</a> |</li>
<li class="right" >
<a href="dummy_threading.html" title="17.10. dummy_threading — Drop-in replacement for the threading module"
>上一頁</a> |</li>
<li><img src="../_static/py.png" alt=""
style="vertical-align: middle; margin-top: -1px"/></li>
<li><a href="https://www.python.org/">Python</a> »</li>
<li>
<span class="language_switcher_placeholder">zh_TW</span>
<span class="version_switcher_placeholder">3.7.0</span>
<a href="../index.html">Documentation </a> »
</li>
<li class="nav-item nav-item-1"><a href="index.html" >Python 標準函式庫 (Standard Library)</a> »</li>
<li class="right">
<div class="inline-search" style="display: none" role="search">
<form class="inline-search" action="../search.html" method="get">
<input placeholder="Quick search" type="text" name="q" />
<input type="submit" value="Go" />
<input type="hidden" name="check_keywords" value="yes" />
<input type="hidden" name="area" value="default" />
</form>
</div>
<script type="text/javascript">$('.inline-search').show(0);</script>
|
</li>
</ul>
</div>
<div class="footer">
© <a href="../copyright.html">Copyright</a> 2001-2018, Python Software Foundation.
<br />
The Python Software Foundation is a non-profit corporation.
<a href="https://www.python.org/psf/donations/">Please donate.</a>
<br />
Last updated on 8月 22, 2018.
<a href="../bugs.html">Found a bug</a>?
<br />
Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.7.7.
</div>
</body>
</html>