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
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
|
<!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">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Configuration Handling — Flask 0.8 documentation</title>
<link rel="stylesheet" href="_static/flasky.css" type="text/css" />
<link rel="stylesheet" href="_static/pygments.css" type="text/css" />
<script type="text/javascript">
var DOCUMENTATION_OPTIONS = {
URL_ROOT: '',
VERSION: '0.8',
COLLAPSE_INDEX: false,
FILE_SUFFIX: '.html',
HAS_SOURCE: true
};
</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>
<link rel="top" title="Flask 0.8 documentation" href="index.html" />
<link rel="next" title="Signals" href="signals.html" />
<link rel="prev" title="Handling Application Errors" href="errorhandling.html" />
<link rel="apple-touch-icon" href="_static/touch-icon.png" />
<link media="only screen and (max-device-width: 480px)" href="_static/small_flask.css" type= "text/css" rel="stylesheet" />
</head>
<body>
<div class="related">
<h3>Navigation</h3>
<ul>
<li class="right" style="margin-right: 10px">
<a href="genindex.html" title="General Index"
accesskey="I">index</a></li>
<li class="right" >
<a href="signals.html" title="Signals"
accesskey="N">next</a> |</li>
<li class="right" >
<a href="errorhandling.html" title="Handling Application Errors"
accesskey="P">previous</a> |</li>
<li><a href="index.html">Flask 0.8 documentation</a> »</li>
</ul>
</div>
<div class="document">
<div class="documentwrapper">
<div class="bodywrapper">
<div class="body">
<div class="section" id="configuration-handling">
<span id="config"></span><h1>Configuration Handling<a class="headerlink" href="#configuration-handling" title="Permalink to this headline">¶</a></h1>
<p class="versionadded">
<span class="versionmodified">New in version 0.3.</span></p>
<p>Applications need some kind of configuration. There are different settings
you might want to change depending on the application environment like
toggling the debug mode, setting the secret key, and other such
environment-specific things.</p>
<p>The way Flask is designed usually requires the configuration to be
available when the application starts up. You can hardcode the
configuration in the code, which for many small applications is not
actually that bad, but there are better ways.</p>
<p>Independent of how you load your config, there is a config object
available which holds the loaded configuration values:
The <a class="reference internal" href="api.html#flask.Flask.config" title="flask.Flask.config"><tt class="xref py py-attr docutils literal"><span class="pre">config</span></tt></a> attribute of the <a class="reference internal" href="api.html#flask.Flask" title="flask.Flask"><tt class="xref py py-class docutils literal"><span class="pre">Flask</span></tt></a>
object. This is the place where Flask itself puts certain configuration
values and also where extensions can put their configuration values. But
this is also where you can have your own configuration.</p>
<div class="section" id="configuration-basics">
<h2>Configuration Basics<a class="headerlink" href="#configuration-basics" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference internal" href="api.html#flask.Flask.config" title="flask.Flask.config"><tt class="xref py py-attr docutils literal"><span class="pre">config</span></tt></a> is actually a subclass of a dictionary and
can be modified just like any dictionary:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span> <span class="o">=</span> <span class="n">Flask</span><span class="p">(</span><span class="n">__name__</span><span class="p">)</span>
<span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="p">[</span><span class="s">'DEBUG'</span><span class="p">]</span> <span class="o">=</span> <span class="bp">True</span>
</pre></div>
</div>
<p>Certain configuration values are also forwarded to the
<a class="reference internal" href="api.html#flask.Flask" title="flask.Flask"><tt class="xref py py-attr docutils literal"><span class="pre">Flask</span></tt></a> object so you can read and write them from there:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span><span class="o">.</span><span class="n">debug</span> <span class="o">=</span> <span class="bp">True</span>
</pre></div>
</div>
<p>To update multiple keys at once you can use the <a class="reference external" href="http://docs.python.org/dev/library/stdtypes.html#dict.update" title="(in Python v3.3)"><tt class="xref py py-meth docutils literal"><span class="pre">dict.update()</span></tt></a>
method:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">update</span><span class="p">(</span>
<span class="n">DEBUG</span><span class="o">=</span><span class="bp">True</span><span class="p">,</span>
<span class="n">SECRET_KEY</span><span class="o">=</span><span class="s">'...'</span>
<span class="p">)</span>
</pre></div>
</div>
</div>
<div class="section" id="builtin-configuration-values">
<h2>Builtin Configuration Values<a class="headerlink" href="#builtin-configuration-values" title="Permalink to this headline">¶</a></h2>
<p>The following configuration values are used internally by Flask:</p>
<table border="1" class="docutils">
<colgroup>
<col width="45%" />
<col width="55%" />
</colgroup>
<tbody valign="top">
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">DEBUG</span></tt></td>
<td>enable/disable debug mode</td>
</tr>
<tr class="row-even"><td><tt class="docutils literal"><span class="pre">TESTING</span></tt></td>
<td>enable/disable testing mode</td>
</tr>
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">PROPAGATE_EXCEPTIONS</span></tt></td>
<td>explicitly enable or disable the
propagation of exceptions. If not set or
explicitly set to <cite>None</cite> this is
implicitly true if either <cite>TESTING</cite> or
<cite>DEBUG</cite> is true.</td>
</tr>
<tr class="row-even"><td><tt class="docutils literal"><span class="pre">PRESERVE_CONTEXT_ON_EXCEPTION</span></tt></td>
<td>By default if the application is in
debug mode the request context is not
popped on exceptions to enable debuggers
to introspect the data. This can be
disabled by this key. You can also use
this setting to force-enable it for non
debug execution which might be useful to
debug production applications (but also
very risky).</td>
</tr>
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">SECRET_KEY</span></tt></td>
<td>the secret key</td>
</tr>
<tr class="row-even"><td><tt class="docutils literal"><span class="pre">SESSION_COOKIE_NAME</span></tt></td>
<td>the name of the session cookie</td>
</tr>
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">SESSION_COOKIE_DOMAIN</span></tt></td>
<td>the domain for the session cookie. If
this is not set, the cookie will be
valid for all subdomains of
<tt class="docutils literal"><span class="pre">SERVER_NAME</span></tt>.</td>
</tr>
<tr class="row-even"><td><tt class="docutils literal"><span class="pre">SESSION_COOKIE_PATH</span></tt></td>
<td>the path for the session cookie. If
this is not set the cookie will be valid
for all of <tt class="docutils literal"><span class="pre">APPLICATION_ROOT</span></tt> or if
that is not set for <tt class="docutils literal"><span class="pre">'/'</span></tt>.</td>
</tr>
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">SESSION_COOKIE_HTTPONLY</span></tt></td>
<td>controls if the cookie should be set
with the httponly flag. Defaults to
<cite>True</cite>.</td>
</tr>
<tr class="row-even"><td><tt class="docutils literal"><span class="pre">SESSION_COOKIE_SECURE</span></tt></td>
<td>controls if the cookie should be set
with the secure flag. Defaults to
<cite>False</cite>.</td>
</tr>
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">PERMANENT_SESSION_LIFETIME</span></tt></td>
<td>the lifetime of a permanent session as
<a class="reference external" href="http://docs.python.org/dev/library/datetime.html#datetime.timedelta" title="(in Python v3.3)"><tt class="xref py py-class docutils literal"><span class="pre">datetime.timedelta</span></tt></a> object.
Starting with Flask 0.8 this can also be
an integer representing seconds.</td>
</tr>
<tr class="row-even"><td><tt class="docutils literal"><span class="pre">USE_X_SENDFILE</span></tt></td>
<td>enable/disable x-sendfile</td>
</tr>
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">LOGGER_NAME</span></tt></td>
<td>the name of the logger</td>
</tr>
<tr class="row-even"><td><tt class="docutils literal"><span class="pre">SERVER_NAME</span></tt></td>
<td>the name and port number of the server.
Required for subdomain support (e.g.:
<tt class="docutils literal"><span class="pre">'myapp.dev:5000'</span></tt>) Note that
localhost does not support subdomains so
setting this to “localhost” does not
help.</td>
</tr>
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">APPLICATION_ROOT</span></tt></td>
<td>If the application does not occupy
a whole domain or subdomain this can
be set to the path where the application
is configured to live. This is for
session cookie as path value. If
domains are used, this should be
<tt class="docutils literal"><span class="pre">None</span></tt>.</td>
</tr>
<tr class="row-even"><td><tt class="docutils literal"><span class="pre">MAX_CONTENT_LENGTH</span></tt></td>
<td>If set to a value in bytes, Flask will
reject incoming requests with a
content length greater than this by
returning a 413 status code.</td>
</tr>
<tr class="row-odd"><td><tt class="docutils literal"><span class="pre">TRAP_HTTP_EXCEPTIONS</span></tt></td>
<td>If this is set to <tt class="docutils literal"><span class="pre">True</span></tt> Flask will
not execute the error handlers of HTTP
exceptions but instead treat the
exception like any other and bubble it
through the exception stack. This is
helpful for hairy debugging situations
where you have to find out where an HTTP
exception is coming from.</td>
</tr>
<tr class="row-even"><td><tt class="docutils literal"><span class="pre">TRAP_BAD_REQUEST_ERRORS</span></tt></td>
<td>Werkzeug’s internal data structures that
deal with request specific data will
raise special key errors that are also
bad request exceptions. Likewise many
operations can implicitly fail with a
BadRequest exception for consistency.
Since it’s nice for debugging to know
why exactly it failed this flag can be
used to debug those situations. If this
config is set to <tt class="docutils literal"><span class="pre">True</span></tt> you will get
a regular traceback instead.</td>
</tr>
</tbody>
</table>
<div class="admonition-more-on-server-name admonition ">
<p class="first admonition-title">More on <tt class="docutils literal"><span class="pre">SERVER_NAME</span></tt></p>
<p>The <tt class="docutils literal"><span class="pre">SERVER_NAME</span></tt> key is used for the subdomain support. Because
Flask cannot guess the subdomain part without the knowledge of the
actual server name, this is required if you want to work with
subdomains. This is also used for the session cookie.</p>
<p class="last">Please keep in mind that not only Flask has the problem of not knowing
what subdomains are, your web browser does as well. Most modern web
browsers will not allow cross-subdomain cookies to be set on a
server name without dots in it. So if your server name is
<tt class="docutils literal"><span class="pre">'localhost'</span></tt> you will not be able to set a cookie for
<tt class="docutils literal"><span class="pre">'localhost'</span></tt> and every subdomain of it. Please chose a different
server name in that case, like <tt class="docutils literal"><span class="pre">'myapplication.local'</span></tt> and add
this name + the subdomains you want to use into your host config
or setup a local <a class="reference external" href="https://www.isc.org/software/bind">bind</a>.</p>
</div>
<p class="versionadded">
<span class="versionmodified">New in version 0.4: </span><tt class="docutils literal"><span class="pre">LOGGER_NAME</span></tt></p>
<p class="versionadded">
<span class="versionmodified">New in version 0.5: </span><tt class="docutils literal"><span class="pre">SERVER_NAME</span></tt></p>
<p class="versionadded">
<span class="versionmodified">New in version 0.6: </span><tt class="docutils literal"><span class="pre">MAX_CONTENT_LENGTH</span></tt></p>
<p class="versionadded">
<span class="versionmodified">New in version 0.7: </span><tt class="docutils literal"><span class="pre">PROPAGATE_EXCEPTIONS</span></tt>, <tt class="docutils literal"><span class="pre">PRESERVE_CONTEXT_ON_EXCEPTION</span></tt></p>
<p class="versionadded">
<span class="versionmodified">New in version 0.8: </span><tt class="docutils literal"><span class="pre">TRAP_BAD_REQUEST_ERRORS</span></tt>, <tt class="docutils literal"><span class="pre">TRAP_HTTP_EXCEPTIONS</span></tt>,
<tt class="docutils literal"><span class="pre">APPLICATION_ROOT</span></tt>, <tt class="docutils literal"><span class="pre">SESSION_COOKIE_DOMAIN</span></tt>,
<tt class="docutils literal"><span class="pre">SESSION_COOKIE_PATH</span></tt>, <tt class="docutils literal"><span class="pre">SESSION_COOKIE_HTTPONLY</span></tt>,
<tt class="docutils literal"><span class="pre">SESSION_COOKIE_SECURE</span></tt></p>
</div>
<div class="section" id="configuring-from-files">
<h2>Configuring from Files<a class="headerlink" href="#configuring-from-files" title="Permalink to this headline">¶</a></h2>
<p>Configuration becomes more useful if you can store it in a separate file,
ideally located outside the actual application package. This makes
packaging and distributing your application possible via various package
handling tools (<a class="reference internal" href="patterns/distribute.html#distribute-deployment"><em>Deploying with Distribute</em></a>) and finally modifying the
configuration file afterwards.</p>
<p>So a common pattern is this:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span> <span class="o">=</span> <span class="n">Flask</span><span class="p">(</span><span class="n">__name__</span><span class="p">)</span>
<span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">from_object</span><span class="p">(</span><span class="s">'yourapplication.default_settings'</span><span class="p">)</span>
<span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">from_envvar</span><span class="p">(</span><span class="s">'YOURAPPLICATION_SETTINGS'</span><span class="p">)</span>
</pre></div>
</div>
<p>This first loads the configuration from the
<cite>yourapplication.default_settings</cite> module and then overrides the values
with the contents of the file the <span class="target" id="index-0"></span><tt class="xref std std-envvar docutils literal"><span class="pre">YOURAPPLICATION_SETTINGS</span></tt>
environment variable points to. This environment variable can be set on
Linux or OS X with the export command in the shell before starting the
server:</p>
<div class="highlight-python"><pre>$ export YOURAPPLICATION_SETTINGS=/path/to/settings.cfg
$ python run-app.py
* Running on http://127.0.0.1:5000/
* Restarting with reloader...</pre>
</div>
<p>On Windows systems use the <cite>set</cite> builtin instead:</p>
<div class="highlight-python"><pre>>set YOURAPPLICATION_SETTINGS=\path\to\settings.cfg</pre>
</div>
<p>The configuration files themselves are actual Python files. Only values
in uppercase are actually stored in the config object later on. So make
sure to use uppercase letters for your config keys.</p>
<p>Here is an example of a configuration file:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="c"># Example configuration</span>
<span class="n">DEBUG</span> <span class="o">=</span> <span class="bp">False</span>
<span class="n">SECRET_KEY</span> <span class="o">=</span> <span class="s">'?</span><span class="se">\xbf</span><span class="s">,</span><span class="se">\xb4\x8d\xa3</span><span class="s">"<</span><span class="se">\x9c\xb0</span><span class="s">@</span><span class="se">\x0f</span><span class="s">5</span><span class="se">\xab</span><span class="s">,w</span><span class="se">\xee\x8d</span><span class="s">$0</span><span class="se">\x13\x8b</span><span class="s">83'</span>
</pre></div>
</div>
<p>Make sure to load the configuration very early on, so that extensions have
the ability to access the configuration when starting up. There are other
methods on the config object as well to load from individual files. For a
complete reference, read the <a class="reference internal" href="api.html#flask.Config" title="flask.Config"><tt class="xref py py-class docutils literal"><span class="pre">Config</span></tt></a> object’s
documentation.</p>
</div>
<div class="section" id="configuration-best-practices">
<h2>Configuration Best Practices<a class="headerlink" href="#configuration-best-practices" title="Permalink to this headline">¶</a></h2>
<p>The downside with the approach mentioned earlier is that it makes testing
a little harder. There is no single 100% solution for this problem in
general, but there are a couple of things you can keep in mind to improve
that experience:</p>
<ol class="arabic simple">
<li>create your application in a function and register blueprints on it.
That way you can create multiple instances of your application with
different configurations attached which makes unittesting a lot
easier. You can use this to pass in configuration as needed.</li>
<li>Do not write code that needs the configuration at import time. If you
limit yourself to request-only accesses to the configuration you can
reconfigure the object later on as needed.</li>
</ol>
</div>
<div class="section" id="development-production">
<h2>Development / Production<a class="headerlink" href="#development-production" title="Permalink to this headline">¶</a></h2>
<p>Most applications need more than one configuration. There should be at
least separate configurations for the production server and the one used
during development. The easiest way to handle this is to use a default
configuration that is always loaded and part of the version control, and a
separate configuration that overrides the values as necessary as mentioned
in the example above:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span> <span class="o">=</span> <span class="n">Flask</span><span class="p">(</span><span class="n">__name__</span><span class="p">)</span>
<span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">from_object</span><span class="p">(</span><span class="s">'yourapplication.default_settings'</span><span class="p">)</span>
<span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">from_envvar</span><span class="p">(</span><span class="s">'YOURAPPLICATION_SETTINGS'</span><span class="p">)</span>
</pre></div>
</div>
<p>Then you just have to add a separate <cite>config.py</cite> file and export
<tt class="docutils literal"><span class="pre">YOURAPPLICATION_SETTINGS=/path/to/config.py</span></tt> and you are done. However
there are alternative ways as well. For example you could use imports or
subclassing.</p>
<p>What is very popular in the Django world is to make the import explicit in
the config file by adding an <tt class="docutils literal"><span class="pre">from</span> <span class="pre">yourapplication.default_settings</span>
<span class="pre">import</span> <span class="pre">*</span></tt> to the top of the file and then overriding the changes by hand.
You could also inspect an environment variable like
<tt class="docutils literal"><span class="pre">YOURAPPLICATION_MODE</span></tt> and set that to <cite>production</cite>, <cite>development</cite> etc
and import different hardcoded files based on that.</p>
<p>An interesting pattern is also to use classes and inheritance for
configuration:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">class</span> <span class="nc">Config</span><span class="p">(</span><span class="nb">object</span><span class="p">):</span>
<span class="n">DEBUG</span> <span class="o">=</span> <span class="bp">False</span>
<span class="n">TESTING</span> <span class="o">=</span> <span class="bp">False</span>
<span class="n">DATABASE_URI</span> <span class="o">=</span> <span class="s">'sqlite://:memory:'</span>
<span class="k">class</span> <span class="nc">ProductionConfig</span><span class="p">(</span><span class="n">Config</span><span class="p">):</span>
<span class="n">DATABASE_URI</span> <span class="o">=</span> <span class="s">'mysql://user@localhost/foo'</span>
<span class="k">class</span> <span class="nc">DevelopmentConfig</span><span class="p">(</span><span class="n">Config</span><span class="p">):</span>
<span class="n">DEBUG</span> <span class="o">=</span> <span class="bp">True</span>
<span class="k">class</span> <span class="nc">TestingConfig</span><span class="p">(</span><span class="n">Config</span><span class="p">):</span>
<span class="n">TESTING</span> <span class="o">=</span> <span class="bp">True</span>
</pre></div>
</div>
<p>To enable such a config you just have to call into
<a class="reference internal" href="api.html#flask.Config.from_object" title="flask.Config.from_object"><tt class="xref py py-meth docutils literal"><span class="pre">from_object()</span></tt></a>:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">from_object</span><span class="p">(</span><span class="s">'configmodule.ProductionConfig'</span><span class="p">)</span>
</pre></div>
</div>
<p>There are many different ways and it’s up to you how you want to manage
your configuration files. However here a list of good recommendations:</p>
<ul class="simple">
<li>keep a default configuration in version control. Either populate the
config with this default configuration or import it in your own
configuration files before overriding values.</li>
<li>use an environment variable to switch between the configurations.
This can be done from outside the Python interpreter and makes
development and deployment much easier because you can quickly and
easily switch between different configs without having to touch the
code at all. If you are working often on different projects you can
even create your own script for sourcing that activates a virtualenv
and exports the development configuration for you.</li>
<li>Use a tool like <a class="reference external" href="http://fabfile.org/">fabric</a> in production to push code and
configurations separately to the production server(s). For some
details about how to do that, head over to the
<a class="reference internal" href="patterns/fabric.html#fabric-deployment"><em>Deploying with Fabric</em></a> pattern.</li>
</ul>
</div>
<div class="section" id="instance-folders">
<span id="id1"></span><h2>Instance Folders<a class="headerlink" href="#instance-folders" title="Permalink to this headline">¶</a></h2>
<p class="versionadded">
<span class="versionmodified">New in version 0.8.</span></p>
<p>Flask 0.8 introduces instance folders. Flask for a long time made it
possible to refer to paths relative to the application’s folder directly
(via <tt class="xref py py-attr docutils literal"><span class="pre">Flask.root_path</span></tt>). This was also how many developers loaded
configurations stored next to the application. Unfortunately however this
only works well if applications are not packages in which case the root
path refers to the contents of the package.</p>
<p>With Flask 0.8 a new attribute was introduced:
<tt class="xref py py-attr docutils literal"><span class="pre">Flask.instance_path</span></tt>. It refers to a new concept called the
“instance folder”. The instance folder is designed to not be under
version control and be deployment specific. It’s the perfect place to
drop things that either change at runtime or configuration files.</p>
<p>You can either explicitly provide the path of the instance folder when
creating the Flask application or you can let Flask autodetect the
instance folder. For explicit configuration use the <cite>instance_path</cite>
parameter:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span> <span class="o">=</span> <span class="n">Flask</span><span class="p">(</span><span class="n">__name__</span><span class="p">,</span> <span class="n">instance_path</span><span class="o">=</span><span class="s">'/path/to/instance/folder'</span><span class="p">)</span>
</pre></div>
</div>
<p>Please keep in mind that this path <em>must</em> be absolute when provided.</p>
<p>If the <cite>instance_path</cite> parameter is not provided the following default
locations are used:</p>
<ul>
<li><p class="first">Uninstalled module:</p>
<div class="highlight-python"><pre>/myapp.py
/instance</pre>
</div>
</li>
<li><p class="first">Uninstalled package:</p>
<div class="highlight-python"><pre>/myapp
/__init__.py
/instance</pre>
</div>
</li>
<li><p class="first">Installed module or package:</p>
<div class="highlight-python"><pre>$PREFIX/lib/python2.X/site-packages/myapp
$PREFIX/var/myapp-instance</pre>
</div>
<p><tt class="docutils literal"><span class="pre">$PREFIX</span></tt> is the prefix of your Python installation. This can be
<tt class="docutils literal"><span class="pre">/usr</span></tt> or the path to your virtualenv. You can print the value of
<tt class="docutils literal"><span class="pre">sys.prefix</span></tt> to see what the prefix is set to.</p>
</li>
</ul>
<p>Since the config object provided loading of configuration files from
relative filenames we made it possible to change the loading via filenames
to be relative to the instance path if wanted. The behavior of relative
paths in config files can be flipped between “relative to the application
root” (the default) to “relative to instance folder” via the
<cite>instance_relative_config</cite> switch to the application constructor:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span> <span class="o">=</span> <span class="n">Flask</span><span class="p">(</span><span class="n">__name__</span><span class="p">,</span> <span class="n">instance_relative_config</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
</pre></div>
</div>
<p>Here is a full example of how to configure Flask to preload the config
from a module and then override the config from a file in the config
folder if it exists:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">app</span> <span class="o">=</span> <span class="n">Flask</span><span class="p">(</span><span class="n">__name__</span><span class="p">,</span> <span class="n">instance_relative_config</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
<span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">from_object</span><span class="p">(</span><span class="s">'yourapplication.default_settings'</span><span class="p">)</span>
<span class="n">app</span><span class="o">.</span><span class="n">config</span><span class="o">.</span><span class="n">from_pyfile</span><span class="p">(</span><span class="s">'application.cfg'</span><span class="p">,</span> <span class="n">silent</span><span class="o">=</span><span class="bp">True</span><span class="p">)</span>
</pre></div>
</div>
<p>The path to the instance folder can be found via the
<tt class="xref py py-attr docutils literal"><span class="pre">Flask.instance_path</span></tt>. Flask also provides a shortcut to open a
file from the instance folder with <tt class="xref py py-meth docutils literal"><span class="pre">Flask.open_instance_resource()</span></tt>.</p>
<p>Example usage for both:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">filename</span> <span class="o">=</span> <span class="n">os</span><span class="o">.</span><span class="n">path</span><span class="o">.</span><span class="n">join</span><span class="p">(</span><span class="n">app</span><span class="o">.</span><span class="n">instance_root</span><span class="p">,</span> <span class="s">'application.cfg'</span><span class="p">)</span>
<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="n">filename</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="n">config</span> <span class="o">=</span> <span class="n">f</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
<span class="c"># or via open_instance_resource:</span>
<span class="k">with</span> <span class="n">app</span><span class="o">.</span><span class="n">open_instance_resource</span><span class="p">(</span><span class="s">'application.cfg'</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
<span class="n">config</span> <span class="o">=</span> <span class="n">f</span><span class="o">.</span><span class="n">read</span><span class="p">()</span>
</pre></div>
</div>
</div>
</div>
</div>
</div>
</div>
<div class="sphinxsidebar">
<div class="sphinxsidebarwrapper"><p class="logo"><a href="index.html">
<img class="logo" src="_static/flask.png" alt="Logo"/>
</a></p>
<h3><a href="index.html">Table Of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#">Configuration Handling</a><ul>
<li><a class="reference internal" href="#configuration-basics">Configuration Basics</a></li>
<li><a class="reference internal" href="#builtin-configuration-values">Builtin Configuration Values</a></li>
<li><a class="reference internal" href="#configuring-from-files">Configuring from Files</a></li>
<li><a class="reference internal" href="#configuration-best-practices">Configuration Best Practices</a></li>
<li><a class="reference internal" href="#development-production">Development / Production</a></li>
<li><a class="reference internal" href="#instance-folders">Instance Folders</a></li>
</ul>
</li>
</ul>
<h3>Related Topics</h3>
<ul>
<li><a href="index.html">Documentation overview</a><ul>
<li>Previous: <a href="errorhandling.html" title="previous chapter">Handling Application Errors</a></li>
<li>Next: <a href="signals.html" title="next chapter">Signals</a></li>
</ul></li>
</ul>
<h3>This Page</h3>
<ul class="this-page-menu">
<li><a href="_sources/config.txt"
rel="nofollow">Show Source</a></li>
</ul>
<div id="searchbox" style="display: none">
<h3>Quick search</h3>
<form class="search" action="search.html" method="get">
<input 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>
<p class="searchtip" style="font-size: 90%">
Enter search terms or a module, class or function name.
</p>
</div>
<script type="text/javascript">$('#searchbox').show(0);</script>
</div>
</div>
<div class="clearer"></div>
</div>
<div class="footer">
© Copyright 2010, Armin Ronacher.
Created using <a href="http://sphinx.pocoo.org/">Sphinx</a>.
</div>
</body>
</html>
|
