When a new version of Pyramid is released, it will sometimes deprecate a feature or remove a feature that was deprecated in an older release. When features are removed from Pyramid, applications that depend on those features will begin to break. This chapter explains how to ensure your Pyramid applications keep working when you upgrade the Pyramid version you’re using.
The Pyramid core team is conservative when it comes to removing features. We don’t remove features unnecessarily, but we’re human, and we make mistakes which cause some features to be evolutionary dead ends. Though we are willing to support dead-end features for some amount of time, some eventually have to be removed when the cost of supporting them outweighs the benefit of keeping them around, because each feature in Pyramid represents a certain documentation and maintenance burden.
When a feature is scheduled for removal from Pyramid or any of its official add-ons, the core development team takes these steps:
When a deprecated feature is eventually removed:
Features are never removed in micro releases. They are only removed in minor and major releases. Deprecated features are kept around for at least three minor releases from the time the feature became deprecated. Therefore, if a feature is added in Pyramid 1.0, but it’s deprecated in Pyramid 1.1, it will be kept around through all 1.1.X releases, all 1.2.X releases and all 1.3.X releases. It will finally be removed in the first 1.4.X release.
Sometimes features are “docs-deprecated” instead of formally deprecated. This means that the feature will be kept around indefinitely, but it will be removed from the documentation or a note will be added to the documentation telling folks to use some other newer feature. This happens when the cost of keeping an old feature around is very minimal and the support and documentation burden is very low. For example, we might rename a function that is an API without changing the arguments it accepts. In this case, we’ll often rename the function, and change the docs to point at the new function name, but leave around a backwards compatibility alias to the old function name so older code doesn’t break.
“Docs deprecated” features tend to work “forever”, meaning that they won’t be removed, and they’ll never generate a deprecation warning. However, such changes are noted in the Pyramid Change History, so it’s possible to know that you should change older spellings to newer ones to ensure that people reading your code can find the APIs you’re using in the Pyramid docs.
Your first line of defense against application failures caused by upgrading to a newer Pyramid release is always to read the Pyramid Change History. to find the deprecations and removals for each release between the release you’re currently running and the one you wish to upgrade to. The change history notes every deprecation within a Deprecation section and every removal within a Backwards Incompatibilies section for each release.
The change history often contains instructions for changing your code to avoid deprecation warnings and how to change docs-deprecated spellings to newer ones. You can follow along with each deprecation explanation in the change history, simply doing a grep or other code search to your application, using the change log examples to remediate each potential problem.
Once you’ve upgraded your application to a new Pyramid release and you’ve remediated as much as possible by using the change history notes, you’ll want to run your application’s tests (see Run the Tests) in such a way that you can see DeprecationWarnings printed to the console when the tests run.
$ python -Wd setup.py test -q
The -Wd argument is an argument that tells Python to print deprecation warnings to the console. Note that the -Wd flag is only required for Python 2.7 and better: Python versions 2.6 and older print deprecation warnings to the console by default. See the Python -W flag documentation for more information.
As your tests run, deprecation warnings will be printed to the console explaining the deprecation and providing instructions about how to prevent the deprecation warning from being issued. For example:
$ python -Wd setup.py test -q # .. elided ... running build_ext /home/chrism/projects/pyramid/env27/myproj/myproj/views.py:3: DeprecationWarning: static: The "pyramid.view.static" class is deprecated as of Pyramid 1.1; use the "pyramid.static.static_view" class instead with the "use_subpath" argument set to True. from pyramid.view import static . ---------------------------------------------------------------------- Ran 1 test in 0.014s OK
In the above case, it’s line #3 in the myproj.views module (from pyramid.view import static) that is causing the problem:
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from pyramid.view import view_config from pyramid.view import static myview = static('static', 'static')
The deprecation warning tells me how to fix it, so I can change the code to do things the newer way:
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from pyramid.view import view_config from pyramid.static import static_view myview = static_view('static', 'static', use_subpath=True)
When I run the tests again, the deprecation warning is no longer printed to my console:
$ python -Wd setup.py test -q # .. elided ... running build_ext . ---------------------------------------------------------------------- Ran 1 test in 0.014s OK
If your application has no tests, or has only moderate test coverage, running tests won’t tell you very much, because the Pyramid codepaths that generate deprecation warnings won’t be executed.
In this circumstance, you can start your application interactively under a server run with the PYTHONWARNINGS environment variable set to default. On UNIX, you can do that via:
$ PYTHONWARNINGS=default bin/pserve development.ini
On Windows, you need to issue two commands:
C:\> set PYTHONWARNINGS=default C:\> Scripts/pserve.exe development.ini
At this point, it’s ensured that deprecation warnings will be printed to the console whenever a codepath is hit that generates one. You can then click around in your application interactively to try to generate them, and remediate as explained in Testing Your Application Under a New Pyramid Release.
See the PYTHONWARNINGS environment variable documentation or the Python -W flag documentation for more information.
When you upgrade your application to the very most recent Pyramid release, it’s advisable to upgrade step-wise through each most recent minor release, beginning with the one that you know your application currently runs under, and ending on the most recent release. For example, if your application is running in production on Pyramid 1.2.1, and the most recent Pyramid 1.3 release is Pyramid 1.3.3, and the most recent Pyramid release is 1.4.4, it’s advisable to do this:
If you skip testing your application under each minor release (for example if you upgrade directly from 1.2.1 to 1.4.4), you might miss a deprecation warning and waste more time trying to figure out an error caused by a feature removal than it would take to upgrade stepwise through each minor release.