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Upgrading to Newer Releases

Flask itself is changing like any software is changing over time. Most of the changes are the nice kind, the kind where you don't have to change anything in your code to profit from a new release.

However every once in a while there are changes that do require some changes in your code or there are changes that make it possible for you to improve your own code quality by taking advantage of new features in Flask.

This section of the documentation enumerates all the changes in Flask from release to release and how you can change your code to have a painless updating experience.

If you want to use the easy_install command to upgrade your Flask installation, make sure to pass it the -U parameter:

$ easy_install -U Flask

Version 0.7

Due to a bug in earlier implementations the request local proxies now raise a :exc:`RuntimeError` instead of an :exc:`AttributeError` when they are unbound. If you caught these exceptions with :exc:`AttributeError` before, you should catch them with :exc:`RuntimeError` now.

Additionally the :func:`~flask.send_file` function is now issuing deprecation warnings if you depend on functionality that will be removed in Flask 1.0. Previously it was possible to use etags and mimetypes when file objects were passed. This was unreliable and caused issues for a few setups. If you get a deprecation warning, make sure to update your application to work with either filenames there or disable etag attaching and attach them yourself.

Old code:

return send_file(my_file_object)
return send_file(my_file_object)

New code:

return send_file(my_file_object, add_etags=False)

Version 0.6

Flask 0.6 comes with a backwards incompatible change which affects the order of after-request handlers. Previously they were called in the order of the registration, now they are called in reverse order. This change was made so that Flask behaves more like people expected it to work and how other systems handle request pre- and postprocessing. If you dependend on the order of execution of post-request functions, be sure to change the order.

Another change that breaks backwards compatibility is that context processors will no longer override values passed directly to the template rendering function. If for example request is as variable passed directly to the template, the default context processor will not override it with the current request object. This makes it easier to extend context processors later to inject additional variables without breaking existing template not expecting them.

Version 0.5

Flask 0.5 is the first release that comes as a Python package instead of a single module. There were a couple of internal refactoring so if you depend on undocumented internal details you probably have to adapt the imports.

The following changes may be relevant to your application:

  • autoescaping no longer happens for all templates. Instead it is configured to only happen on files ending with .html, .htm, .xml and .xhtml. If you have templates with different extensions you should override the :meth:`~flask.Flask.select_jinja_autoescape` method.
  • Flask no longer supports zipped applications in this release. This functionality might come back in future releases if there is demand for this feature. Removing support for this makes the Flask internal code easier to understand and fixes a couple of small issues that make debugging harder than necessary.
  • The create_jinja_loader function is gone. If you want to customize the Jinja loader now, use the :meth:`~flask.Flask.create_jinja_environment` method instead.

Version 0.4

For application developers there are no changes that require changes in your code. In case you are developing on a Flask extension however, and that extension has a unittest-mode you might want to link the activation of that mode to the new TESTING flag.

Version 0.3

Flask 0.3 introduces configuration support and logging as well as categories for flashing messages. All these are features that are 100% backwards compatible but you might want to take advantage of them.

Configuration Support

The configuration support makes it easier to write any kind of application that requires some sort of configuration. (Which most likely is the case for any application out there).

If you previously had code like this:

app.debug = DEBUG
app.secret_key = SECRET_KEY

You no longer have to do that, instead you can just load a configuration into the config object. How this works is outlined in :ref:`config`.

Logging Integration

Flask now configures a logger for you with some basic and useful defaults. If you run your application in production and want to profit from automatic error logging, you might be interested in attaching a proper log handler. Also you can start logging warnings and errors into the logger when appropriately. For more information on that, read :ref:`old-logging`.

Categories for Flash Messages

Flash messages can now have categories attached. This makes it possible to render errors, warnings or regular messages differently for example. This is an opt-in feature because it requires some rethinking in the code.

Read all about that in the :ref:`message-flashing-pattern` pattern.

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