Flask 0.11 Released

written by Armin Ronacher on 2016-05-29 in Releases

After a very long, long waiting time Flask finally got a new release. There really was no good reason that there has not been a release in such a long time but unfortunately once things are postponed for too long a certain release anxiety kicks in.

In this case this was long tagged as 1.0 but we decided for renaming it to 0.11 and back out some of the more controversial changes. In particular the new command line interface for Flask was modified a bit to not depend on some specific functionality in the supporting Click library.

Highlights of this release are the improved development experience which now stalls the browser on reload instead of bringing up a "connection reset" page and the new command line support.

Future Plans

This is also the first Flask release under the new pallets organization and from now on we hope to bring you releases more frequently. Ideally with the next release we also update the website to find a new home for the showcase, flask extension list as well as the snippet section to allow the community to take care of those things themselves.


  • Added support to serializing top-level arrays to flask.jsonify. This introduces a security risk in ancient browsers. See json-security for details.
  • Added before_render_template signal.
  • Added **kwargs to flask.Test.test_client to support passing additional keyword arguments to the constructor of flask.Flask.test_client_class.
  • Added SESSION_REFRESH_EACH_REQUEST config key that controls the set-cookie behavior. If set to True a permanent session will be refreshed each request and get their lifetime extended, if set to False it will only be modified if the session actually modifies. Non permanent sessions are not affected by this and will always expire if the browser window closes.
  • Made Flask support custom JSON mimetypes for incoming data.
  • Added support for returning tuples in the form (response, headers) from a view function.
  • Added flask.Config.from_json.
  • Added flask.Flask.config_class.
  • Added flask.config.Config.get_namespace.
  • Templates are no longer automatically reloaded outside of debug mode. This can be configured with the new TEMPLATES_AUTO_RELOAD config key.
  • Added a workaround for a limitation in Python 3.3's namespace loader.
  • Added support for explicit root paths when using Python 3.3's namespace packages.
  • Added the flask command and the flask.cli module to start the local debug server through the click CLI system. This is recommended over the old flask.run() method as it works faster and more reliable due to a different design and also replaces Flask-Script.
  • Error handlers that match specific classes are now checked first, thereby allowing catching exceptions that are subclasses of HTTP exceptions (in werkzeug.exceptions). This makes it possible for an extension author to create exceptions that will by default result in the HTTP error of their choosing, but may be caught with a custom error handler if desired.
  • Added flask.Config.from_mapping.
  • Flask will now log by default even if debug is disabled. The log format is now hardcoded but the default log handling can be disabled through the LOGGER_HANDLER_POLICY configuration key.
  • Removed deprecated module functionality.
  • Added the EXPLAIN_TEMPLATE_LOADING config flag which when enabled will instruct Flask to explain how it locates templates. This should help users debug when the wrong templates are loaded.
  • Enforce blueprint handling in the order they were registered for template loading.
  • Ported test suite to py.test.
  • Deprecated request.json in favour of request.get_json().
  • Add "pretty" and "compressed" separators definitions in jsonify() method. Reduces JSON response size when JSONIFY_PRETTYPRINT_REGULAR=False by removing unnecessary white space included by default after separators.
  • JSON responses are now terminated with a newline character, because it is a convention that UNIX text files end with a newline and some clients don't deal well when this newline is missing. See https://github.com/pallets/flask/pull/1262 -- this came up originally as a part of https://github.com/kennethreitz/httpbin/issues/168
  • The automatically provided OPTIONS method is now correctly disabled if the user registered an overriding rule with the lowercase-version options (issue #1288).
  • flask.json.jsonify now supports the datetime.date type (pull request #1326).
  • Don't leak exception info of already caught exceptions to context teardown handlers (pull request #1393).
  • Allow custom Jinja environment subclasses (pull request #1422).
  • flask.g now has pop() and setdefault methods.
  • Turn on autoescape for flask.templating.render_template_string by default (pull request #1515).
  • flask.ext is now deprecated (pull request #1484).
  • send_from_directory now raises BadRequest if the filename is invalid on the server OS (pull request #1763).
  • Added the JSONIFY_MIMETYPE configuration variable (pull request #1728).
  • Exceptions during teardown handling will no longer leave bad application contexts lingering around.