Here you can see the full list of changes between each Flask release.
Major release, unreleased
- Make app.run() into a noop if a Flask application is run from the development server on the command line. This avoids some behavior that was confusing to debug for newcomers.
- Change default configuration JSONIFY_PRETTYPRINT_REGULAR=False. jsonify() method returns compressed response by default, and pretty response in debug mode.
- Change Flask.__init__ to accept two new keyword arguments,
static_host. This enables
host_matchingto be set properly by the time the constructor adds the static route, and enables the static route to be properly associated with the required host. (
send_filesupports Unicode in
Bugfix release, released on March 31st 2017
- Prevent flask run from showing a NoAppException when an ImportError occurs within the imported application module.
- Fix encoding behavior of
app.config.from_pyfilefor Python 3. Fix
- Use the
SERVER_NAMEconfig if it is present as default values for
- Call ctx.auto_pop with the exception object instead of None, in the event that a BaseException such as KeyboardInterrupt is raised in a request handler.
Released on December 21st 2016, codename Punsch.
- the cli command now responds to –version.
- Mimetype guessing and ETag generation for file-like objects in
send_filehas been removed, as per issue
#104. See pull request
- Mimetype guessing in
send_filenow fails loudly and doesn’t fall back to
application/octet-stream. See pull request
flask.safe_joinable to join multiple paths like
- Revert a behavior change that made the dev server crash instead of returning
a Internal Server Error (pull request
- Correctly invoke response handlers for both regular request dispatching as well as error handlers.
- Disable logger propagation by default for the app logger.
- Add support for range requests in
app.test_clientincludes preset default environment, which can now be directly set, instead of per
Bugfix release, unreleased
- Fix crash when running under PyPy3, see pull request
Bugfix release, released on June 7th 2016.
- Fixed a bug that prevented
FLASK_APP=foobar/__init__.pyfrom working. See pull request
Released on May 29th 2016, codename Absinthe.
- 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
SESSION_REFRESH_EACH_REQUESTconfig key that controls the set-cookie behavior. If set to
Truea permanent session will be refreshed each request and get their lifetime extended, if set to
Falseit 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.
- Templates are no longer automatically reloaded outside of debug mode. This
can be configured with the new
- 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 flask and the
flask.climodule 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
- Error handlers that match specific classes are now checked first,
thereby allowing catching exceptions that are subclasses of HTTP
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.
- 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
- Removed deprecated module functionality.
- Added the
EXPLAIN_TEMPLATE_LOADINGconfig 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.
request.jsonin favour of
- 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
OPTIONSmethod is now correctly disabled if the user registered an overriding rule with the lowercase-version
flask.json.jsonifynow supports the
datetime.datetype (pull request
- Don’t leak exception info of already catched exceptions to context teardown
handlers (pull request
- Allow custom Jinja environment subclasses (pull request
- Turn on autoescape for
flask.templating.render_template_stringby default (pull request
flask.extis now deprecated (pull request
send_from_directorynow raises BadRequest if the filename is invalid on the server OS (pull request
- Added the
JSONIFY_MIMETYPEconfiguration variable (pull request
- Exceptions during teardown handling will no longer leave bad application contexts lingering around.
(bugfix release, release date to be announced)
- Fixed broken test_appcontext_signals() test case.
- Raise an
flask.helpers.find_package()with a useful message explaining why it is raised when a PEP 302 import hook is used without an is_package() method.
- Fixed an issue causing exceptions raised before entering a request or app context to be passed to teardown handlers.
- Fixed an issue with query parameters getting removed from requests in the test client when absolute URLs were requested.
- Made @before_first_request into a decorator as intended.
- Fixed an etags bug when sending a file streams with a name.
- Fixed send_from_directory not expanding to the application root path correctly.
- Changed logic of before first request handlers to flip the flag after invoking. This will allow some uses that are potentially dangerous but should probably be permitted.
- Fixed Python 3 bug when a handler from app.url_build_error_handlers reraises the BuildError.
(bugfix release, released on June 14th 2013)
- Fixed an issue where
|tojsonwas not quoting single quotes which made the filter not work properly in HTML attributes. Now it’s possible to use that filter in single quoted attributes. This should make using that filter with angular.js easier.
- Added support for byte strings back to the session system. This broke compatibility with the common case of people putting binary data for token verification into the session.
- Fixed an issue where registering the same method twice for the same endpoint would trigger an exception incorrectly.
Released on June 13th 2013, codename Limoncello.
- Changed default cookie serialization format from pickle to JSON to limit the impact an attacker can do if the secret key leaks. See Version 0.10 for more information.
template_testmethods in addition to the already existing
template_globalmethods in addition to the already existing
- Set the content-length header for x-sendfile.
tojsonfilter now does not escape script blocks in HTML5 parsers.
tojsonused in templates is now safe by default due. This was allowed due to the different escaping behavior.
- Flask will now raise an error if you attempt to register a new function on an already used endpoint.
- Added wrapper module around simplejson and added default serialization of datetime objects. This allows much easier customization of how JSON is handled by Flask or any Flask extension.
- Removed deprecated internal
flask.sessionmodule alias. Use
flask.sessionsinstead to get the session module. This is not to be confused with
flask.sessionthe session proxy.
- Templates can now be rendered without request context. The behavior is
slightly different as the
gobjects will not be available and blueprint’s context processors are not called.
- The config object is now available to the template as a real global and not through a context processor which makes it available even in imported templates by default.
- Added an option to generate non-ascii encoded JSON which should result
in less bytes being transmitted over the network. It’s disabled by
default to not cause confusion with existing libraries that might expect
flask.json.dumpsto return bytestrings by default.
flask.gis now stored on the app context instead of the request context.
flask.gnow gained a
get()method for not erroring out on non existing items.
flask.gnow can be used with the
inoperator to see what’s defined and it now is iterable and will yield all attributes stored.
flask.Flask.request_globals_classgot renamed to
flask.Flask.app_ctx_globals_classwhich is a better name to what it does since 0.10.
- request, session and g are now also added as proxies to the template context which makes them available in imported templates. One has to be very careful with those though because usage outside of macros might cause caching.
- Flask will no longer invoke the wrong error handlers if a proxy exception is passed through.
- Added a workaround for chrome’s cookies in localhost not working as intended with domain names.
- Changed logic for picking defaults for cookie values from sessions to work better with Google Chrome.
- Added message_flashed signal that simplifies flashing testing.
- Added support for copying of request contexts for better working with greenlets.
- Removed custom JSON HTTP exception subclasses. If you were relying on them you can reintroduce them again yourself trivially. Using them however is strongly discouraged as the interface was flawed.
- Python requirements changed: requiring Python 2.6 or 2.7 now to prepare for Python 3.3 port.
- Changed how the teardown system is informed about exceptions. This is now more reliable in case something handles an exception halfway through the error handling process.
- Request context preservation in debug mode now keeps the exception information around which means that teardown handlers are able to distinguish error from success cases.
- Added the
- Flask now orders JSON keys by default to not trash HTTP caches due to different hash seeds between different workers.
- Added appcontext_pushed and appcontext_popped signals.
- The builtin run method now takes the
SERVER_NAMEinto account when picking the default port to run on.
- Added flask.request.get_json() as a replacement for the old flask.request.json property.
Released on July 1st 2012, codename Campari.
flask.Request.on_json_loading_failed()now returns a JSON formatted response by default.
flask.url_for()function now can generate anchors to the generated links.
flask.url_for()function now can also explicitly generate URL rules specific to a given HTTP method.
- Logger now only returns the debug log setting if it was not set explicitly.
- Unregister a circular dependency between the WSGI environment and
the request object when shutting down the request. This means that
Noneafter the response was returned to the WSGI server but has the advantage that the garbage collector is not needed on CPython to tear down the request unless the user created circular dependencies themselves.
- Session is now stored after callbacks so that if the session payload is stored in the session you can still modify it in an after request callback.
flask.Flaskclass will avoid importing the provided import name if it can (the required first parameter), to benefit tools which build Flask instances programmatically. The Flask class will fall back to using import on systems with custom module hooks, e.g. Google App Engine, or when the import name is inside a zip archive (usually a .egg) prior to Python 2.7.
- Blueprints now have a decorator to add custom template filters application
- The Flask and Blueprint classes now have a non-decorator method for adding
custom template filters application wide,
flask.get_flashed_messages()function now allows rendering flashed message categories in separate blocks, through a
flask.Flask.run()method now accepts
Nonefor host and port arguments, using default values when
None. This allows for calling run using configuration values, e.g.
app.run(app.config.get('MYHOST'), app.config.get('MYPORT')), with proper behavior whether or not a config file is provided.
flask.render_template()method now accepts a either an iterable of template names or a single template name. Previously, it only accepted a single template name. On an iterable, the first template found is rendered.
flask.Flask.app_context()which works very similar to the request context but only provides access to the current application. This also adds support for URL generation without an active request context.
- View functions can now return a tuple with the first instance being an
flask.Response. This allows for returning
jsonify(error="error msg"), 400from a view function.
Blueprintnow provide a
get_send_file_max_age()hook for subclasses to override behavior of serving static files from Flask when using
flask.Flask.send_static_file()(used for the default static file handler) and
send_file(). This hook is provided a filename, which for example allows changing cache controls by file extension. The default max-age for send_file and static files can be configured through a new
SEND_FILE_MAX_AGE_DEFAULTconfiguration variable, which is used in the default get_send_file_max_age implementation.
- Fixed an assumption in sessions implementation which could break message flashing on sessions implementations which use external storage.
- Changed the behavior of tuple return values from functions. They are no longer arguments to the response object, they now have a defined meaning.
flask.Flask.request_globals_classto allow a specific class to be used on creation of the
ginstance of each request.
- Added required_methods attribute to view functions to force-add methods on registration.
flask.stream_with_context()and the ability to push contexts multiple times without producing unexpected behavior.
Bugfix release, released on July 1st 2012
- Fixed an issue with the undocumented flask.session module to not work properly on Python 2.5. It should not be used but did cause some problems for package managers.
Released on September 29th 2011, codename Rakija
- Refactored session support into a session interface so that the implementation of the sessions can be changed without having to override the Flask class.
- Empty session cookies are now deleted properly automatically.
- View functions can now opt out of getting the automatic OPTIONS implementation.
- HTTP exceptions and Bad Request errors can now be trapped so that they show up normally in the traceback.
- Flask in debug mode is now detecting some common problems and tries to warn you about them.
- Flask in debug mode will now complain with an assertion error if a view was attached after the first request was handled. This gives earlier feedback when users forget to import view code ahead of time.
- Added the ability to register callbacks that are only triggered once at
the beginning of the first request. (
- Malformed JSON data will now trigger a bad request HTTP exception instead of a value error which usually would result in a 500 internal server error if not handled. This is a backwards incompatible change.
- Applications now not only have a root path where the resources and modules are located but also an instance path which is the designated place to drop files that are modified at runtime (uploads etc.). Also this is conceptually only instance depending and outside version control so it’s the perfect place to put configuration files etc. For more information see Instance Folders.
- Added the
session_transaction()to easily modify sessions from the test environment.
- Refactored test client internally. The
APPLICATION_ROOTconfiguration variable as well as
SERVER_NAMEare now properly used by the test client as defaults.
flask.views.View.decoratorsto support simpler decorating of pluggable (class-based) views.
- Fixed an issue where the test client if used with the “with” statement did not trigger the execution of the teardown handlers.
- Added finer control over the session cookie parameters.
- HEAD requests to a method view now automatically dispatch to the get method if no handler was implemented.
- Implemented the virtual
flask.extpackage to import extensions from.
- The context preservation on exceptions is now an integral component of Flask itself and no longer of the test client. This cleaned up some internal logic and lowers the odds of runaway request contexts in unittests.
Bugfix release, release date to be decided
- Fixed the Jinja2 environment’s list_templates method not returning the correct names when blueprints or modules were involved.
Bugfix release, released on July 6th 2011
- Fixed an issue with URL processors not properly working on blueprints.
Bugfix release, released on June 29th 2011
- Added missing future import that broke 2.5 compatibility.
- Fixed an infinite redirect issue with blueprints.
Released on June 28th 2011, codename Grappa
make_default_options_response()which can be used by subclasses to alter the default behavior for
- Unbound locals now raise a proper
RuntimeErrorinstead of an
- Mimetype guessing and etag support based on file objects is now
flask.send_file()because it was unreliable. Pass filenames instead or attach your own etags and provide a proper mimetype by hand.
- Static file handling for modules now requires the name of the static folder to be supplied explicitly. The previous autodetection was not reliable and caused issues on Google’s App Engine. Until 1.0 the old behavior will continue to work but issue dependency warnings.
- fixed a problem for Flask to run on jython.
- added a
PROPAGATE_EXCEPTIONSconfiguration variable that can be used to flip the setting of exception propagation which previously was linked to
DEBUGalone and is now linked to either
- Flask no longer internally depends on rules being added through the add_url_rule function and can now also accept regular werkzeug rules added to the url map.
- Added an endpoint method to the flask application object which allows one to register a callback to an arbitrary endpoint with a decorator.
- Use Last-Modified for static file sending instead of Date which was incorrectly introduced in 0.6.
- Added create_jinja_loader to override the loader creation process.
- Implemented a silent flag for config.from_pyfile.
- Added teardown_request decorator, for functions that should run at the end of a request regardless of whether an exception occurred. Also the behavior for after_request was changed. It’s now no longer executed when an exception is raised. See Upgrading to new Teardown Handling
- Deprecated init_jinja_globals. Override the
create_jinja_environment()method instead to achieve the same functionality.
- The automatic JSON request data unpacking now looks at the charset mimetype parameter.
- Don’t modify the session on
flask.get_flashed_messages()if there are no messages in the session.
- before_request handlers are now able to abort requests with errors.
- it is not possible to define user exception handlers. That way you can provide custom error messages from a central hub for certain errors that might occur during request processing (for instance database connection errors, timeouts from remote resources etc.).
- Blueprints can provide blueprint specific error handlers.
- Implemented generic Pluggable Views (class-based views).
Bugfix release, released on December 31st 2010
- Fixed an issue where the default
OPTIONSresponse was not exposing all valid methods in the
- Jinja2 template loading syntax now allows ”./” in front of a template load path. Previously this caused issues with module setups.
- Fixed an issue where the subdomain setting for modules was ignored for the static folder.
- Fixed a security problem that allowed clients to download arbitrary files if the host server was a windows based operating system and the client uses backslashes to escape the directory the files where exposed from.
Released on July 27th 2010, codename Whisky
- after request functions are now called in reverse order of registration.
- OPTIONS is now automatically implemented by Flask unless the application explicitly adds ‘OPTIONS’ as method to the URL rule. In this case no automatic OPTIONS handling kicks in.
- static rules are now even in place if there is no static folder for the module. This was implemented to aid GAE which will remove the static folder if it’s part of a mapping in the .yml file.
configis now available in the templates as config.
- context processors will no longer override values passed directly to the render function.
- added the ability to limit the incoming request data with the
- the endpoint for the
flask.Module.add_url_rule()method is now optional to be consistent with the function of the same name on the application object.
- added a
flask.make_response()function that simplifies creating response object instances in views.
- added signalling support based on blinker. This feature is currently optional and supposed to be used by extensions and applications. If you want to use it, make sure to have blinker installed.
- refactored the way URL adapters are created. This process is now
fully customizable with the
- modules can now register for a subdomain instead of just an URL prefix. This makes it possible to bind a whole module to a configurable subdomain.
Bugfix Release, released on July 15th 2010
- fixed another issue with loading templates from directories when modules were used.
Bugfix Release, released on July 6th 2010
- fixes an issue with template loading from directories when modules where used.
Released on July 6th 2010, codename Calvados
- fixed a bug with subdomains that was caused by the inability to
specify the server name. The server name can now be set with
SERVER_NAMEconfig key. This key is now also used to set the session cookie cross-subdomain wide.
- autoescaping is no longer active for all templates. Instead it
is only active for
.xhtml. Inside templates this behavior can be changed with the
- refactored Flask internally. It now consists of more than a single file.
flask.send_file()now emits etags and has the ability to do conditional responses builtin.
- (temporarily) dropped support for zipped applications. This was a rarely used feature and led to some confusing behavior.
- added support for per-package template and static-file directories.
- removed support for create_jinja_loader which is no longer used in 0.5 due to the improved module support.
- added a helper function to expose files from any directory.
Released on June 18th 2010, codename Rakia
- added the ability to register application wide error handlers from modules.
after_request()handlers are now also invoked if the request dies with an exception and an error handling page kicks in.
- test client has not the ability to preserve the request context for a little longer. This can also be used to trigger custom requests that do not pop the request stack for testing.
- because the Python standard library caches loggers, the name of the logger is configurable now to better support unittests.
TESTINGswitch that can activate unittesting helpers.
- the logger switches to
DEBUGmode now if debug is enabled.
Bugfix release, released on May 28th 2010
- fixed a error reporting bug with
- removed some unused code from flask
- release does no longer include development leftover files (.git folder for themes, built documentation in zip and pdf file and some .pyc files)
Released on May 28th 2010, codename Schnaps
- added support for categories for flashed messages.
- the application now configures a
logging.Handlerand will log request handling exceptions to that logger when not in debug mode. This makes it possible to receive mails on server errors for example.
- added support for context binding that does not require the use of the with statement for playing in the console.
- the request context is now available within the with statement making it possible to further push the request context or pop it.
- added support for configurations.
Released on May 12th 2010, codename Jägermeister
- various bugfixes
- integrated JSON support
add_url_rule()can now also register a view function.
- refactored internal request dispatching.
- server listens on 127.0.0.1 by default now to fix issues with chrome.
- added external URL support.
- added support for
- module support and internal request handling refactoring to better support pluggable applications.
- sessions can be set to be permanent now on a per-session basis.
- better error reporting on missing secret keys.
- added support for Google Appengine.
First public preview release.