Here you can see the full list of changes between each Flask release.
(bugfix release, released on June 14th 2013)
- Fixed an issue where |tojson was 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 were registering the same method twice for the same endpoint
would trigger an exception incorrectly.
Released on June 13nd 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.
- Added template_test methods in addition to the already existing
template_filter method family.
- Added template_global methods in addition to the already existing
template_filter method family.
- Set the content-length header for x-sendfile.
- tojson filter now does not escape script blocks in HTML5 parsers.
- tojson used 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.session module alias. Use
flask.sessions instead to get the session module. This is not to
be confused with flask.session the session proxy.
- Templates can now be rendered without request context. The behavior is
slightly different as the request, session and g objects
will not be available and blueprint’s context processors are not
- 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.dumps to return bytestrings by default.
- flask.g is now stored on the app context instead of the request
- flask.g now gained a get() method for not erroring out on non
- flask.g now can be used with the in operator to see what’s defined
and it now is iterable and will yield all attributes stored.
- flask.Flask.request_globals_class got renamed to
flask.Flask.app_ctx_globals_class which 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
- 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
- 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 JSONIFY_PRETTYPRINT_REGULAR configuration variable.
- 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_NAME into account when
picking the default port to run on.
- Added flask.request.get_json() as a replacement for the old
Released on July 1st 2012, codename Campari.
- The flask.Request.on_json_loading_failed() now returns a JSON formatted
response by default.
- The flask.url_for() function now can generate anchors to the
- The 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
- Unregister a circular dependency between the WSGI environment and
the request object when shutting down the request. This means that
environ werkzeug.request will be None after 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
- The flask.Flask class 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,
- The flask.get_flashed_messages() function now allows rendering flashed
message categories in separate blocks, through a category_filter
- The flask.Flask.run() method now accepts None for 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.
- The 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.
- Added 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
instance of flask.Response. This allows for returning
jsonify(error="error msg"), 400 from a view function.
- Flask and Blueprint now 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_DEFAULT configuration 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.
- Added flask.Flask.request_globals_class to allow a specific class to
be used on creation of the g instance of each request.
- Added required_methods attribute to view functions to force-add methods
- Added flask.after_this_request().
- Added 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
- 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. (Flask.before_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
conceptionally 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 APPLICATION_ROOT configuration variable.
- Implemented session_transaction() to
easily modify sessions from the test environment.
- Refactored test client internally. The APPLICATION_ROOT configuration
variable as well as SERVER_NAME are now properly used by the test client
- Added flask.views.View.decorators to 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.ext package 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
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
- Added make_default_options_response()
which can be used by subclasses to alter the default
behavior for OPTIONS responses.
- Unbound locals now raise a proper RuntimeError instead
of an AttributeError.
- Mimetype guessing and etag support based on file objects is now
deprecated for 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
- fixed a problem for Flask to run on jython.
- added a PROPAGATE_EXCEPTIONS configuration variable that can be
used to flip the setting of exception propagation which previously
was linked to DEBUG alone and is now linked to either DEBUG or
- 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
- 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
- Implemented flask.has_request_context()
- Deprecated init_jinja_globals. Override the
create_jinja_environment() method instead to
achieve the same functionality.
- Added flask.safe_join()
- The automatic JSON request data unpacking now looks at the charset
- 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 OPTIONS response was
not exposing all valid methods in the Allow header.
- Jinja2 template loading syntax now allows ”./” in front of
a template load path. Previously this caused issues with
- 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
- 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
- the config is now available in the templates
- context processors will no longer override values passed directly
to the render function.
- added the ability to limit the incoming request data with the
new MAX_CONTENT_LENGTH configuration value.
- 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 create_url_adapter()
- modules can now register for a subdomain instead of just an URL
prefix. This makes it possible to bind a whole module to a
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
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
the SERVER_NAME config 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 .html, .htm, .xml and .xhtml.
Inside templates this behavior can be changed with the
- refactored Flask internally. It now consists of more than a
- 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
- after_request() handlers are now also invoked
if the request dies with an exception and an error handling page
- 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.
- added TESTING switch that can activate unittesting helpers.
- the logger switches to DEBUG mode now if debug is enabled.
Bugfix release, released on May 28th 2010
- fixed a error reporting bug with flask.Config.from_envvar()
- 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.Handler and will
log request handling exceptions to that logger when not in debug
mode. This makes it possible to receive mails on server errors
- 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
- added get_template_attribute() helper function.
- add_url_rule() can now also register a
- 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 send_file()
- 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.