Drop support for Python 2 and 3.5.
JSON support no longer uses simplejson. To use another JSON module, override
encodingoption to JSON functions is deprecated. #3562
script_infoto app factory functions is deprecated. This was not portable outside the
click.get_current_context().objif it’s needed. #3552
The CLI shows better error messages when the app failed to load when looking up commands. #2741
flask runcommand will only defer errors on reload. Errors present during the initial call will cause the server to exit with the traceback immediately. #3431
When using ad-hoc certificates, check for the cryptography library instead of PyOpenSSL. #3492
When specifying a factory function with
FLASK_APP, keyword argument can be passed. #3553
When loading a
.flaskenvfile, the current working directory is no longer changed to the location of the file. #3560
When returning a
(response, headers)tuple from a view, the headers replace rather than extend existing headers on the response. For example, this allows setting the
response.headers.extend()if extending is desired. #3628
Scaffoldclass provides a common API for the
Blueprintinformation is stored in attributes just like
Flask, rather than opaque lambda functions. This is intended to improve consistency and maintainability. #3215
Not yet released.
flask.json_availableflag was added back for compatibility with some extensions. It will raise a deprecation warning when used, and will be removed in version 2.0.0. #3288
Bump minimum Werkzeug version to >= 0.15.
Drop support for Python 3.4.
Error handlers for
500will always be passed an instance of
InternalServerError. If they are invoked due to an unhandled exception, that original exception is now available as
e.original_exceptionrather than being passed directly to the handler. The same is true if the handler is for the base
HTTPException. This makes error handler behavior more consistent. #3266
Flask.finalize_request()is called for all unhandled exceptions even if there is no
Flask.loggertakes the same name as
Flask.name(the value passed as
Flask(import_name). This reverts 1.0’s behavior of always logging to
"flask.app", in order to support multiple apps in the same process. A warning will be shown if old configuration is detected that needs to be moved. #2866
flask.RequestContext.copy()includes the current session object in the request context copy. This prevents
sessionpointing to an out-of-date object. #2935
Using built-in RequestContext, unprintable Unicode characters in Host header will result in a HTTP 400 response and not HTTP 500 as previously. #2994
open_resource()accepts the “rt” file mode. This still does the same thing as “r”. #3163
MethodView.methodsattribute set in a base class is used by subclasses. #3138
JSONMixinfor the request and response wrappers was moved into Werkzeug. Use Werkzeug’s version with Flask-specific support. This bumps the Werkzeug dependency to >= 0.15. #3125
flaskcommand entry point is simplified to take advantage of Werkzeug 0.15’s better reloader support. This bumps the Werkzeug dependency to >= 0.15. #3022
static_url_paththat ends with a forward slash. #3134
static_folderwithout requiring setting an empty
static_url_pathas well. #3124
The development server port can be set to 0, which tells the OS to pick an available port. #2926
Signaling support has a stub for the
connect_viamethod when the Blinker library is not installed. #3208
--extra-filesoption to the
flask runCLI command to specify extra files that will trigger the reloader on change. #2897
Allow returning a dictionary from a view function. Similar to how returning a string will produce a
text/htmlresponse, returning a dict will call
jsonifyto produce a
Blueprints have a
cliClick group like
app.cli. CLI commands registered with a blueprint will be available as a group under the
When using the test client as a context manager (
with client:), all preserved request contexts are popped when the block exits, ensuring nested contexts are cleaned up correctly. #3157
Show a better error message when the view return type is not supported. #3214
flask.testing.make_test_environ_builder()has been deprecated in favour of a new class
flask runcommand no longer fails if Python is not built with SSL support. Using the
--certoption will show an appropriate error message. #3211
URL matching now occurs after the request context is pushed, rather than when it’s created. This allows custom URL converters to access the app and request contexts, such as to query a database for an id. #3088
The key information for
BadRequestKeyErroris no longer cleared outside debug mode, so error handlers can still access it. This requires upgrading to Werkzeug 0.15.5. #3249
send_fileurl quotes the “:” and “/” characters for more compatible UTF-8 filename support in some browsers. #3074
Fixes for PEP451 import loaders and pytest 5.x. #3275
Show message about dotenv on stderr instead of stdout. #3285
Allow custom CLIs using
FlaskGroupto set the debug flag without it always being overwritten based on environment variables. #2765
flask --versionoutputs Werkzeug’s version and simplifies the Python version. #2825
A catch-all error handler registered for
HTTPExceptionwill not handle
RoutingException, which is used internally during routing. This fixes the unexpected behavior that had been introduced in 1.0. #2986
app.test_clientdoes not push/pop an extra app context. #2900
Fix registering partials (with no
__name__) as view functions. #2730
Don’t treat lists returned from view functions the same as tuples. Only tuples are interpreted as response data. #2736
BadRequestKeyErrorerrors in debug mode, not all
BadRequesterrors. This allows
abort(400)to continue working as expected. #2735
FLASK_SKIP_DOTENVenvironment variable can be set to
1to skip automatically loading dotenv files. #2722
Python 2.6 and 3.3 are no longer supported.
Bump minimum dependency versions to the latest stable versions: Werkzeug >= 0.14, Jinja >= 2.10, itsdangerous >= 0.24, Click >= 5.1. #2586
app.runwhen a Flask application is run from the command line. This avoids some behavior that was confusing to debug.
Errors caused while opening the session at the beginning of the request are handled by the app’s error handlers. #2254
routesCLI command to output routes registered on the application. #2259
Show warning when session cookie domain is a bare hostname or an IP address, as these may not behave properly in some browsers, such as Chrome. #2282
Allow IP address as exact session cookie domain. #2282
SESSION_COOKIE_DOMAINis set if it is detected through
Auto-detect zero-argument app factory called
Factory functions are not required to take a
script_infoparameter to work with the
flaskcommand. If they take a single parameter or a parameter named
ScriptInfoobject will be passed. #2319
FLASK_APPcan be set to an app factory, with arguments if needed, for example
FLASK_APPcan point to local packages that are not installed in editable mode, although
pip install -eis still preferred. #2414
Error handling will try handlers registered for
app, exception. #2314
Cookieis added to the response’s
Varyheader if the session is accessed at all during the request (and not deleted). #2288
'/'by default. This was already the implicit default when it was set to
jsonkeyword argument for the test client request methods. This will dump the given object as JSON and set the appropriate content type. #2358
Removed error handler caching because it caused unexpected results for some exception inheritance hierarchies. Register handlers explicitly for each exception if you want to avoid traversing the MRO. #2362
Fix incorrect JSON encoding of aware, non-UTC datetimes. #2374
The following old deprecated code was removed. #2385
flask.ext- import extensions directly by their name instead of through the
flask.extnamespace. For example,
Flask.error_handlers- tracked by
Flask.errorhandler()to register handlers.
Flask.loggerhas been simplified.
LOGGER_HANDLER_POLICYconfig was removed. The logger is always named
flask.app. The level is only set on first access, it doesn’t check
Flask.debugeach time. Only one format is used, not different ones depending on
Flask.debug. No handlers are removed, and a handler is only added if no handlers are already configured. #2436
Blueprint view function names may not contain dots. #2450
ValueErrorcaused by invalid
Rangerequests in some cases. #2526
The development server uses threads by default. #2529
flask runto run the development server over HTTPS. #2606
A single trailing slash is stripped from the blueprint
url_prefixwhen it is registered with the app. #2629
Updated documentation theme to make docs look better in small windows. #2709
Rewrote the tutorial docs and example project to take a more structured approach to help new users avoid common pitfalls. #2676
Fix a Python warning about imports when using
python -m flask. #2666
ValueErrorcaused by invalid
Rangerequests in some cases.
Fix a bug in
flask runfrom showing a
ImportErroroccurs within the imported application module.
Fix encoding behavior of
app.config.from_pyfilefor Python 3. #2118
ctx.auto_popwith the exception object instead of
None, in the event that a
KeyboardInterruptis raised in a request handler.
Released 2016-12-21, codename Punsch
The cli command now responds to
Mimetype guessing and ETag generation for file-like objects in
send_filehas been removed. #104, :pr`1849`
Mimetype guessing in
send_filenow fails loudly and doesn’t fall back to
flask.safe_joinable to join multiple paths like
Revert a behavior change that made the dev server crash instead of returning an Internal Server Error. #2006
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
Fix crash when running under PyPy3. #1814
Fixed a bug that prevented
FLASK_APP=foobar/__init__.pyfrom working. #1872
Released 2016-05-29, codename Absinthe
Added support to serializing top-level arrays to
flask.jsonify(). This introduces a security risk in ancient browsers.
Added before_render_template signal.
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 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.
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.
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=Falseby 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. This came up originally as a part of https://github.com/postmanlabs/httpbin/issues/168. #1262
The automatically provided
OPTIONSmethod is now correctly disabled if the user registered an overriding rule with the lowercase-version
flask.json.jsonifynow supports the
Don’t leak exception info of already caught exceptions to context teardown handlers. #1393
Allow custom Jinja environment subclasses. #1422
Updated extension dev guidelines.
Turn on autoescape for
flask.templating.render_template_stringby default. #1515
flask.extis now deprecated. #1484
send_from_directorynow raises BadRequest if the filename is invalid on the server OS. #1763
JSONIFY_MIMETYPEconfiguration variable. #1728
Exceptions during teardown handling will no longer leave bad application contexts lingering around.
flask.helpers.find_package()with a useful message explaining why it is raised when a PEP 302 import hook is used without an
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.
@before_first_requestinto a decorator as intended.
Fixed an etags bug when sending a file streams with a name.
send_from_directorynot 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
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 2013-06-13, codename Limoncello
Changed default cookie serialization format from pickle to JSON to limit the impact an attacker can do if the secret key leaks.
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 bytes 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.
gare 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.
message_flashedsignal 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.
Flask now orders JSON keys by default to not trash HTTP caches due to different hash seeds between different workers.
The builtin run method now takes the
SERVER_NAMEinto account when picking the default port to run on.
flask.request.get_json()as a replacement for the old
Released 2012-07-01, 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 environ
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 wide,
flask.get_flashed_messages()function now allows rendering flashed message categories in separate blocks, through a
flask.Flask.run()method now accepts
portarguments, 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 instance of
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_fileand static files can be configured through a new
SEND_FILE_MAX_AGE_DEFAULTconfiguration variable, which is used in the default
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.
required_methodsattribute 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.
Fixed an issue with the undocumented
flask.sessionmodule to not work properly on Python 2.5. It should not be used but did cause some problems for package managers.
Released 2011-09-29, 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.
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
getmethod 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.
Fixed the Jinja2 environment’s
list_templatesmethod not returning the correct names when blueprints or modules were involved.
Fixed an issue with URL processors not properly working on blueprints.
Added missing future import that broke 2.5 compatibility.
Fixed an infinite redirect issue with blueprints.
Released 2011-06-28, codename Grappa
make_default_options_response()which can be used by subclasses to alter the default behavior for
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 warnings.
Fixed a problem for Flask to run on jython.
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_rulefunction and can now also accept regular werkzeug rules added to the url map.
endpointmethod 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.
create_jinja_loaderto override the loader creation process.
Implemented a silent flag for
teardown_requestdecorator, for functions that should run at the end of a request regardless of whether an exception occurred. Also the behavior for
after_requestwas changed. It’s now no longer executed when an exception is raised.
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_requesthandlers 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 class-based views.
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 2010-07-27, 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
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
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.
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.
Fixed another issue with loading templates from directories when modules were used.
Fixes an issue with template loading from directories when modules where used.
Released 2010-07-06, 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_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_loaderwhich is no longer used in 0.5 due to the improved module support.
Added a helper function to expose files from any directory.
Released 2010-06-18, 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.
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 2010-05-28, 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 2010-05-12, codename J?germeister
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.