Released on May 2nd 2018
- Fix more backwards compatibility issues with merging slashes between
a blueprint prefix and route. (#2748)
- Fix error with
flask routes command when there are no routes.
Released on April 29th 2018
- Fix registering partials (with no
__name__) as view functions.
- Don’t treat lists returned from view functions the same as tuples.
Only tuples are interpreted as response data. (#2736)
- Extra slashes between a blueprint’s
url_prefix and a route URL
are merged. This fixes some backwards compatibility issues with the
change in 1.0. (#2731, #2742)
- Only trap
BadRequestKeyError errors in debug mode, not all
BadRequest errors. This allows
abort(400) to continue
working as expected. (#2735)
FLASK_SKIP_DOTENV environment variable can be set to
to skip automatically loading dotenv files. (#2722)
Released on April 26th 2018
- Python 2.6 and 3.3 are no longer supported. (pallets/meta#24)
- Bump minimum dependency versions to the latest stable versions:
Werkzeug >= 0.14, Jinja >= 2.10, itsdangerous >= 0.24, Click >= 5.1.
app.run when a Flask application is run
from the command line. This avoids some behavior that was confusing
- Change the default for
jsonify() returns a compact format by
default, and an indented format in debug mode. (#2193)
Flask.__init__ accepts the
argument and sets it on
Flask.__init__ accepts the
and passes it as the
host argument when defining the static
send_file() supports Unicode in
_scheme argument from
add_url_rule() accepts the
provide_automatic_options argument to disable adding the
OPTIONS method. (#1489)
MethodView subclasses inherit method handlers from
base classes. (#1936)
- Errors caused while opening the session at the beginning of the
request are handled by the app’s error handlers. (#2254)
- Blueprints gained
json_decoder attributes to override the app’s
encoder and decoder. (#1898)
TypeError instead of
ValueError for bad response types. The error messages have been
improved to describe why the type is invalid. (#2256)
routes CLI command to output routes registered on the
- 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
- Allow IP address as exact session cookie domain. (#2282)
SESSION_COOKIE_DOMAIN is set if it is detected through
- Auto-detect zero-argument app factory called
- Factory functions are not required to take a
parameter to work with the
flask command. If they take a single
parameter or a parameter named
ScriptInfo object will be passed. (#2319)
FLASK_APP can be set to an app factory, with arguments if
needed, for example
FLASK_APP can point to local packages that are not installed in
editable mode, although
pip install -e is still preferred.
View class attribute
provide_automatic_options is set in
as_view(), to be detected by
- Error handling will try handlers registered for
Cookie is added to the response’s
Vary header if the session
is accessed at all during the request (and not deleted). (#2288)
url_scheme arguments for use when building the base URL.
'/' by default. This was already
the implicit default when it was set to
TRAP_BAD_REQUEST_ERRORS is enabled by default in debug mode.
BadRequestKeyError has a message with the bad key in debug mode
instead of the generic bad request message. (#2348)
- Allow registering new tags with
TaggedJSONSerializer to support storing other
types in the session cookie. (#2352)
- Only open the session if the request has not been pushed onto the
context stack yet. This allows
generators to access the same session that the containing view uses.
json keyword argument for the test client request methods.
This will dump the given object as JSON and set the appropriate
content type. (#2358)
- Extract JSON handling to a mixin applied to both the
Response classes. This adds the
get_json() methods to
the response to make testing JSON response much easier. (#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
- Fix incorrect JSON encoding of aware, non-UTC datetimes. (#2374)
- Template auto reloading will honor debug mode even even if
jinja_env was already accessed. (#2373)
- The following old deprecated code was removed. (#2385)
Request.json property is no longer deprecated.
- Support passing a
flask command and
Flask.run() will load environment
.flaskenv files if python-dotenv is
- When passing a full URL to the test client, the scheme in the URL is
used instead of
Flask.logger has been simplified.
LOGGER_HANDLER_POLICY config was removed. The logger is always
flask.app. The level is only set on first access, it
Flask.debug each time. Only one format is
used, not different ones depending on
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)
- Fix a
ValueError caused by invalid
Range requests in some
- The development server uses threads by default. (#2529)
- Loading config files with
silent=True will ignore
ENOTDIR errors. (#2581)
--key options to
flask run to run the
development server over HTTPS. (#2606)
SESSION_COOKIE_SAMESITE to control the
attribute on the session cookie. (#2607)
test_cli_runner() to create a Click runner
that can invoke Flask CLI commands for testing. (#2636)
- Subdomain matching is disabled by default and setting
SERVER_NAME does not implicily enable it. It can be enabled
subdomain_matching=True to the
- A single trailing slash is stripped from the blueprint
url_prefix when it is registered with the app. (#2629)
Request.get_json() doesn’t cache the
result if parsing fails when
silent is true. (#2651)
Request.get_json() no longer accepts arbitrary encodings.
Incoming JSON should be encoded using UTF-8 per RFC 8259, but
Flask will autodetect UTF-8, -16, or -32. (#2691)
to control when Werkzeug warns about large cookies that browsers may
- Updated documentation theme to make docs look better in small
- Rewrote the tutorial docs and example project to take a more
structured approach to help new users avoid common pitfalls.
Released on April 29 2018
- Repackage 0.12.3 to fix package layout issue. (#2728)
Released on April 26th 2018
Request.get_json() no longer accepts arbitrary encodings.
Incoming JSON should be encoded using UTF-8 per RFC 8259, but
Flask will autodetect UTF-8, -16, or -32. (#2692)
- Fix a Python warning about imports when using
python -m flask.
- Fix a
ValueError caused by invalid
Range requests in some
Released on May 16 2017
- Fix a bug in safe_join on Windows.
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_pyfile for Python 3. Fix
- Use the
SERVER_NAME config 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
Released on December 21st 2016, codename Punsch.
- the cli command now responds to –version.
- Mimetype guessing and ETag generation for file-like objects in
has been removed, as per issue
#104. See pull request
- Mimetype guessing in
send_file now fails loudly and doesn’t fall back to
application/octet-stream. See pull request
flask.safe_join able 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_client includes 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__.py from working. See
Released on May 29th 2016, codename Absinthe.
- Added support to serializing top-level arrays to
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_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
from a view function.
- 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
- Added flask 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
- 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
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
- Ported test suite to py.test.
request.json in 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
OPTIONS method is now correctly disabled if
the user registered an overriding rule with the lowercase-version
flask.json.jsonify now supports the
datetime.date type (pull request
- Don’t leak exception info of already catched exceptions to context teardown
handlers (pull request
- Allow custom Jinja environment subclasses (pull request
- Updated extension dev guidelines.
flask.g now has
- Turn on autoescape for
flask.templating.render_template_string by default
flask.ext is now deprecated (pull request
send_from_directory now raises BadRequest if the filename is invalid on
the server OS (pull request
- Added the
JSONIFY_MIMETYPE configuration 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
- 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
|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 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_test methods in addition to the already existing
template_filter method family.
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
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.
flask.Request.on_json_loading_failed() now returns a JSON formatted
response by default.
flask.url_for() function now can generate anchors to 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
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
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,
flask.get_flashed_messages() function now allows rendering flashed
message categories in separate blocks, through a
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.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"), 400 from a view function.
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
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.
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
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. (
- 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
APPLICATION_ROOT configuration variable.
easily modify sessions from the test environment.
- Refactored test client internally. The
variable as well as
SERVER_NAME are now properly used by the test client
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
which can be used by subclasses to alter the default
- Unbound locals now raise a proper
- 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
- 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
- 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
- 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
- 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
- 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
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
MAX_CONTENT_LENGTH configuration value.
- the endpoint for the
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
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
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
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.
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
- 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
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
- 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.