The Falcon Web Framework
Falcon is a reliable, high-performance Python web framework for building large-scale app backends and microservices. It encourages the REST architectural style, and tries to do as little as possible while remaining highly effective.
Falcon apps work with any WSGI or ASGI server, and run like a champ under CPython 3.5+ and PyPy 3.5+ (3.6+ required for ASGI).
A Big Thank You to Our Patrons
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Learn how to support Falcon development
Thanks!
Quick Links
- Read the docs
- Falcon add-ons and complementary packages
- Falcon talks, podcasts, and blog posts
- falconry/user for Falcon users @ Gitter
- falconry/dev for Falcon contributors @ Gitter
What People are Saying
"We have been using Falcon as a replacement for [framework] and we simply love the performance (three times faster) and code base size (easily half of our original [framework] code)."
"Falcon looks great so far. I hacked together a quick test for a tiny server of mine and was ~40% faster with only 20 minutes of work."
"Falcon is rock solid and it's fast."
"I'm loving #falconframework! Super clean and simple, I finally have the speed and flexibility I need!"
"I feel like I'm just talking HTTP at last, with nothing in the middle. Falcon seems like the requests of backend."
"The source code for Falcon is so good, I almost prefer it to documentation. It basically can't be wrong."
"What other framework has integrated support for 786 TRY IT NOW ?"
Features
- ASGI and WSGI Support
- WebSocket Support
- Native asyncio support (no hacks or compatibility layers)
- Strict adherence to RFCs
- Highly-optimized, extensible code base
- Intuitive routing via URI templates and REST-inspired resource classes
- No reliance on magic globals for routing and state management
- Easy access to headers and bodies through request and response classes
- DRY request processing via middleware components and hooks
- Idiomatic HTTP error responses
- Straightforward exception handling
- Snappy testing through WSGI/ASGI helpers and mocks
- CPython 3.5+ and PyPy 3.5+ support
- ~20% speed boost under CPython when Cython is available
How is Falcon Different?
Perfection is finally attained not when there is no longer anything to add, but when there is no longer anything to take away.
- Antoine de Saint-ExupΓ©ry
We designed Falcon to support the demanding needs of large-scale microservices and responsive app backends. Falcon complements more general Python web frameworks by providing bare-metal performance, reliability, and flexibility wherever you need it.
Fast. Same hardware, more requests. Falcon turns around requests several times faster than most other Python frameworks. For an extra speed boost, Falcon compiles itself with Cython when available, and also works well with PyPy. Considering a move to another programming language? Benchmark with Falcon + PyPy first.
Reliable. We go to great lengths to avoid introducing breaking changes, and when we do they are fully documented and only introduced (in the spirit of SemVer) with a major version increment. The code is rigorously tested with numerous inputs and we require 100% coverage at all times. Falcon does not depend on any external Python packages.
Debuggable. Falcon eschews magic. It's easy to tell which inputs lead to which outputs. To avoid incentivizing the use of hard-to-debug global state, Falcon does not use decorators to define routes. Unhandled exceptions are never encapsulated or masked. Potentially surprising behaviors, such as automatic request body parsing, are well-documented and disabled by default. Finally, we take care to keep logic paths within the framework simple, shallow and understandable. All of this makes it easier to reason about the code and to debug edge cases in large-scale deployments.
Flexible. Falcon leaves a lot of decisions and implementation details to you, the API developer. This gives you a lot of freedom to customize and tune your implementation. Due to Falcon's minimalist design, Python community members are free to independently innovate on Falcon add-ons and complementary packages.
Who's Using Falcon?
Falcon is used around the world by a growing number of organizations, including:
- 7ideas
- Cronitor
- EMC
- Hurricane Electric
- Leadpages
- OpenStack
- Rackspace
- Shiftgig
- tempfil.es
- Opera Software
If you are using the Falcon framework for a community or commercial project, please consider adding your information to our wiki under Who's Using Falcon?
Community
A number of Falcon add-ons, templates, and complementary packages are available for use in your projects. We've listed several of these on the Falcon wiki as a starting point, but you may also wish to search PyPI for additional resources.
The Falconry community on Gitter is a great place to ask questions and share your ideas. You can find us in falconry/user. We also have a falconry/dev room for discussing the design and development of the framework itself.
Per our Code of Conduct, we expect everyone who participates in community discussions to act professionally, and lead by example in encouraging constructive discussions. Each individual in the community is responsible for creating a positive, constructive, and productive culture.
Installation
PyPy
PyPy is the fastest way to run your Falcon app. PyPy3.5+ is supported as of PyPy v5.10.
$ pip install falcon
Or, to install the latest beta or release candidate, if any:
$ pip install --pre falcon
CPython
Falcon also fully supports CPython 3.5+.
The latest stable version of Falcon can be installed directly from PyPI:
$ pip install falcon
Or, to install the latest beta or release candidate, if any:
$ pip install --pre falcon
In order to provide an extra speed boost, Falcon can compile itself with Cython. Wheels containing pre-compiled binaries are available from PyPI for several common platforms. However, if a wheel for your platform of choice is not available, you can choose to stick with the source distribution, or use the instructions below to cythonize Falcon for your environment.
The following commands tell pip to install Cython, and then to invoke Falcon's setup.py
, which will in turn detect the presence of Cython and then compile (AKA cythonize) the Falcon framework with the system's default C compiler.
$ pip install cython
$ pip install --no-build-isolation --no-binary :all: falcon
Note that --no-build-isolation
is necessary to override pip's default PEP 517 behavior that can cause Cython not to be found in the build environment.
If you want to verify that Cython is being invoked, simply pass -v to pip in order to echo the compilation commands:
$ pip install -v --no-build-isolation --no-binary :all: falcon
Installing on OS X
Xcode Command Line Tools are required to compile Cython. Install them with this command:
$ xcode-select --install
The Clang compiler treats unrecognized command-line options as errors, for example:
clang: error: unknown argument: '-mno-fused-madd' [-Wunused-command-line-argument-hard-error-in-future]
You might also see warnings about unused functions. You can work around these issues by setting additional Clang C compiler flags as follows:
$ export CFLAGS="-Qunused-arguments -Wno-unused-function"
Dependencies
Falcon does not require the installation of any other packages, although if Cython has been installed into the environment, it will be used to optimize the framework as explained above.
WSGI Server
Falcon speaks WSGI (or ASGI; see also below). In order to serve a Falcon app, you will need a WSGI server. Gunicorn and uWSGI are some of the more popular ones out there, but anything that can load a WSGI app will do.
$ pip install [gunicorn|uwsgi]
ASGI Server
In order to serve a Falcon ASGI app, you will need an ASGI server. Uvicorn is a popular choice:
$ pip install uvicorn
Source Code
Falcon lives on GitHub, making the code easy to browse, download, fork, etc. Pull requests are always welcome! Also, please remember to star the project if it makes you happy. :)
Once you have cloned the repo or downloaded a tarball from GitHub, you can install Falcon like this:
$ cd falcon
$ pip install .
Or, if you want to edit the code, first fork the main repo, clone the fork to your desktop, and then run the following to install it using symbolic linking, so that when you change your code, the changes will be automagically available to your app without having to reinstall the package:
$ cd falcon
$ pip install --no-use-pep517 -e .
You can manually test changes to the Falcon framework by switching to the directory of the cloned repo and then running pytest:
$ cd falcon
$ pip install -r requirements/tests
$ pytest tests
Or, to run the default set of tests:
$ pip install tox && tox
See also the tox.ini file for a full list of available environments.
Read the Docs
The docstrings in the Falcon code base are quite extensive, and we recommend keeping a REPL running while learning the framework so that you can query the various modules and classes as you have questions.
Online docs are available at: https://falcon.readthedocs.io
You can build the same docs locally as follows:
$ pip install tox && tox -e docs
Once the docs have been built, you can view them by opening the following index page in your browser. On OS X it's as simple as:
$ open docs/_build/html/index.html
Or on Linux:
$ xdg-open docs/_build/html/index.html
Getting Started
Here is a simple, contrived example showing how to create a Falcon-based WSGI app (the ASGI version is included further down):
# examples/things.py
# Let's get this party started!
from wsgiref.simple_server import make_server
import falcon
# Falcon follows the REST architectural style, meaning (among
# other things) that you think in terms of resources and state
# transitions, which map to HTTP verbs.
class ThingsResource:
def on_get(self, req, resp):
"""Handles GET requests"""
resp.status = falcon.HTTP_200 # This is the default status
resp.content_type = falcon.MEDIA_TEXT # Default is JSON, so override
resp.text = ('\nTwo things awe me most, the starry sky '
'above me and the moral law within me.\n'
'\n'
' ~ Immanuel Kant\n\n')
# falcon.App instances are callable WSGI apps...
# in larger applications the app is created in a separate file
app = falcon.App()
# Resources are represented by long-lived class instances
things = ThingsResource()
# things will handle all requests to the '/things' URL path
app.add_route('/things', things)
if __name__ == '__main__':
with make_server('', 8000, app) as httpd:
print('Serving on port 8000...')
# Serve until process is killed
httpd.serve_forever()
You can run the above example directly using the included wsgiref server:
$ pip install falcon
$ python things.py
Then, in another terminal:
$ curl localhost:8000/things
The ASGI version of the example is similar:
# examples/things_asgi.py
import falcon
import falcon.asgi
# Falcon follows the REST architectural style, meaning (among
# other things) that you think in terms of resources and state
# transitions, which map to HTTP verbs.
class ThingsResource:
async def on_get(self, req, resp):
"""Handles GET requests"""
resp.status = falcon.HTTP_200 # This is the default status
resp.content_type = falcon.MEDIA_TEXT # Default is JSON, so override
resp.text = ('\nTwo things awe me most, the starry sky '
'above me and the moral law within me.\n'
'\n'
' ~ Immanuel Kant\n\n')
# falcon.asgi.App instances are callable ASGI apps...
# in larger applications the app is created in a separate file
app = falcon.asgi.App()
# Resources are represented by long-lived class instances
things = ThingsResource()
# things will handle all requests to the '/things' URL path
app.add_route('/things', things)
You can run the ASGI version with uvicorn or any other ASGI server:
$ pip install falcon uvicorn
$ uvicorn things_asgi:app
A More Complex Example (WSGI)
Here is a more involved example that demonstrates reading headers and query parameters, handling errors, and working with request and response bodies. Note that this example assumes that the requests package has been installed.
(For the equivalent ASGI app, see: A More Complex Example (ASGI)).
# examples/things_advanced.py
import json
import logging
import uuid
from wsgiref import simple_server
import falcon
import requests
class StorageEngine:
def get_things(self, marker, limit):
return [{'id': str(uuid.uuid4()), 'color': 'green'}]
def add_thing(self, thing):
thing['id'] = str(uuid.uuid4())
return thing
class StorageError(Exception):
@staticmethod
def handle(ex, req, resp, params):
# TODO: Log the error, clean up, etc. before raising
raise falcon.HTTPInternalServerError()
class SinkAdapter:
engines = {
'ddg': 'https://duckduckgo.com',
'y': 'https://search.yahoo.com/search',
}
def __call__(self, req, resp, engine):
url = self.engines[engine]
params = {'q': req.get_param('q', True)}
result = requests.get(url, params=params)
resp.status = str(result.status_code) + ' ' + result.reason
resp.content_type = result.headers['content-type']
resp.text = result.text
class AuthMiddleware:
def process_request(self, req, resp):
token = req.get_header('Authorization')
account_id = req.get_header('Account-ID')
challenges = ['Token type="Fernet"']
if token is None:
description = ('Please provide an auth token '
'as part of the request.')
raise falcon.HTTPUnauthorized(title='Auth token required',
description=description,
challenges=challenges,
href='http://docs.example.com/auth')
if not self._token_is_valid(token, account_id):
description = ('The provided auth token is not valid. '
'Please request a new token and try again.')
raise falcon.HTTPUnauthorized(title='Authentication required',
description=description,
challenges=challenges,
href='http://docs.example.com/auth')
def _token_is_valid(self, token, account_id):
return True # Suuuuuure it's valid...
class RequireJSON:
def process_request(self, req, resp):
if not req.client_accepts_json:
raise falcon.HTTPNotAcceptable(
description='This API only supports responses encoded as JSON.',
href='http://docs.examples.com/api/json')
if req.method in ('POST', 'PUT'):
if 'application/json' not in req.content_type:
raise falcon.HTTPUnsupportedMediaType(
title='This API only supports requests encoded as JSON.',
href='http://docs.examples.com/api/json')
class JSONTranslator:
# NOTE: Normally you would simply use req.media and resp.media for
# this particular use case; this example serves only to illustrate
# what is possible.
def process_request(self, req, resp):
# req.stream corresponds to the WSGI wsgi.input environ variable,
# and allows you to read bytes from the request body.
#
# See also: PEP 3333
if req.content_length in (None, 0):
# Nothing to do
return
body = req.stream.read()
if not body:
raise falcon.HTTPBadRequest(title='Empty request body',
description='A valid JSON document is required.')
try:
req.context.doc = json.loads(body.decode('utf-8'))
except (ValueError, UnicodeDecodeError):
description = ('Could not decode the request body. The '
'JSON was incorrect or not encoded as '
'UTF-8.')
raise falcon.HTTPBadRequest(title='Malformed JSON',
description=description)
def process_response(self, req, resp, resource, req_succeeded):
if not hasattr(resp.context, 'result'):
return
resp.text = json.dumps(resp.context.result)
def max_body(limit):
def hook(req, resp, resource, params):
length = req.content_length
if length is not None and length > limit:
msg = ('The size of the request is too large. The body must not '
'exceed ' + str(limit) + ' bytes in length.')
raise falcon.HTTPPayloadTooLarge(
title='Request body is too large', description=msg)
return hook
class ThingsResource:
def __init__(self, db):
self.db = db
self.logger = logging.getLogger('thingsapp.' + __name__)
def on_get(self, req, resp, user_id):
marker = req.get_param('marker') or ''
limit = req.get_param_as_int('limit') or 50
try:
result = self.db.get_things(marker, limit)
except Exception as ex:
self.logger.error(ex)
description = ('Aliens have attacked our base! We will '
'be back as soon as we fight them off. '
'We appreciate your patience.')
raise falcon.HTTPServiceUnavailable(
title='Service Outage',
description=description,
retry_after=30)
# NOTE: Normally you would use resp.media for this sort of thing;
# this example serves only to demonstrate how the context can be
# used to pass arbitrary values between middleware components,
# hooks, and resources.
resp.context.result = result
resp.set_header('Powered-By', 'Falcon')
resp.status = falcon.HTTP_200
@falcon.before(max_body(64 * 1024))
def on_post(self, req, resp, user_id):
try:
doc = req.context.doc
except AttributeError:
raise falcon.HTTPBadRequest(
title='Missing thing',
description='A thing must be submitted in the request body.')
proper_thing = self.db.add_thing(doc)
resp.status = falcon.HTTP_201
resp.location = '/%s/things/%s' % (user_id, proper_thing['id'])
# Configure your WSGI server to load "things.app" (app is a WSGI callable)
app = falcon.App(middleware=[
AuthMiddleware(),
RequireJSON(),
JSONTranslator(),
])
db = StorageEngine()
things = ThingsResource(db)
app.add_route('/{user_id}/things', things)
# If a responder ever raises an instance of StorageError, pass control to
# the given handler.
app.add_error_handler(StorageError, StorageError.handle)
# Proxy some things to another service; this example shows how you might
# send parts of an API off to a legacy system that hasn't been upgraded
# yet, or perhaps is a single cluster that all data centers have to share.
sink = SinkAdapter()
app.add_sink(sink, r'/search/(?P<engine>ddg|y)\Z')
# Useful for debugging problems in your API; works with pdb.set_trace(). You
# can also use Gunicorn to host your app. Gunicorn can be configured to
# auto-restart workers when it detects a code change, and it also works
# with pdb.
if __name__ == '__main__':
httpd = simple_server.make_server('127.0.0.1', 8000, app)
httpd.serve_forever()
Again this code uses wsgiref, but you can also run the above example using any WSGI server, such as uWSGI or Gunicorn. For example:
$ pip install requests gunicorn
$ gunicorn things:app
On Windows you can run Gunicorn and uWSGI via WSL, or you might try Waitress:
$ pip install requests waitress
$ waitress-serve --port=8000 things:app
To test this example, open another terminal and run:
$ http localhost:8000/1/things authorization:custom-token
You can also view the the application configuration from the CLI via the falcon-inspect-app
script that is bundled with the framework:
falcon-inspect-app things_advanced:app
A More Complex Example (ASGI)
Here's the ASGI version of the app from above. Note that it uses the httpx package in lieu of requests.
# examples/things_advanced_asgi.py
import json
import logging
import uuid
import falcon
import falcon.asgi
import httpx
class StorageEngine:
async def get_things(self, marker, limit):
return [{'id': str(uuid.uuid4()), 'color': 'green'}]
async def add_thing(self, thing):
thing['id'] = str(uuid.uuid4())
return thing
class StorageError(Exception):
@staticmethod
async def handle(ex, req, resp, params):
# TODO: Log the error, clean up, etc. before raising
raise falcon.HTTPInternalServerError()
class SinkAdapter:
engines = {
'ddg': 'https://duckduckgo.com',
'y': 'https://search.yahoo.com/search',
}
async def __call__(self, req, resp, engine):
url = self.engines[engine]
params = {'q': req.get_param('q', True)}
async with httpx.AsyncClient() as client:
result = await client.get(url, params=params)
resp.status = result.status_code
resp.content_type = result.headers['content-type']
resp.text = result.text
class AuthMiddleware:
async def process_request(self, req, resp):
token = req.get_header('Authorization')
account_id = req.get_header('Account-ID')
challenges = ['Token type="Fernet"']
if token is None:
description = ('Please provide an auth token '
'as part of the request.')
raise falcon.HTTPUnauthorized(title='Auth token required',
description=description,
challenges=challenges,
href='http://docs.example.com/auth')
if not self._token_is_valid(token, account_id):
description = ('The provided auth token is not valid. '
'Please request a new token and try again.')
raise falcon.HTTPUnauthorized(title='Authentication required',
description=description,
challenges=challenges,
href='http://docs.example.com/auth')
def _token_is_valid(self, token, account_id):
return True # Suuuuuure it's valid...
class RequireJSON:
async def process_request(self, req, resp):
if not req.client_accepts_json:
raise falcon.HTTPNotAcceptable(
description='This API only supports responses encoded as JSON.',
href='http://docs.examples.com/api/json')
if req.method in ('POST', 'PUT'):
if 'application/json' not in req.content_type:
raise falcon.HTTPUnsupportedMediaType(
description='This API only supports requests encoded as JSON.',
href='http://docs.examples.com/api/json')
class JSONTranslator:
# NOTE: Normally you would simply use req.get_media() and resp.media for
# this particular use case; this example serves only to illustrate
# what is possible.
async def process_request(self, req, resp):
# NOTE: Test explicitly for 0, since this property could be None in
# the case that the Content-Length header is missing (in which case we
# can't know if there is a body without actually attempting to read
# it from the request stream.)
if req.content_length == 0:
# Nothing to do
return
body = await req.stream.read()
if not body:
raise falcon.HTTPBadRequest(title='Empty request body',
description='A valid JSON document is required.')
try:
req.context.doc = json.loads(body.decode('utf-8'))
except (ValueError, UnicodeDecodeError):
description = ('Could not decode the request body. The '
'JSON was incorrect or not encoded as '
'UTF-8.')
raise falcon.HTTPBadRequest(title='Malformed JSON',
description=description)
async def process_response(self, req, resp, resource, req_succeeded):
if not hasattr(resp.context, 'result'):
return
resp.text = json.dumps(resp.context.result)
def max_body(limit):
async def hook(req, resp, resource, params):
length = req.content_length
if length is not None and length > limit:
msg = ('The size of the request is too large. The body must not '
'exceed ' + str(limit) + ' bytes in length.')
raise falcon.HTTPPayloadTooLarge(
title='Request body is too large', description=msg)
return hook
class ThingsResource:
def __init__(self, db):
self.db = db
self.logger = logging.getLogger('thingsapp.' + __name__)
async def on_get(self, req, resp, user_id):
marker = req.get_param('marker') or ''
limit = req.get_param_as_int('limit') or 50
try:
result = await self.db.get_things(marker, limit)
except Exception as ex:
self.logger.error(ex)
description = ('Aliens have attacked our base! We will '
'be back as soon as we fight them off. '
'We appreciate your patience.')
raise falcon.HTTPServiceUnavailable(
title='Service Outage',
description=description,
retry_after=30)
# NOTE: Normally you would use resp.media for this sort of thing;
# this example serves only to demonstrate how the context can be
# used to pass arbitrary values between middleware components,
# hooks, and resources.
resp.context.result = result
resp.set_header('Powered-By', 'Falcon')
resp.status = falcon.HTTP_200
@falcon.before(max_body(64 * 1024))
async def on_post(self, req, resp, user_id):
try:
doc = req.context.doc
except AttributeError:
raise falcon.HTTPBadRequest(
title='Missing thing',
description='A thing must be submitted in the request body.')
proper_thing = await self.db.add_thing(doc)
resp.status = falcon.HTTP_201
resp.location = '/%s/things/%s' % (user_id, proper_thing['id'])
# The app instance is an ASGI callable
app = falcon.asgi.App(middleware=[
# AuthMiddleware(),
RequireJSON(),
JSONTranslator(),
])
db = StorageEngine()
things = ThingsResource(db)
app.add_route('/{user_id}/things', things)
# If a responder ever raises an instance of StorageError, pass control to
# the given handler.
app.add_error_handler(StorageError, StorageError.handle)
# Proxy some things to another service; this example shows how you might
# send parts of an API off to a legacy system that hasn't been upgraded
# yet, or perhaps is a single cluster that all data centers have to share.
sink = SinkAdapter()
app.add_sink(sink, r'/search/(?P<engine>ddg|y)\Z')
You can run the ASGI version with any ASGI server, such as uvicorn:
$ pip install falcon httpx uvicorn
$ uvicorn things_advanced_asgi:app
Contributing
Thanks for your interest in the project! We welcome pull requests from developers of all skill levels. To get started, simply fork the master branch on GitHub to your personal account and then clone the fork into your development environment.
If you would like to contribute but don't already have something in mind, we invite you to take a look at the issues listed under our next milestone. If you see one you'd like to work on, please leave a quick comment so that we don't end up with duplicated effort. Thanks in advance!
Please note that all contributors and maintainers of this project are subject to our Code of Conduct.
Before submitting a pull request, please ensure you have added/updated the appropriate tests (and that all existing tests still pass with your changes), and that your coding style follows PEP 8 and doesn't cause pyflakes to complain.
Commit messages should be formatted using AngularJS conventions.
Comments follow Google's style guide, with the additional requirement of prefixing inline comments using your GitHub nick and an appropriate prefix:
- TODO(riker): Damage report!
- NOTE(riker): Well, that's certainly good to know.
- PERF(riker): Travel time to the nearest starbase?
- APPSEC(riker): In all trust, there is the possibility for betrayal.
The core Falcon project maintainers are:
- Kurt Griffiths, Project Lead (kgriffs on GH, Gitter, and Twitter)
- John Vrbanac (jmvrbanac on GH, Gitter, and Twitter)
- Vytautas Liuolia (vytas7 on GH and Gitter, and vliuolia on Twitter)
- Nick Zaccardi (nZac on GH and Gitter)
Please don't hesitate to reach out if you have any questions, or just need a little help getting started. You can find us in falconry/dev on Gitter.
See also: CONTRIBUTING.md
Legal
Copyright 2013-2020 by Individual and corporate contributors as noted in the individual source files.
Falcon image courtesy of John O'Neill.
Licensed under the Apache License, Version 2.0 (the "License"); you may not use any portion of the Falcon framework except in compliance with the License. Contributors agree to license their work under the same License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.