Feature Flagging for Flask
Feature Flagging for Flask
This library was heavily inspired by django-waffle.
$ python -m pip install flask-pancake Successfully installed flask-pancake
from flask import Flask from flask_pancake import FlaskPancake, Switch from flask_redis import FlaskRedis app = Flask(__name__) pancake = FlaskPancake(app) redis = FlaskRedis(app) SWITCH_FEATURE = Switch("FEATURE", default=False) @app.route("/") def index(): if SWITCH_FEATURE.is_active(): return "Hello World!", 200 else: return "Not found", 404
Alternatively, if you use a
create_app() method to configure your Flask app,
from flask import Flask from flask_pancake import FlaskPancake pancake = FlaskPancake() def create_app() -> Flask: app = Flask(__name__) pancake.init_app(app) return app
flask-pancake provides three types of flags:
Switches, which are either globally active or inactive. A common use case for these are system-wide enabling or disabling of a feature. E.g. in the context of a dependency on a third party service, disabling a feature with a global switch when that service is unavailable.
Flags are like Switches but can be overridden per user. To make use of Flags, one needs to define a function that returns a user's unique ID or
from flask import request from flask_pancake import FlaskPancake def get_user_id(): return getattr(getattr(request, "user", None), "uid", None) pancake = FlaskPancake(get_user_id_func=get_user_id) # Or, if importing a function from somewhere isn't possible, a string based # approach can be used. # Separate the the fully qualified module path from the function with a `:` pancake = FlaskPancake(get_user_id_func="my.app.account.utils:get_uid")
Samples, have a global "ratio" of 0 - 100%. Each time a check is done on a sample, a random value is checked within these bounds. Hence:
# DO THIS! def foo(): is_active = MY_SAMPLE.is_active() if is_active: # do something pass ... if is_active: # do more pass # DO NOT DO THIS! def foo(): if MY_SAMPLE.is_active(): # do something pass ... if MY_SAMPLE.is_active(): # do more pass
In the second example, each call to
is_active()will be evaluated again. Thus, the first block might be executed, but the second might not (or vice versa).
The persisted state for all three types of feature flags can be cleared, using
Similarly, one can change the persisted state for Flags and Switches using
enable() methods. Samples can be updated using their
set(value: float) method.
Flags, there are
to clear the state for the current or all users. Along the same line, there are
enable_user() to set the current user's state.
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