Python Feature Flags

Python Feature Flag Resources/Solutions

  • LaunchDarkly Python Feature Flag SDK – LaunchDarkly
    • An installable feature flag software development kit for Python apps.  This SDK harnesses the LaunchDarkly app and allows you to target users and manage rollouts.  Feature flags are evaluated in microseconds.
    • Main Website
    • GitHub Repo
  • Flask Feature Flags – Rachel Sanders
    • “This is a Flask extension that adds feature flagging to your applications. This lets you turn parts of your site on or off based on configuration. It’s useful for any setup where you deploy from trunk but want to hide unfinished features from your users, such as continuous integration builds. You can also extend it to do simple a/b testing or whitelisting.”
    • GitHub Repo
  • Disqus Gutter – Disqus
    • “This repo is the client for Gargoyle 2, known as “Gutter”. It does not work with the existing Gargoyle 1 codebase. Gutter is feature switch management library. It allows users to create feature switches and setup conditions those switches will be enabled for. Once configured, switches can then be checked against inputs (requests, user objects, etc) to see if the switches are active.  For a UI to configure Gutter with see the gutter-django project.”
    • GitHub Repo
  • Forrst – Zurb
    • Discussion regarding feature flags for python
    • GitHub Repo
  • Flagon – Stephen Milner
    • “Generic feature flags for python which attempts to be compatible with Java’s Togglz ( A simple flag status api is provided under flagon.status_api. Example wsgi file can be found in contrib/wsgi. The status api requires werkzeug.”
    • GitHub Repo
  • Feature Ramp – Amanda Schloss and Anthony Yim
    • “Toggling and ramping features via a lightweight Redis backend.”
    • GitHub Repo


LaunchDarkly Python SDK Reference

This reference guide documents all of the methods available in LaunchDarkly’s Python SDK, and explains in detail how these methods work. If you want to dig even deeper, LaunchDarkly’s SDKs are open source– head to the Python SDK GitHub repository to look under the hood.

Getting started

If you haven’t taken a look at our Quickstart guide yet, we recommend starting there to see how install our SDK into your Python application.

Once the SDK is installed, you’ll want to configure the LaunchDarkly client:

ldclient.sdk_key = "YOUR_SDK_KEY"

Customizing your client

You can also pass custom parameters to the client by creating a custom configuration object:

ldclient.config = Config('', 1, 2)

The Config allows you to specify a custom base URL (you probably don’t need to do this), as well as customize timeout parameters. In this example, we’ve set the connection timeout to LaunchDarkly to 1 second, and the read timeout to 2 seconds.


Feature flag targeting and rollouts are all determined by the user you pass to your Variation calls. In our Python SDK, users are simply dictionaries. Here’s an example:

user = {
  "key": "aa0ceb",
  "firstName": "Ernestina",
  "lastName": "Evans",
  "email": "",
  "custom": {
    "groups": ["Google", "Microsoft"]

Let’s walk through this snippet. The most important attribute is the user key– in this case we’ve used the hash"aa0ceb". The user key is the only mandatory user attribute. The key should also uniquely identify each user. You can use a primary key, an e-mail address, or a hash, as long as the same user always has the same key. We recommend using a hash if possible.

All of the other attributes (like firstName, email, and the custom attributes) are optional. The attributes you specify will automatically appear on our dashboard, meaning that you can start segmenting and targeting users with these attributes.

Besides the key, LaunchDarkly supports the following attributes at the “top level”. Remember, all of these are optional:

  • ip: Must be an IP address. If you provide an IP, LaunchDarkly will use a geolocation service to automatically infer a country for the user (unless you’ve already specified one).
  • firstName: Must be a string. If you provide a first name, you can search for users on the Users page by name.
  • lastName: Must be a string. If you provide a last name, you can search for users on the Users page by name.
  • country: Must be a string representing the country associated with the user.
  • email: Must be a string representing the user’s e-mail address. If an avatar URL is not provided, we’ll useGravatar to try to display an avatar for the user on the Users page.
  • avatar: Must be an absolute URL to an avatar image for the user.
  • name: Must be a string. You can search for users on the User page by name
  • anonymous: Must be a boolean. See the section below on anonymous users for more details.

In addition to built-in attributes, you can pass us any of your own user data by passing custom attributes, like thegroups attribute in the example above.

A note on types

Most of our built-in attributes (like names and e-mail addresses) expect string values. Custom attribute values can be strings, booleans (like True or False), numbers, or lists of strings, booleans or numbers.

If you enter a custom value on our dashboard that looks like a number or a boolean, it’ll be interpreted that way.

Custom attributes are one of the most powerful features of LaunchDarkly. They let you target users according to any data that you want to send to us– organizations, groups, account plans– anything you pass to us becomes available instantly on our dashboard.

Anonymous users

You can also distinguish logged-in users from anonymous users in the SDK, as follows:

user = {"key":"aa0ceb", "anonymous": True}

You will still need to generate a unique key for anonymous users– session IDs or UUIDs work best for this.

Anonymous users work just like regular users, except that they won’t appear on your Users page in LaunchDarkly. You also can’t search for anonymous users on your Features page, and you can’t search or autocomplete by anonymous user keys. This is actually a good thing– it keeps anonymous users from polluting your Users page!


The variation method determines which variation of a feature flag a user receives.

ldclient.get().variation("your.feature.key", user, False)

variation calls take the feature flag key, an LDUser, and a default value.

The default value will only be returned if an error is encountered– for example, if the feature flag key doesn’t exist or the user doesn’t have a key specified.

The variation call will automatically create a user in LaunchDarkly if a user with that user key doesn’t exist already. There’s no need to create users ahead of time (but if you do need to, take a look at Identify).

All Flags

The all_flags method produces a dictionary of feature flag keys to their values for a specific user.

This method can be useful for passing feature flags to your front-end. In particular, it can be used to provide bootstrap flag settings for our JavaScript SDK.



The track method allows you to record actions your users take on your site. This lets you record events that take place on your server. In LaunchDarkly, you can tie these events to goals in A/B tests. Here’s a simple example:

ldclient.get().track("Signed up", user)

You can also attach an extra dictionary containing arbitrary data to your event:

ldclient.get().track("Completed purchase", {"price": 320})


The identify method creates or updates users on LaunchDarkly, making them available for targeting and autocomplete on the dashboard. In most cases, you won’t need to call identify— the variation call will automatically create users on the dashboard for you. identify can be useful if you want to pre-populate your dashboard before launching any features.


Secure mode hash

The SecureModeHash method computes an HMAC signature of a user signed with the client’s SDK key. If you’re using our JavaScript SDK for client-side flags, this method generates the signature you need for secure mode.


Offline mode

In some situations, you might want avoid remote calls to LaunchDarkly and fall back to default values for your feature flags. For example, if your software is both cloud-hosted and distributed to customers to run on premise, it might make sense to fall back to defaults when running on premise. You can do this by setting offline mode in the client’s Config.

# Initialization:
ldclient.config = Config(offline = True)
ldclient.sdk_key = "YOUR_SDK_KEY"

ldclient.get().variation("any.feature.flag", user, False) # will always return the default value (false)


Internally, the LaunchDarkly SDK keeps an event buffer for track and identify calls. These are flushed periodically in a background thread. In some situations (for example, if you’re testing out the SDK in a REPL), you may want to manually call flush to process events immediately.


Note that the flush interval is configurable– if you need to change the interval, you can do so when configuring your client instance.


Close safely shuts down the client instance and releases all resources associated with the client. In most long-running applications, you should not have to call close.


Configuring uWSGI

The LaunchDarkly SDK is compatible with uWSGI. However, in uWSGI environments, the SDK requires the enable-threads option to be set.