LaunchDarkly Python Server SDK

Warnings

• breaking Python 3.9 is no longer supported starting with version 9.15.0.
  Fix: Upgrade your Python environment to 3.10 or newer. If you must use Python 3.9, pin the SDK version to `<9.15.0` (e.g., `launchdarkly-server-sdk<9.15.0`).
• breaking Python 3.8 is no longer supported starting with version 9.12.0.
  Fix: Upgrade your Python environment to 3.9 or newer. If you must use Python 3.8, pin the SDK version to `<9.12.0` (e.g., `launchdarkly-server-sdk<9.12.0`).
• gotcha The `ChangeSet` object in the file data source now strictly requires a `Selector` for updates.
  Fix: If you are using the file data source and directly manipulating `ChangeSet` objects, ensure that every change operation includes a valid `Selector` as specified in the updated API documentation.
• gotcha SDK key validation was added, which performs a basic format check on initialization. Providing an invalid SDK key format may lead to immediate client initialization failure.
  Fix: Always use a valid LaunchDarkly SDK key. Validate your SDK key format if you encounter unexpected client initialization issues on versions 9.12.1 or newer. An SDK key usually starts with 'sdk-'
• gotcha It is crucial to call `ld_client.close()` when your application is shutting down to ensure all pending events are flushed and resources are released. Failing to do so can lead to lost analytics events or resource leaks.
  Fix: Integrate `ld_client.close()` into your application's shutdown process, for example, using a `finally` block or a signal handler in web frameworks.

Install

• pip install launchdarkly-server-sdk Install latest version

Imports

• LdClient

  from launchdarkly_server_sdk import LdClient, Config

  The `ldclient` module directly (without `_server_sdk`) is an older pattern. It's best to import `LdClient` and `Config` explicitly from `launchdarkly_server_sdk`.

Quickstart

This quickstart demonstrates how to initialize the LaunchDarkly client, define a user, evaluate a feature flag, and properly shut down the client. It uses an environment variable for the SDK key for security. In production, ensure the client is initialized and shut down gracefully with your application's lifecycle.

import os
from launchdarkly_server_sdk import LdClient, Config

# Replace with your actual SDK key from LaunchDarkly
SDK_KEY = os.environ.get('LAUNCHDARKLY_SDK_KEY', 'YOUR_SDK_KEY_HERE')

if not SDK_KEY or SDK_KEY == 'YOUR_SDK_KEY_HERE':
    print("Warning: LAUNCHDARKLY_SDK_KEY environment variable not set or default used. Client will be in offline mode.")
    # In a real application, you might raise an error or handle this differently.
    config = Config(offline=True)
else:
    config = Config()

# Initialize the LaunchDarkly client
ld_client = LdClient(SDK_KEY, config)

# Wait for the client to be initialized (recommended for server-side apps)
if ld_client.is_initialized():
    print("LaunchDarkly client initialized!")

    # Define a user for flag evaluation
    user = {
        "key": "example-user-key",
        "name": "Example User",
        "custom": {
            "group": "beta_testers"
        }
    }

    # Evaluate a feature flag
    flag_value = ld_client.variation("my-feature-flag", user, False)
    print(f"Feature flag 'my-feature-flag' is: {flag_value} for user {user['key']}")

    # Don't forget to shut down the client when your application exits
    ld_client.close()
    print("LaunchDarkly client closed.")
else:
    print("LaunchDarkly client failed to initialize.")
    # Ensure the client is closed even if initialization fails
    ld_client.close()