Harness Feature Flags Python SDK

Warnings

• gotcha Older versions of the SDK (prior to 1.6.4) had issues with rigidly pinned `tenacity` and `typing_extensions` dependencies, potentially causing conflicts with other libraries in your project. Ensure you are using version 1.6.4 or newer for improved dependency management.
  Fix: Upgrade to `harness-featureflags` version 1.6.4 or later using `pip install --upgrade harness-featureflags`.
• gotcha SDK initialization failures are commonly caused by an invalid Server SDK Key or network connectivity issues to the Harness Feature Flags configuration service (https://config.ff.harness.io/api/1.0). Verify your key and network access.
  Fix: Double-check your `API_KEY` against the one provided in the Harness Platform. Ensure your application's environment has outbound network access to the Harness configuration URL. Listen for the `Event.FAILED` event during SDK initialization for more detailed error information.
• gotcha By default, the SDK uses both streaming (for real-time updates) and polling (as a fallback). In case of connection issues, the SDK will gracefully degrade, either serving the most recently cached flag state or the default variation provided in the `variation` call if no cached value exists. Ensure your application logic accounts for these fallback scenarios to prevent unexpected behavior.
  Fix: Design your application with robust fallback logic using the default values in `variation` calls. For advanced control, you can configure streaming/polling behavior and HTTP client options (e.g., via `with_httpx_args` introduced in v1.7.0) to suit your environment's needs, such as disabling streaming for consistent session flags if updates are not required.

Install

• pip install harness-featureflags Install latest version

Imports

• CfClient

  from harness_featureflags.client import CfClient

Quickstart

This quickstart code demonstrates how to initialize the Harness Feature Flags Python SDK, define a target, and evaluate boolean and string feature flags. It continuously checks flag variations and prints their status until interrupted. Remember to replace `FF_API_KEY` with your actual Server SDK Key and update flag identifiers as needed. The SDK handles connection, caching, and updates automatically.

import os
import time
from harness_featureflags.client import CfClient
from harness_featureflags.util import Target

# Set your Harness Server SDK Key as an environment variable or replace directly
API_KEY = os.environ.get('FF_API_KEY', 'YOUR_HAARNESS_SDK_KEY')
# Set a target identifier for your user or application
TARGET_IDENTIFIER = os.environ.get('FF_TARGET_IDENTIFIER', 'test-user-1')

if not API_KEY or API_KEY == 'YOUR_HAARNESS_SDK_KEY':
    print("Error: FF_API_KEY not set. Please set the environment variable or replace the placeholder.")
    exit(1)

def main():
    client = CfClient(API_KEY)
    
    # Wait for the SDK to initialize
    client.wait_for_initialization()

    target = Target(
        identifier=TARGET_IDENTIFIER,
        name=TARGET_IDENTIFIER,
        attributes={
            "email": f"{TARGET_IDENTIFIER}@example.com",
            "country": "US"
        }
    )

    print(f"Client initialized. Target: {target.identifier}")

    try:
        while True:
            # Replace 'harnessappdemodarkmode' with your actual feature flag identifier
            is_dark_mode_enabled = client.bool_variation('harnessappdemodarkmode', target, False)
            print(f"Feature flag 'harnessappdemodarkmode' is {'enabled' if is_dark_mode_enabled else 'disabled'} for target {target.identifier}")

            string_flag_value = client.string_variation('another_string_flag', target, 'default_string')
            print(f"Feature flag 'another_string_flag' has value: {string_flag_value}")

            time.sleep(10)
    except KeyboardInterrupt:
        print("Stopping...")
    finally:
        client.close()
        print("SDK Closed.")

if __name__ == '__main__':
    main()