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Python SDK Reference

This topic describes how to use the Harness Feature Flags Java SDK for your Java application.

For getting started quickly, you can use our sample code from the Python SDK README. You can also clone and run a sample application from the Python SDK GitHub Repository.

Before You Begin

You should read and understand the following:


The current version of this SDK is 1.1.9.


To use this SDK, make sure you:  

Install the SDK

Install the python SDK using pip

python -m pip install harness-featureflags

Initialize the SDK

To initialize the Python SDK, you need to:

  1. Add your Server SDK Key to connect to your Harness Environment.
  2. Add a Target that you want to Evaluate against a Feature Flag.
  3. (Optional) Configure the SDK options. For more details on what features you can configure for this SDK, go to Configure the SDK.

Add the Server SDK Key

To connect to the correct Environment that you set up on the Harness Platform, you need to add the Server SDK Key from that Environment. Input the Server SDK Key into the api_key parameter. For example:

Put the API Key here from your environment
api_key = "YOUR_API_KEY";

cf = CfClient(api_key);

Add a Target

What is a Target?
Targets are used to control which users see which Variation of a Feature Flag, for example, if you want to do internal testing, you can enable the Flag for some users and not others. When creating a Target, you give it a name and a unique identifier. Often Targets are users but you can create a Target from anything that can be uniquely identified, such as an app or a machine.

For more information about Targets, go to Targeting Users With Flags.

To add a Target, build it and pass in arguments for the following:

identifierUnique ID for the Target.Read Regex requirements for Target names and identifiers below for accepted characters.Requiredidentifier='HT_1'
nameName for this Target. This does not have to be unique. Note: If you don’t provide a value, the name will be the same as the identifier.Read Regex requirements for Target names and identifiers below for accepted characters.OptionalNote: If you don't want to send a name, don't send the parameter. Sending an empty argument will cause an"Harness_Target_1"
attributesAdditional data you can store for a Target, such as email addresses or location.Optionalattributes={"email": "[email protected]"}
Regex requirements for Target names and identifiers


Regex: ^[[email protected]_-]*$
Must consist of only alphabetical characters, numbers, and the following symbols:
. (period)
@ (at sign)
_ (underscore)

The characters can be lowercase or uppercase but cannot include accented letters, for example Cafe_789.

Name Regex: ^[\\p{L}\\d [email protected]_-]*$

Must consist of only alphabetical characters, numbers, and the following symbols:
. (period)
@ (at sign)
_ (underscore)

The characters can be lowercase or uppercase and can include accented letters, for example Café_123.

For example:

 target = Target(identifier='HT_1', name="Harness_Target_1", attributes={"email": "[email protected]"})

Configure the SDK

You can configure the following features of the SDK:

NameExampleDescriptionDefault Value
baseUrlwith_base_url("")The URL used to fetch Feature Flag Evaluations. When using the Relay Proxy, change this to: http://localhost:7000
eventUrlwith_events_url("")The URL for posting metrics data to the Feature Flag service. When using the Relay Proxy, change this to: http://localhost:7000
pollIntervalConfig(pull_interval=60)The interval in seconds that we poll for changes when you are using stream mode.60 (seconds)
streamEnabledwith_stream_enabled(True)Set to True to enable streaming mode.Set to False to disable streaming mode.True
analyticsEnabledwith_analytics_enabled(True)Set to True to enable analytics.Set to False to disable analytics.Note: When enabled, analytics data is posted every 60 seconds.True

For example:

# Create a Feature Flag Client  
client = CfClient(apiKey,

Evaluate a Flag

Evaluating a Flag is when the SDK processes all Flag rules and returns the correct Variation of that Flag for the Target you provide. 

If a matching Flag can’t be found, or the SDK can’t remotely fetch flags, the default value is returned. 

There are different methods for the different Variation types and for each method you need to pass in:

  • Identifier of the Flag you want to evaluate
  • The Target object you want to evaluate against
  • The default Variation

For example:

Evaluate a boolean Variation

result = cf.bool_variation("identifier_of_your_bool_flag", target, False);  

Evaluate a string Variation

result = client.string_variation('identifier_of_your_string_flag', target, "")

Evaluate a number Variation

result = client.number_variation('identifier_of_your_number_flag', target, -1)

Evaluate a JSON Variation

client.json_variation('identifier_of_your_json_flag', target, {})

Test your app is connected to Harness

When you receive a response showing the current status of your Feature Flag, go to the Harness Platform and toggle the Flag on and off. Then, check your app to verify if the Flag Variation displayed is updated with the Variation you toggled.

Close the SDK

To help prevent memory leaks, we recommend closing the SDK when it’s not in use. To do this, run the following command: 


Additional options

Configure your logger

The SDK provides a logger that wraps the standard Python logging package. You can import and use it with the following:

from featureflags.util import log"Hello, World!")

To change the default log level, you can use the standard logging levels

from featureflags.util import log  
import logging


Use the Relay Proxy

When using your Feature Flag SDKs with a Harness Relay Proxy you need to change the default URL and events URL to http://localhost:7000 when initializing the SDK. To do this:

  1. Import the URL helper functions, for example:
from featureflags.config import with_base_url  
from featureflags.config import with_events_url
  1. Pass the new URLs in when initializing the SDK, for example:
    client = CfClient(api_key,  

Sample code for a Python application

Here is a sample code for integrating with the Python SDK:

import time  

from featureflags.evaluations.auth_target import Target
from featureflags.client import CfClient
from featureflags.util import log
from featureflags.config import with_base_url
from featureflags.config import with_events_url

def main():
log.debug("Starting example")
api_key = "Your API key"
client = CfClient(api_key,

target = Target(identifier='harness')

while True:
result = client.bool_variation('your_flag_identifier', target, False)
log.debug("Result %s", result)

if __name__ == "__main__":