Eppo Python SDK

Eppo is a modular flagging and experimentation analysis tool. Eppo's Python SDK is built to make assignments in multi-user server side contexts. Before proceeding you'll need an Eppo account.

Features

• Feature gates
• Kill switches
• Progressive rollouts
• A/B/n experiments
• Mutually exclusive experiments (Layers)
• Dynamic configuration

Installation

pip install eppo-server-sdk

Quick start

Begin by initializing a singleton instance of Eppo's client. Once initialized, the client can be used to make assignments anywhere in your app.

Initialize once

import eppo_client
from eppo_client.config import Config, AssignmentLogger

client_config = Config(api_key="<SDK-KEY-FROM-DASHBOARD>")
eppo_client.init(client_config)

Assign anywhere

import eppo_client

client = eppo_client.get_instance()
user = get_current_user()

variation = eppoClient.get_boolean_assignment(
    'show-new-feature', 
    user.id, 
    { 'country': user.country }, 
    False
)

Assignment functions

Every Eppo flag has a return type that is set once on creation in the dashboard. Once a flag is created, assignments in code should be made using the corresponding typed function:

get_boolean_assignment(...)
get_numeric_assignment(...)
get_integer_assignment(...)
get_string_assignment(...)
get_json_assignment(...)

Each function has the same signature, but returns the type in the function name. For booleans use get_boolean_assignment, which has the following signature:

get_boolean_assignment(
    flag_key: str,
    subject_key: str,
    subject_attributes: Dict[str, Any],
    default_value: bool
) -> bool:

Initialization options

The init function accepts the following optional configuration arguments.

Option	Type	Description	Default
assignment_logger	AssignmentLogger	A callback that sends each assignment to your data warehouse. Required only for experiment analysis. See example below.	None
is_graceful_mode	bool	When true, gracefully handles all exceptions within the assignment function and returns the default value.	True

Assignment logger

To use the Eppo SDK for experiments that require analysis, pass in a callback logging function to the init function on SDK initialization. The SDK invokes the callback to capture assignment data whenever a variation is assigned. The assignment data is needed in the warehouse to perform analysis.

The code below illustrates an example implementation of a logging callback using Segment, but you can use any system you'd like. The only requirement is that the SDK receives a log_assignment callback function. Here we define an implementation of the Eppo SegmentAssignmentLogger interface containing a single function named log_assignment:

from eppo_client.assignment_logger import AssignmentLogger
import analytics

# Connect to Segment.
analytics.write_key = "<SEGMENT_WRITE_KEY>"

class SegmentAssignmentLogger(AssignmentLogger):
    def log_assignment(self, assignment):
        analytics.track(assignment["subject"], "Eppo Randomization Assignment", assignment)

client_config = Config(api_key="<SDK-KEY-FROM-DASHBOARD>", assignment_logger=SegmentAssignmentLogger())

Philosophy

Eppo's SDKs are built for simplicity, speed and reliability. Flag configurations are compressed and distributed over a global CDN (Fastly), typically reaching your servers in under 15ms. Server SDKs continue polling Eppo’s API at 30-second intervals. Configurations are then cached locally, ensuring that each assignment is made instantly. Evaluation logic within each SDK consists of a few lines of simple numeric and string comparisons. The typed functions listed above are all developers need to understand, abstracting away the complexity of the Eppo's underlying (and expanding) feature set.