Replane Python SDK

Python SDK for Replane - a dynamic configuration platform with real-time updates.

Features

• Real-time updates via Server-Sent Events (SSE)
• Context-based overrides for feature flags, A/B testing, and gradual rollouts
• Zero dependencies for sync client (stdlib only)
• Both sync and async clients available
• Type-safe with full type hints
• Testing utilities with in-memory client

Installation

# Basic installation (sync client only, zero dependencies)
pip install replane

# With async support (adds httpx dependency)
pip install replane[async]

Quick Start

Synchronous Client

from replane import SyncReplaneClient

# Using context manager (recommended)
with SyncReplaneClient(
    base_url="https://replane.example.com",
    sdk_key="sk_live_...",
) as client:
    # Get a simple config value
    rate_limit = client.get("rate-limit")

    # Get with context for override evaluation
    feature_enabled = client.get(
        "new-feature",
        context={"user_id": user.id, "plan": user.plan},
    )

    # Get with fallback default
    timeout = client.get("request-timeout", default=30)

Asynchronous Client

Requires pip install replane[async]:

from replane import AsyncReplaneClient

async with AsyncReplaneClient(
    base_url="https://replane.example.com",
    sdk_key="sk_live_...",
) as client:
    # get() is sync since it reads from local cache
    rate_limit = client.get("rate-limit")

    # With context
    enabled = client.get("feature", context={"plan": "premium"})

Configuration Options

Both clients accept the same configuration:

client = SyncReplaneClient(
    base_url="https://replane.example.com",
    sdk_key="sk_live_...",

    # Default context applied to all get() calls
    context={"environment": "production"},

    # Fallback values used if server is unavailable during init
    fallbacks={
        "rate-limit": 100,
        "feature-enabled": False,
    },

    # Configs that must exist (raises error if missing)
    required=["rate-limit", "feature-enabled"],

    # Timeouts in milliseconds
    request_timeout_ms=2000,
    initialization_timeout_ms=5000,
    retry_delay_ms=200,
    inactivity_timeout_ms=30000,
)

Context-Based Overrides

Replane evaluates override rules client-side using the context you provide. Your context data never leaves your application.

# Define context based on current user/request
context = {
    "user_id": "user-123",
    "plan": "premium",
    "region": "us-east",
    "is_beta_tester": True,
}

# Overrides are evaluated locally
value = client.get("feature-flag", context=context)

Override Examples

Percentage rollout (gradual feature release):

# Server config has 10% rollout based on user_id
# Same user always gets same result (deterministic hashing)
enabled = client.get("new-checkout", context={"user_id": user.id})

Plan-based features:

max_items = client.get("max-items", context={"plan": user.plan})
# Returns different values for free/pro/enterprise plans

Geographic targeting:

content = client.get("homepage-banner", context={"country": request.country})

Subscribing to Changes

React to config changes in real-time:

# Subscribe to all config changes
def on_any_change(name: str, config):
    print(f"Config {name} changed to {config.value}")

unsubscribe = client.subscribe(on_any_change)

# Subscribe to specific config
def on_feature_change(config):
    update_feature_state(config.value)

unsubscribe_feature = client.subscribe_config("my-feature", on_feature_change)

# Later: stop receiving updates
unsubscribe()
unsubscribe_feature()

For async clients, callbacks can be async:

async def on_change(name: str, config):
    await notify_services(name, config.value)

client.subscribe(on_change)

Error Handling

from replane import (
    ReplaneError,
    ConfigNotFoundError,
    TimeoutError,
    AuthenticationError,
    NetworkError,
    ErrorCode,
)

try:
    value = client.get("my-config")
except ConfigNotFoundError as e:
    print(f"Config not found: {e.config_name}")
except TimeoutError as e:
    print(f"Timed out after {e.timeout_ms}ms")
except AuthenticationError:
    print("Invalid SDK key")
except ReplaneError as e:
    print(f"Error [{e.code}]: {e.message}")

Testing

Use the in-memory client for unit tests:

from replane.testing import create_test_client, InMemoryReplaneClient

# Simple usage
client = create_test_client({
    "feature-enabled": True,
    "rate-limit": 100,
})

assert client.get("feature-enabled") is True

# With overrides
client = InMemoryReplaneClient()
client.set_config(
    "feature",
    value=False,
    overrides=[{
        "name": "premium-users",
        "conditions": [
            {"operator": "in", "property": "plan", "expected": ["pro", "enterprise"]}
        ],
        "value": True,
    }],
)

assert client.get("feature", context={"plan": "free"}) is False
assert client.get("feature", context={"plan": "pro"}) is True

Pytest Fixture Example

import pytest
from replane.testing import create_test_client

@pytest.fixture
def replane_client():
    return create_test_client({
        "feature-flags": {"dark-mode": True, "new-ui": False},
        "rate-limits": {"default": 100, "premium": 1000},
    })

def test_feature_flag(replane_client):
    flags = replane_client.get("feature-flags")
    assert flags["dark-mode"] is True

Manual Lifecycle Management

If you prefer not to use context managers:

# Sync
client = SyncReplaneClient(base_url="...", sdk_key="...")
client.connect()  # Blocks until initialized
try:
    value = client.get("config")
finally:
    client.close()

# Async
client = AsyncReplaneClient(base_url="...", sdk_key="...")
await client.connect()
try:
    value = client.get("config")
finally:
    await client.close()

Framework Integration

FastAPI

from contextlib import asynccontextmanager
from fastapi import FastAPI, Depends
from replane import AsyncReplaneClient

client: AsyncReplaneClient | None = None

@asynccontextmanager
async def lifespan(app: FastAPI):
    global client
    client = AsyncReplaneClient(
        base_url="https://replane.example.com",
        sdk_key="sk_live_...",
    )
    await client.connect()
    yield
    await client.close()

app = FastAPI(lifespan=lifespan)

def get_replane() -> AsyncReplaneClient:
    assert client is not None
    return client

@app.get("/items")
async def get_items(replane: AsyncReplaneClient = Depends(get_replane)):
    max_items = replane.get("max-items", context={"plan": "free"})
    return {"max_items": max_items}

Flask

from flask import Flask, g
from replane import SyncReplaneClient

app = Flask(__name__)
replane_client: SyncReplaneClient | None = None

@app.before_first_request
def init_replane():
    global replane_client
    replane_client = SyncReplaneClient(
        base_url="https://replane.example.com",
        sdk_key="sk_live_...",
    )
    replane_client.connect()

@app.route("/items")
def get_items():
    max_items = replane_client.get("max-items")
    return {"max_items": max_items}

Requirements

• Python 3.10+
• No dependencies for sync client
• httpx for async client (pip install replane[async])

License

MIT