Python

Flags in Python, on the server.

pip install variably-sdk

The client takes one argument

A config dict, or a VariablyConfig. Not keyword arguments — VariablyClient(api_key=...) raises TypeError.

import os
from variably import VariablyClient

client = VariablyClient({
    "api_key": os.environ["VARIABLY_API_KEY"],
    "base_url": os.environ["VARIABLY_BASE_URL"],
})

base_url is required and has no default, so evaluation data cannot be sent to an unintended host. timeout (milliseconds, default 5000), retry_attempts, cache and log_level are also accepted.

Reading flags

The context is user_id, not key — that spelling differs from the JavaScript SDKs.

user = {"user_id": "user-123", "country": "JP"}

enabled = client.evaluate_flag_bool("checkoutRedesign", False, user)
layout  = client.evaluate_flag_string("checkoutLayout", "control", user)
count   = client.evaluate_flag_number("maxItems", 10, user)
config  = client.evaluate_flag_json("checkoutConfig", {}, user)

flags = client.all_flags(user)

Note the argument order: flag key, default, context.

Catch missing flags at start-up

missing = client.validate_flags(["checkoutRedesign", "newPricing"], user)
if missing:
    raise RuntimeError(f"Flags not defined in Variably: {', '.join(missing)}")

A flag the project does not define is an error rather than a value. A typo or an unseeded environment would otherwise look exactly like a flag that is switched off, and the application would run on defaults appearing healthy.

The same package does LLM evaluation

variably-sdk also carries observe() for scoring LLM output. If you arrived here from Setup you already have it installed — the flag client above is the same package.