shipeasy (Python)

Server SDK for Shipeasy — feature flags, remote configs, A/B experiments, and metric tracking. Server-key only, never embed in browsers.

pip install shipeasy

Quick start — configure() once, then Client(user) per request

Configure the SDK once at process start with your server key and an optional attributes transform (your user object → the Shipeasy attribute map). Then construct a cheap, user-bound Client(user) per request — every call takes no user argument, because the user is bound at construction.

import shipeasy

# Once, at startup. `attributes` maps YOUR user object to the attribute map
# Shipeasy targets on. Omit it if your user object is already that map.
shipeasy.configure(
    api_key="sdk_server_...",
    attributes=lambda u: {"user_id": u.id, "country": u.country, "plan": u.plan},
)

# Per request — bind the user once, then ask without re-passing it.
client = shipeasy.Client(current_user)

if client.get_flag("new_checkout"):
    ...

config = client.get_config("billing_copy")

result = client.get_experiment("checkout_button", default_params={"color": "blue"})
print(result.in_experiment, result.group, result.params)

configure() builds a single shared Engine (first-config-wins) and kicks off a one-shot fetch fire-and-forget, so the first Client(user).get_flag(...) resolves against real rules. For a long-running server that wants the background poll, pass init=False and call init() on the returned engine:

engine = shipeasy.configure(api_key="sdk_server_...", init=False)
engine.init()  # background poll

If your user object is already the attribute map, omit attributes (the default is identity):

shipeasy.configure(api_key="sdk_server_...")
shipeasy.Client({"user_id": "u_123", "country": "US"}).get_flag("new_checkout")

Constructing Client(user) before configure() raises RuntimeError.

Low-level: the Engine directly

Client(user) is a thin handle over an Engine. You can also use the engine directly — it takes the user on each call and owns track(), see(), the override_* setters, and the offline factories:

from shipeasy import Engine

engine = Engine(api_key="sdk_server_...")
engine.init()  # background poll; use init_once() for serverless

if engine.get_flag("new_checkout", {"user_id": "u_123", "country": "US"}):
    ...

config = engine.get_config("billing_copy")

result = engine.get_experiment(
    "checkout_button",
    user={"user_id": "u_123"},
    default_params={"color": "blue"},
)
print(result.in_experiment, result.group, result.params)

engine.track("u_123", "purchase", {"amount": 49})

Breaking change in 0.8.0: the heavyweight client class was renamed Client → Engine, and Client is now the lightweight user-bound handle above. Replace Client(api_key=...) with Engine(api_key=...) (and Client.for_testing()/from_snapshot/from_file with Engine.*), or adopt configure() + Client(user).

Anonymous visitors (zero-config bucketing)

For logged-out traffic you need a stable unit so a fractional rollout buckets the same on the server and in the browser. The middleware mints a first-party __se_anon_id cookie (shared with every Shipeasy SDK) for any request without one; evaluations then default to it as anonymous_id, so get_flag on an anonymous request just works — no per-call wiring.

# WSGI (Flask, Django, ...)
from shipeasy.middleware import AnonIdMiddleware
app.wsgi_app = AnonIdMiddleware(app.wsgi_app)

# ASGI (FastAPI, Starlette)
from shipeasy.middleware import AnonIdASGIMiddleware
app.add_middleware(AnonIdASGIMiddleware)

# logged-out request → buckets on the __se_anon_id cookie automatically
shipeasy.Client({}).get_flag("new_checkout")
# (or, low-level: engine.get_flag("new_checkout", {}))

An explicit user_id/anonymous_id always wins. The id is also on the request (environ["shipeasy.anon_id"]). The cookie is non-HttpOnly by design so the browser SDK buckets identically; a request with no unit still resolves a fully-rolled (100%) gate as on. Cookie name + format are a cross-SDK contract — see 18-identity-bucketing.md.

Server-side rendering (SSR)

Emit the request's evaluated flags as a declarative <script> tag so the browser SDK has them on first paint. bootstrap_script_tag carries the payload in data-* attributes (no key); the static se-bootstrap.js loader hydrates window.__SE_BOOTSTRAP and writes the __se_anon_id cookie so the browser buckets identically to the server.

user = {"user_id": "u_123"}

# Two tags for the document <head>. The PUBLIC client key (not the server
# key) goes on the i18n loader tag.
head = engine.bootstrap_script_tag(user, anon_id=anon_id) \
     + engine.i18n_script_tag(client_key, "en:prod")

# …or get the raw payload ({"flags", "configs", "experiments", "killswitches"}):
boot = engine.evaluate(user)

bootstrap_script_tag also accepts i18n_profile= and base_url= (defaults to https://cdn.shipeasy.ai).

Default values

get_flag and get_config take a default that is returned only when the value cannot be evaluated — never when it simply resolves off:

# default is returned only if the engine isn't initialized OR the gate isn't
# in the blob. A gate that evaluates to False returns False, not the default.
# Bound:      shipeasy.Client(user).get_flag("new_checkout", default=True)
engine.get_flag("new_checkout", {"user_id": "u_123"}, default=True)

# default is returned when the config key is absent (or decode raises).
engine.get_config("billing_copy", default={"title": "Welcome"})
engine.get_config("limits", decode=lambda v: v["max"], default=0)

Evaluation detail

get_flag_detail returns a FlagDetail(value, reason) so you can log why a flag resolved the way it did. reason is one of the exported constants:

from shipeasy import (
    FlagDetail, CLIENT_NOT_READY, FLAG_NOT_FOUND, OFF, OVERRIDE, RULE_MATCH, DEFAULT,
)

d = engine.get_flag_detail("new_checkout", {"user_id": "u_123"})
# Bound: d = shipeasy.Client(user).get_flag_detail("new_checkout")
print(d.value, d.reason)  # e.g. True RULE_MATCH

get_flag delegates to get_flag_detail and returns .value (substituting default for CLIENT_NOT_READY/FLAG_NOT_FOUND).

Change listeners

Register a callback fired after a background poll fetches new data (a 200, not a 304). It returns an unsubscribe callable. Listeners never fire in test/offline mode.

unsubscribe = engine.on_change(lambda: print("flags changed, rebuild cache"))
...
unsubscribe()  # stop listening

Offline snapshot

Run fully offline from a JSON snapshot — handy for tests, local dev, or air-gapped CI. Evaluations run the real eval logic against the snapshot; no network is ever touched (init()/init_once()/track() are no-ops) and override_* setters still apply on top.

# From a file: { "flags": <body of /sdk/flags>, "experiments": <body of /sdk/experiments> }
engine = Engine.from_file("shipeasy-snapshot.json")

# Or from in-memory blobs
engine = Engine.from_snapshot(
    flags={"gates": {...}, "configs": {...}},
    experiments={"experiments": {...}, "universes": {...}},
)

engine.get_flag("new_checkout", {"user_id": "u_123"})

Testing

Use Engine.for_testing() for unit tests: it does zero network, needs no api_key, disables telemetry, and makes init()/init_once()/track() no-ops. Seed every entity with the override_* setters (Statsig-style local overrides) — an override always wins over whatever the engine would otherwise resolve.

from shipeasy import Engine

engine = Engine.for_testing()  # no key, no network, immediately usable

# Flags
engine.override_flag("new_checkout", True)
assert engine.get_flag("new_checkout", {"user_id": "u_123"}) is True

# Configs (decode is optional and still applies)
engine.override_config("billing_copy", {"title": "Welcome"})
assert engine.get_config("billing_copy") == {"title": "Welcome"}
assert engine.get_config("billing_copy", decode=lambda v: v["title"]) == "Welcome"

# Experiments → ExperimentResult(in_experiment=True, group=..., params=...)
engine.override_experiment("checkout_button", group="treatment", params={"color": "green"})
result = engine.get_experiment(
    "checkout_button",
    user={"user_id": "u_123"},
    default_params={"color": "blue"},
)
assert result.in_experiment and result.group == "treatment"
assert result.params == {"color": "green"}

# track() is a no-op in test mode — safe to call, sends nothing
engine.track("u_123", "purchase", {"amount": 49})

# Reset between cases
engine.clear_overrides()

The same override_* / clear_overrides() setters also work on a normal Engine if you want to pin a value in a live engine.

Evaluation

Tested against the cross-language MurmurHash3 vectors in experiment-platform/04-evaluation.md.