featbit-sdks-python

What this skill does

# FeatBit Python Server SDK

## When to Use This Skill

Use for server-side Python applications — Flask, Django, FastAPI, background workers, or scripts — that evaluate feature flags on the backend.

**Why server SDK**: Flags sync via WebSocket on startup (<100ms) and are evaluated locally with no remote call per request. The process holds one persistent singleton client.

Do not use for browser JavaScript, React, React Native, or any frontend context.

## Source

https://github.com/featbit/featbit-python-sdk

## Setup Workflow

Copy and track progress:
- [ ] Step 1: Install the package
- [ ] Step 2: Configure the singleton client
- [ ] Step 3: Evaluate the first feature flag
- [ ] Step 4: Shut down cleanly

**Step 1: Install the package**

Run:

```bash
pip install fb-python-sdk
```

**Step 2: Configure the singleton client**

```python
from fbclient import get, set_config
from fbclient.config import Config

set_config(Config(
    env_secret='<your-env-secret>',
    event_url='http://localhost:5100',
    streaming_url='ws://localhost:5100'
))
client = get()
```

**Why `set_config` + `get()`**: This initializes a process-wide singleton. Call `set_config` once at application startup; every subsequent `get()` returns the same instance.

**Step 3: Evaluate the first feature flag**

```python
if client.initialize:
    user = {'key': 'user-key-123', 'name': 'Jane'}
    detail = client.variation_detail('flag-key', user, default=None)
    print(f'flag returns {detail.variation}, reason: {detail.reason}')
```

**Why check `client.initialize`**: This property (no parentheses) confirms the SDK has synced flag data. If false, `env_secret`, `event_url`, or `streaming_url` is likely wrong.

**Step 4: Shut down cleanly**

```python
client.stop()
```

Call `client.stop()` when the process exits to flush pending analytics events.

## Feature Flag Evaluation

```python
user = {'key': 'user-key-123', 'name': 'Jane'}

# Value only
flag_value = client.variation('flag-key', user, False)

# Value + reason
detail = client.variation_detail('flag-key', user, default=None)
print(detail.variation)  # the resolved value
print(detail.reason)     # why this value was returned

# All flags for a user
all_flags = client.get_all_latest_flag_variations(user)
```

Use `variation` when only the resolved value is needed. Use `variation_detail` when the caller needs to know why a specific value was returned (targeting rule, default, etc.).

## User Custom Properties

The Python SDK represents a user as a plain `dict`. Add any extra keys directly — no builder class is required:

```python
user = {
    'key': 'bob-id',       # required: unique identifier
    'name': 'Bob',         # required: display name
    'age': 25,             # custom property
    'country': 'FR',       # custom property
    'plan': 'premium',     # custom property
}
flag_value = client.variation('flag-key', user, False)
```

FeatBit targeting rules can reference any key in this dict.

## Read Next Only When Needed

- [Flag tracking / listeners](https://github.com/featbit/featbit-python-sdk#flag-tracking) — only when the user asks about reacting to flag changes at runtime.
- [Experiments / A-B testing](https://github.com/featbit/featbit-python-sdk#experiments-abn-testing) — only when the user asks about `track_metric` or experiment events.
- [Offline mode](https://github.com/featbit/featbit-python-sdk#offline-mode) — only when the user asks about `Config(..., offline=True)` or bootstrapping without a server.
- [Data synchronization](https://github.com/featbit/featbit-python-sdk#data-synchonization) — only when the user asks about WebSocket reconnect or sync behavior.
- [FBClient reference](https://github.com/featbit/featbit-python-sdk#fbclient) — only when the user asks about advanced client configuration or lifecycle options.