kelvin-app-storage 1.0.0

Library for storing and retrieving state of Kelvin applications.

kelvin-app-storage

Redis-backed storage client for Kelvin applications. Keys are automatically prefixed with the application name and version derived from app.yaml.

Installation

pip install kelvin-app-storage

Prerequisites

A running Redis instance is required. For local development:

docker run -d --name redis -p 6379:6379 redis

Quick Start

from kelvin_app_storage import StorageClient

client = StorageClient()

# Store and retrieve values
client.set("sensor_id", "abc-123")
client.get("sensor_id")  # "abc-123"

# List all stored keys
client.list_keys()  # ["myapp_1.0_sensor_id"]

# Print a formatted table of all stored key-value pairs
print(client)

Disable Key Prefixing

By default, keys are prefixed with <app_name>_<app_version>_ derived from app.yaml. To store keys without a prefix:

client = StorageClient(no_prefix=True)

Supported Value Types

The client automatically serializes and deserializes the following types:

Type	Storage Format
str	Stored as-is
int	String representation
float	String representation
bool	"true" / "false"
list	JSON string
dict	JSON string

client.set("count", 42)
client.get("count")  # 42

client.set("config", {"threshold": 0.8, "enabled": True})
client.get("config")  # {"threshold": 0.8, "enabled": True}

client.set("tags", ["pressure", "temperature"])
client.get("tags")  # ["pressure", "temperature"]

Configuration

The client is configured via environment variables:

Environment Variable	Default	Description
KELVIN_APP_STORAGE_HOST	kelvin-app-storage.app	Redis host
KELVIN_APP_STORAGE_PORT	6379	Redis port
KELVIN_APP_STORAGE_PREFIX	Derived from app.yaml	Custom key prefix (overrides app.yaml)
KELVIN_APP_STORAGE_LOG_LEVEL	INFO	Log level (DEBUG or INFO)

Key Prefix via app.yaml

When no custom prefix is set, the key prefix is derived from app.yaml in the current working directory:

info:
  name: myapp
  version: "1.0"

This produces the prefix myapp_1.0, so a key sensor_id becomes myapp_1.0_sensor_id in Redis.

If app.yaml is missing or unreadable, a random UUID is used as the fallback prefix.

API Reference

StorageClient(no_prefix: bool = False)

Creates a new storage client and connects to Redis.

• no_prefix -- If True, keys are stored without any prefix.
• Raises ValueError if KELVIN_APP_STORAGE_PORT is not a valid integer.
• Raises redis.ConnectionError if Redis is unreachable.

client.get(key: str) -> Any

Retrieves and deserializes the value for the given key. Returns None if the key does not exist.

client.set(key: str, value: Any) -> bool

Serializes and stores a value. Returns True on success. Raises TypeError for unsupported value types.

client.list_keys() -> list

Returns all keys currently stored in Redis.