The final loader
The Stela Final Loader¶
Stela always loads the data from the dotenv files, we call it the First Loader.
After that, Stela calls the Final Loader function, which just return the data received from the First Loader.
You can configure Stela to use your own Final Loader function, or use the default one.
Stela Final Loader is a function that receives two arguments:
- The Stela Options object:
options - The dictionary content the data from dotenvs read based on current stela options:
env_data
And it's the last code called for before returning the env object.
Default Stela Final Loader code¶
Default behavior is just return data parsed from Env files:
from stela.config import StelaOptions
def default_loader(
options: StelaOptions,
env_data: dict[str, any]
) -> dict[str, any]:
"""Stela Default Loader.
Default Action is just return the env_data received.
:param options: Stela Options
:param env_data: Dict with environment data
:return: Dict
"""
from loguru import logger
logger.info(
f"Using Stela Default Loader. "
f"Current environment is: {options.current_environment}"
)
return env_data
The Stela Options object¶
All stela options are attributes in this object. Please check Settings for the complete list.
Creating your custom Final Loader¶
If you need to get your Environment variables from other sources than dotenv files, or need to mix data, you can use your own logic for the Loader. Just inform Stela which function needs to be called:
This function will be called, and need to receive the two parameters above: options and env_data and it must return
a valid python dictionary.
Examples¶
Read data from toml file¶
import toml
from typing import Any
from stela.config import StelaOptions
from stela.utils import merge_env
def pyproject_loader(options: StelaOptions, env_data: dict[str, Any]) -> dict[str, Any]:
"""Load settings from pyproject.toml to current Stela data.
Data returned must be a Python Dictionary.
:param env_data: Data parsed from dotenv files
:param options: Stela Options obj
:return Dict[str, Any]
"""
filepath = "pyproject.toml"
sub_table = "environment" # The sub table inside toml which holds your settings
# Read toml data for the sub table
toml_data = toml.load(filepath)
sub_table_data = toml_data.get(sub_table, {})
# Update toml data with dotenv info
# The sub_table_data are the "default" settings.
# The env_data are the final ones.
project_settings = merge_env(sub_table_data, env_data)
return project_settings
Read data from AWS System Manager Parameter Store¶
import boto3
from typing import Any
from stela.config import StelaOptions
def ssm_loader(options: StelaOptions, env_data: dict[str, Any]) -> dict[str, Any]:
"""Load settings from AWS Parameter Store (SSM) to current Stela data.
Data returned must be a Python Dictionary.
:param env_data: Data parsed from dotenv file
:param options: Stela Options obj
:return Dict[str, Any]
"""
ssm = boto3.client('ssm')
environment = options.current_environment
# Get from SSM
response = ssm.get_parameters_by_path(
Path=f'/my-project/{environment}',
WithDecryption=True
)
ssm_data = {parameter["Name"].upper(): parameter["Value"] for parameter in response["Parameters"]}
# Overwrite env_data with SSM data
# Normally information on remote sources
# like vaults, are the final ones
env_data.update(ssm_data)
return env_data
The goal here is: One Interface, Any Sources
You can use any source or logic to load your environment variables. They can have the complexity you need for the project you're working. But the interface to work with these values is always the same.
Different Loaders per Environment¶
If you need different custom loaders per environment, you can use Stela Environment variables to do this:
For the next step, let's review how to integrate Stela with many popular Python packages and Frameworks.