lazy-env-configurator 0.2.0

Dynamic Config Class Creation using Environment Variables

LAZY_ENV_CONFIGURATOR

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A utility library for Dynamic Config class generation. Now no more repeated boilerplate code...

Before lazy_env_configurator, config classes used to be created as below.

    class BaseConfig:
        APP = os.environ.get("APP")
        APP_ENV = os.environ.get("APP_ENV")

        # authentication related configuration
        # DB Credentials
        DB_USERNAME = os.environ.get("DB_USERNAME")
        DB_PASSWORD = os.environ.get("DB_PASSWORD")
        DB_HOST = os.environ.get("DB_HOST")
        DB_PORT = os.environ.get("DB_PORT")
        DB_NAME = os.environ.get("DB_NAME")
        DB_DRIVER = os.environ.get("DB_DRIVER")

This use to require a lot of boiler plate and redundant code With lazy_env_configurator this can be reduced to below:

from lazy_env_configurator import BaseEnv, BaseConfig as Config_
class BaseConfig(BaseEnv):
    class Config(Config_):
        envs = ('APP',
        'APP_ENV',
        'DB_USERNAME',
        'DB_PASSWORD',
        'DB_PASSWORD',
        'DB_HOST',
        # defaults
        ('DB_PORT',3306),
        'DB_NAME',
        'DB_DRIVER'
        )

Benefits of using lazy_env_configurator over Normal classes

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• Low memory footprint.
• Lazily evaluates environment variable and only loads them when used.
• Once loaded, env variables are cached.
• Get defaults populated, in case of missing env variables.
• env attributes can be overridden easily.
• classes expose instance attribute preventing need to initialization and making it behave singleton.
• Loads .env files by default so you only need to focus on essentials.
• Self Contained Objects if you do not want to sanatise global env variables. contained attribute.

Components

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• BaseConfig: Main Config class for library. This changes behavior of the container class.

  • envs: List or Tuple of env variable to be populated as attributes in container class. Elements of iterable can be a string or tuple with first element as attribute name and second as default, second element Defaults to None. Eg:

  class Config(Config_):
        envs = ('APP',
        'APP_ENV',
        'DB_USERNAME',
        'DB_PASSWORD',
        'DB_PASSWORD',
        'DB_HOST',
        # defaults
        ('DB_PORT',3306),
        'DB_NAME',
        'DB_DRIVER'
        )
  

  • dot_env_path: Path to .env file. This can be a string or pathlib.Path object. defaults to None. Eg:

  class Config(Config_):
        dot_env_path = Path(__file__).parent/'.env'
  

  • contained: This variable is responsible for behaviour of the container. If this is set to False, all the env variables read from .env file would be populated to os.environ and available globally. If this is set to True, environment variables would only be contained in the container itself. This would help to create configuration containers with different env settings. It contained is set to true and no .env file is present, it raises EnvWarning and fallback to Environment variables. Eg:

  class Config(BaseConfig):
        envs = ("FOO", "APP")
        dot_env_path = Path(__file__).parent / ".env.contained"
        contained = True
  

• BaseEnv: This class will be used as a Base Class for all the containers. It uses EnvMeta as metaclass to populate env variables as attributes on Container Class. Eg:

  from lazy_env_configurator import BaseEnv, BaseConfig as Config_
  class BaseConfig(BaseEnv):
      class Config(Config_):
          envs = ('APP',
          'APP_ENV',
          'DB_USERNAME',
          'DB_PASSWORD',
          'DB_PASSWORD',
          'DB_HOST',
          # defaults
          ('DB_PORT',3306),
          'DB_NAME',
          'DB_DRIVER'
          )
  

  Note: Config class is optional. If not provided, it will not load any env variables. Config class won't be available as an attribute on the child class.

• EnvMeta: Metaclass for populating env variables as class attributes to the child class. if the child class has a Config class, it will be used to populate the env variables.

  by default, the env variables are populated on first access and cached for subsequent access. This can be overriden by setting the value on the instance.

  if the env variable is not set, it uses the default value provided.

  This class also initializes the instance of the child class and make it available as instance attribute on the child class. So it can be accessed as ChildClass.instance.

  Example:
  
  class ABC(BaseEnv):
    def generate_uri(self):
        return f'{self.DB_HOST}:{self.DB_PORT}'
    class Config(BaseConfig):
        envs = ('dev', ('test', 'test_value'),
                'prd', 'DB_HOST', 'DB_PORT')
        dot_env_path = Path(__file__).parent / '.env.test'
  
    >>> # access env variables
    >>> ABC.instance.dev
    >>> ABC.instance.test
    >>> ABC.instance.prd
  

How to use

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Let us refer below example:

from lazy_env_configurator import BaseEnv, BaseConfig as Config_
class BaseConfig(BaseEnv):
    class Config(Config_):
        envs = ('APP',
        'APP_ENV',
        'DB_USERNAME',
        'DB_PASSWORD',
        'DB_PASSWORD',
        'DB_HOST',
        # defaults
        ('DB_PORT',3306),
        'DB_NAME',
        'DB_DRIVER'
        )

We can now use BaseConfig class create as below.

>>> BaseConfig.instance.APP

Every class, subclassed from BaseEnv would expose .instance attribute which will be instance of the subclass. This instance can be used to access all the attributes on the class.

For simplicity, metaclass pre-initialises created class, so to make it behave as singleton.

How this works ?

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lazy_env_configurator uses descriptors under the hood to dynamically populate env variables as attributes, thus making them available on demand, Lazily.