typed-settings 0.6

Typed settings based on attrs classes

Typed Settings

This package allows you to cleanly structure your settings with attrs classes. Type annotations will be used to automatically convert values to the proper type[^1]. You can currently load settings from these sources:

• TOML files (multiple, if you want to). Paths can statically specified or dynamically set via a environment variable.
• Environment variables
• click command line options

You can use Typed settings, e.g., for

• server processes
• containerized apps
• command line applications

[^1]: Not yet: https://github.com/python-attrs/attrs/pull/653

Examples

Hello, World!, with env. vars.

This is a very simple example that demonstrates how you can load settings from environment variables.

# example.py
import typed_settings as ts

@ts.settings
class Settings:
    option: str

settings = ts.load_settings(cls=Settings, appname="example")
print(settings)

$ EXAMPLE_OPTION="Hello, World!" python example.py
Settings(option='Hello, World!')

Nested classes and config files

Settings classes can be nested. Config files define a different section for each class.

# example.py
import click

import typed_settings as ts

@ts.settings
class Host:
    name: str
    port: int = ts.option(converter=int)

@ts.settings(kw_only=True)
class Settings:
    host: Host = ts.option(converter=lambda d: Host(**d))
    endpoint: str
    retries: int = 3

settings = ts.load_settings(
    cls=Settings, appname='example', config_files=['settings.toml']
)
print(settings)

# settings.toml
[example]
endpoint = "/spam"

[example.host]
name = "example.com"
port = 443

$ python example.py
Settings(host=Host(name='example.com', port=443), endpoint='/spam', retries=3)

Click

Optionally, click options can be generated for each option. Config files and environment variables will still be read and can be overriden by passing command line options.

# example.py
import click
import typed_settings as ts

@ts.settings
class Settings:
    a_str: str = "default"
    an_int: int = 3

@click.command()
@ts.click_options(Settings, 'example')
def main(settings):
    print(settings)

if __name__ == '__main__':
    main()

$ python example.py --help
Usage: example.py [OPTIONS]

Options:
  --a-str TEXT      [default: default]
  --an-int INTEGER  [default: 3]
  --help            Show this message and exit.
$ python example.py --a-str=spam --an-int=1
Settings(a_str='spam', an_int=1)

Features

• Settings are defined as type-hinted attrs classes.

• Typed Settings’ settings decorator adds automatic type converstion for option values and makes your settings class frozen (immutable) by default.

• Settings can currently be loaded from:

  • TOML files
  • Environment variables
  • click Commaoptions

• Paths to settings files can be “hard-coded” into your code or specified via an environment variable.

• Order of precedence:

  • Default value from settings class
  • First file from hard-coded config files list
  • ...
  • Last file from hard-coded config files list
  • First file from config files env var
  • ...
  • Last file from config files env var
  • Environment variable {PREFIX}_{SETTING_NAME}
  • (Value passed to Click option)

• Config files are “optional” by default – no error is raised if a specified file does not exist.

• Config files can be marked as mandatory by prefixing them with an !.