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Typed settings based on attrs classes

Project description

Typed Settings

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Typed Settings allows you to cleanly structure your settings with attrs classes. Type annotations will be used to automatically convert values to the proper type (using cattrs). You can currently load settings from these sources:

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

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

  • server processes
  • containerized apps
  • command line applications
  • scripts and tools for scientific experiments and data analysis

The documentation contains a full list of all features.

Installation

Install and update using pip:

$ python -m pip install typed-settings

You can install dependencies for optional features via

$ python -m pip install typed-settings[<feature>]

Available features:

  • typed-settings[click]: Enable support for Click options
  • typed-settings[option-groups]: Enable support for Click and Click option groups
  • typed-settings[all]: Install all optional requirements

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(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.settings(kw_only=True)
class Settings:
    host: Host
    endpoint: str
    retries: int = 3

settings = ts.load(
    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)

Configurable settings loaders

The first example used a convenience shortcut with pre-configured settings loaders. However, Typed Settings lets you explicitly configure which loaders are used and how they work:

# example.py
import typed_settings as ts

@ts.settings
class Settings:
    option: str

settings = ts.load_settings(
    cls=Settings,
    loaders=[
        ts.FileLoader(
            files=[],
            env_var="EXAMPLE_SETTINGS",
            formats={
                "*.toml": ts.TomlFormat("example"),
            },
        ),
        ts.EnvLoader(prefix="EXAMPLE_"),
      ],
)
print(settings)
$ EXAMPLE_OPTION="Hello, World!" python example.py
Settings(option='Hello, World!')

In order to write your own loaders or support new file formats, you need to implement the Loader or FileFormat protocols.

You can also pass a custom cattrs converter to add support for additional Python types.

Command Line Interfaces

Typed Settings can generate a command line interfaces (CLI) based on your settings. These CLIs will load settings as described above and let users override the loades settings with command line argumments.

Typed Settings supports argparse and click.

Argparse

# example.py
import typed_settings as ts

@ts.settings
class Settings:
    a_str: str = ts.option(default="default", help="A string")
    an_int: int = ts.option(default=3, help="An int")

@ts.cli(Settings, "example")
def main(settings):
    print(settings)

if __name__ == "__main__":
    main()
$ python example.py --help
usage: example.py [-h] [--a-str TEXT] [--an-int INT]

options:
  -h, --help    show this help message and exit

Settings:
  Settings options

  --a-str TEXT  A string [default: default]
  --an-int INT  An int [default: 3]
$ python example.py --a-str=spam --an-int=1
Settings(a_str='spam', an_int=1)

Click

# example.py
import click
import typed_settings as ts

@ts.settings
class Settings:
    a_str: str = ts.option(default="default", help="A string")
    an_int: int = ts.option(default=3, help="An int")

@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      A string  [default: default]
  --an-int INTEGER  An int  [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 is an alias to attrs.define and can optionally make your settings frozen (immutable).

  • option() and secret() are wrappers around attrs.field() and add meta data handling for Click options.

  • secret() attributes have string representation that masks the actual value, so that you can safely print or log settings instances.

  • Settings can currently be loaded from:

    • TOML files
    • Python files
    • Environment variables
    • Click command line options
  • Settings are converted to their correct type using cattrs.

    • Users can extend the default converter with hooks for custom types
    • Lists can be loaded from strings from environment variables. String-to-list conversion can be configured. Strings can be JSON structues or simple comma (or colon) speparated lists (e.g., "1,2,3" or "path1:path2").
  • Paths to settings files can be

    • “hard-coded” into your code,
    • dynamically searched from the CWD upwards via find(filename), 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 !.

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