coveo-settings 3.0

Settings driven by environment variables.

coveo-settings

Whenever you want the user to be able to configure something through an environment variable, this module has your back:

from coveo_settings import StringSetting, BoolSetting

DATABASE_URL = StringSetting('project.database.url')
DATABASE_USE_SSL = BoolSetting('project.database.ssl')

The user can then configure the environment variables project.database.url and project.database.ssl to configure the application.

When accessed, the values are automatically converted to the desired type:

• StringSetting will always be a string
• BoolSetting is either True or False, but accepts "yes|no|true|false|1|0" as input (case-insensitive, of course)
• IntSetting and FloatSetting are self-explanatory
• DictSetting allows you to use JSON maps
• PathSetting gives a Path instance, and also implements PathLike and the / operator

If the input cannot be converted to the value type, an TypeConversionConfigurationError exception is raised.

A default (fallback) value may be specified. The fallback may be a callable.

A validation callback may be specified for custom logic and error messages.

Not limited to environment variables; supports redirection to custom implementations.

A setting can be set as sensitive for logging purposes. When logging, use repr(setting) to get the correct representation.

Accessing the value

There are various ways to obtain the value:

from coveo_settings import BoolSetting

DATABASE_USE_SSL = BoolSetting('project.database.ssl')

# this method will raise an exception if the setting has no value and no fallback
use_ssl = bool(DATABASE_USE_SSL)
use_ssl = DATABASE_USE_SSL.get_or_raise()
assert use_ssl in [True, False]

# this method will not raise an exception
use_ssl = DATABASE_USE_SSL.value
assert use_ssl in [True, False, None]

# use "is_set" to check if there is a value set for this setting; skips validation check
if DATABASE_USE_SSL.is_set:
    use_ssl = bool(DATABASE_USE_SSL)

# use "is_valid" to verify if the value passes the validation callback. implies is_set.
if not DATABASE_USE_SSL.is_valid:
    ...

Loose environment key matching

Matching the key of the environment variable project.database.ssl is done very loosely:

• case-insensitive
• dots and underscores are ignored completely (foo_bar and f__ooba.r are equal)
  • useful for some runners that don't support dots in environment variable keys

Use ready validation

You can quickly validate that a string is in a specific list like this:

from coveo_settings.settings import StringSetting
from coveo_settings.validation import InSequence

ENV = StringSetting("environment", fallback="dev", validation=InSequence("prod", "staging", "dev"))

Redirection

You can register custom redirection schemes in order to support any data source.

Much like https:// is a clear scheme, you may register callback functions to trigger when the value of a setting starts with the scheme(s) you define. For instance, let's support a custom API and a file storage:

from coveo_settings import settings_adapter, StringSetting, ConfigValue


@settings_adapter("internal-api::")
def internal_api_adapter(key: str) -> ConfigValue:
    # the scheme was automatically removed for convenience; only the resource remains
    assert "internal-api::" not in key
    return "internal api"  # implement logic to obtain value from internal api


@settings_adapter("file::", strip_scheme=False)
def file_adapter(key: str) -> ConfigValue:
    # you can keep the scheme by specifying `strip_scheme=False`
    assert key.startswith("file::")
    return "file adapter"  # implement logic to parse the key and retrieve the setting value


assert StringSetting('...', fallback="internal-api::settings/user-name").value == "internal api"
assert StringSetting('...', fallback="file::settings.yaml/user-name").value == "file adapter"


# even though we used `fallback` above, the redirection is driven by the user:
import os

REDIRECT_ME = StringSetting('test')
os.environ['test'] = "file::user.json::name"
assert REDIRECT_ME.value == "file adapter"
os.environ['test'] = "internal-api::url"
assert REDIRECT_ME.value == "internal api"

Keep in mind that there's no restriction on the prefix scheme; it's your responsibility to pick something unique that can be set as the value of an environment variable.

Redirection is recursive

The value of a redirection may be another redirection and may juggle between adapters. A limit of 50 redirections is supported:

import os

from coveo_settings import StringSetting


os.environ["expected"] = "final value"
os.environ["redirected"] = "env->expected"
os.environ["my-setting"] = "env->redirected"

assert StringSetting("my-setting").value == "final value"

Builtin environment redirection

The builtin redirection scheme env-> can be used to redirect to a different environment variable. The example below demonstrates the deprecation/migration of my-setting into new-setting:

import os

from coveo_settings import StringSetting

os.environ["new-setting"] = "correct-value"
os.environ["my-setting"] = "env->new-setting"

assert StringSetting("my-setting").value == "correct-value"

Cached

You can set a setting to cache the first valid value with cached=True. This is particularly useful in redirection scenarios to avoid repeating requests too often.

Setting the value

You can override the value using setting.value = "some value" and clear the override with setting.value = None. Clearing the override resumes the normal behavior of the environment variables and the fallback value, if set.

This is typically used as a way to propagate CLI switches globally. For mocking scenarios, refer to the Mocking section below.

Mocking

When you need a setting value for a test, use the mock_config_value context manager:

from coveo_settings import StringSetting
from coveo_settings.mock import mock_config_value

SETTING = StringSetting(...)

assert not SETTING.is_set
with mock_config_value(SETTING, 'new-value'):
    assert SETTING.is_set

You can also clear the value:

from coveo_settings import StringSetting
from coveo_settings.mock import mock_config_value

SETTING = StringSetting(..., fallback='test')

assert SETTING.is_set
with mock_config_value(SETTING, None):
    assert not SETTING.is_set