container-app-conf is a library to easily read application configuration values from multiple sources (YAML, env) while providing type validation.

The initial purpose of this library was to have an easy way to configure an application running inside of a container using environment variables (Docker in this case) and still provide the possibility to use a more simple form of configuration like a YAML file.

container-app-conf is used by

• python-n26
• InfiniteWisdom
• DeineMudda
• py-image-dedup

and hopefully many others :)

pip install container-app-conf

Create a custom configuration class and define your config entries:

from container_app_conf import ConfigBase
from container_app_conf.entry.string import StringConfigEntry

class AppConfig(ConfigBase):

    MY_CONFIG = StringConfigEntry(
        description="This is just a demo text config entry",
        example="example",
        key_path=[
            "my_app",
            "example"
        ],
        required=True)

config = AppConfig()

value = config.MY_CONFIG.value

Oftentimes it can be useful to print the current configuration of an application. To do this you can use

config = AppConfig()
config.print()

which will result in an output similar to this:

test->bool: _REDACTED_
test->this->date->is->nested->deep: 2019-10-22T04:21:02.316907
test->this->is->a->range: [0..100]
test->this->is->a->list: None
test->this->timediff->is->in->this->branch: 0:00:10
test->directory: None
test->file: None
test->float: 1.23
test->int: 100
test->regex: ^[a-zA-Z0-9]$
test->string: default value
secret->list: _REDACTED_
secret->regex: _REDACTED_

If you don't like the style you can specify a custom ConfigFormatter like this:

from container_app_conf.formatter.toml import TomlFormatter
config = AppConfig()
config.print(TomlFormatter())

Which would output the same config like this:

[test]
bool = "_REDACTED_"
float = 1.23
int = 100
regex = "^[a-zA-Z0-9]$"
string = "default value"

[secret]
list = "_REDACTED_"
regex = "_REDACTED_"

[test.this.is.a]
range = "[0..100]"

[test.this.date.is.nested]
deep = "2019-10-22T04:26:10.654541"

[test.this.timediff.is.in.this]
branch = "0:00:10"

You can generate a reference configuration from a config object. This reference contains all available configuration options. If a default was specified for an entry it will be used, otherwise the example value.

from container_app_conf.util import generate_reference_config
config = AppConfig()
reference_config = generate_reference_config(config._config_entries.values())

This will return a dictionary representing the config entry tree. You can also specify a formatter and write a reference config to a file using:

from container_app_conf.util import write_reference
from container_app_conf.formatter.yaml import YamlFormatter
config = AppConfig()
write_reference(config, "/home/markus/.config/example.yaml", YamlFormatter())

If the generated reference contains values that do not make sense because of application constraints, specify your own example or better yet default value using the respective config entry constructor parameter.

If none of the existing types suit your needs you can easily create your own by extending the ConfigEntry base class.

A default value can be specified for every ConfigEntry by using the default constructor parameter.

By default config entries with a default different from None are required. A None value is only allowed for an entry if it has no default (or it is set to None explicitly).

For required entries it is not possible to set its value None even after initial parsing. Omitting a value for this entry in all data sources will result in an exception.

If an entry requires a value and has no default, set the required constructor parameter to True.

If you want to allow setting a None value even if the default value is not None, you have to explicitly set required=False.

If your config contains secret values like passwords you can mark them as such using the secret=True constructor parameter. That way their value will be redacted when printing the current configuration.

container-app-conf supports the simultaneous use of multiple data sources to determine configuration values. The following implementations are available:

Since you only specify the key path of a config entry the ENV key is generated automatically by concatenating all key path items using an underscore, converting to uppercase and replacing any remaining hyphens also with an underscore:

key_path = ["my_app", "my-example"]

would yield MY_APP_MY_EXAMPLE.

Multiple data sources using the filesystem are available:

• YamlSource
• TomlSource
• JsonSource

By default config files are searched for in multiple directories that are commonly used for configuration files which include:

• ./
• ~/.config/
• ~/

This can be customized using the path constructor parameter:

from container_app_conf.source.yaml_source import YamlSource
yaml_source = YamlSource(file_name="myapp", path=["/my/path", "/my/other/path"])

By default every Config subclass instance will behave like a singleton. This means if you change the config value in one instance it will also affect all other instances of the same __class__.

To be able to create multiple instances of a config that are independent of one another this behaviour can be disabled using the singleton constructor parameter:

config1 = AppConfig(singleton=False)
config2 = AppConfig(singleton=False)

GitHub is for social coding: if you want to write code, I encourage contributions through pull requests from forks of this repository. Create GitHub tickets for bugs and new features and comment on the ones that you are interested in.

container-app-conf
Copyright (c) 2019 Markus Ressel

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