container-app-conf

container-app-conf

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 :)

How to use

Install dependency

pip install container-app-conf

Extend ConfigBase base

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)

Use configuration values

config = AppConfig()

value = config.MY_CONFIG.value

Print current config

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"

Generate reference config

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.

Config Types

Name	Description	Type
BoolConfigEntry	Parses bool, int (0 and 1) and str values (yes, no etc.) to a boolean value	bool
IntConfigEntry	Parses input to an integer	int
FloatConfigEntry	Parses input to a floating number	float
RangeConfigEntry	Parses input to a range (see py-range-parse)	Range
StringConfigEntry	Takes the raw string input	str
RegexConfigEntry	Parses and compiles regular expressions	re.pattern
DateConfigEntry	Parses various datetime formats (see python-dateutil)	datetime
TimeDeltaConfigEntry	Parses various timedelta formats (see pytimeparse)	timedelta
FileConfigEntry	Parses a file path	Path
DirectoryConfigEntry	Parses a directory path	Path
DictConfigEntry	Parses a dictionary	dict
ListConfigEntry	Parses a comma separated string to a list of items specified in another ConfigEntry (in yaml it can also be specified as a yaml list)	[]

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

Default Values

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

Required values

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.

Secret values

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.

Data sources

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

Name	Description
EnvSource	Reads environment variables
YamlSource	Parses YAML files
TomlSource	Parses TOML files
JsonSource	Parses JSON files

EnvSource

ENV Key

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.

Filesystem Source

Multiple data sources using the filesystem are available:

• YamlSource
• TomlSource
• JsonSource

File paths

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"])

Singleton

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)

Contributing

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.

License

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

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.