appsettings2

A python library that unifies configuration sources into a Configuration object that can be bound to complex types, or accessed directly for configuration data.

It can be installed from PyPI through the usual methods.

This README is a high-level overview of core features. For complete documentation please visit https://appsettings2.readthedocs.io/.

Quick Start

Using appsettings2 is straightforward:

1. Construct a ConfigurationBuilder object.
2. Add one or more ConfigurationProvider objects to it.
3. Call build(...) to get a Configuration object populated with configuration data.

from appsettings2 import *
from appsettings2.providers import *

config = ConfigurationBuilder()\
    .add_provider(JsonConfigurationProvider(f'appsettings.json'))\
    .add_provider(JsonConfigurationProvider(f'appsettings.Development.json', required=False))\
    .add_provider(EnvironmentConfigurationProvider())\
    .build()

print(config)

In the above example two JSON Configuration Providers are added to the builder. The first will fail if "appsettings.json" is not found, the second will succeed whether or not the "appsettings.Development.json" exists (because required=False). This allows for an optional development configuration to exist on development workstations without requiring a code change.

A third Configuration Provider is also added, an EnvironmentConfigurationProvider, which allows configuration to be loaded from Environment Variables.

The order of providers determines precedence of configuration data. Providers added last will take precedence over providers added first. Values which are not provided by later registrations will not override values provided by earlier registrations.

Given the example above, this means that configuration data provided via Environment Variables will override configuration data provided via JSON files.

Accessing Configuration Data

There are multiple ways of accessing Configuration data:

• Using dynamic attributes which represent your configuration data.
• Using configuration keys by calling get(...) and set(...) methods.
• A dictionary-like interface exposing configuration data via indexer syntax.
• Binding the configuration data to a class/object you define.

Direct Access via Configuration object

Consider the following code which demonstrates the first three methods mentioned above. All three of these methods are equivalent and return the same underlying value.

# access `Configuration` attributes
value = configuration.ConnectionStrings.SampleDb
# access using `get(...)`
value = configuration.get('ConnectionStrings__SampleDb')
value = configuration.get('ConnectionStrings:SampleDb')
value = configuration.get('ConnectionStrings').get('SampleDb')
# access using indexer
value = configuration['ConnectionStrings__SampleDb']
value = configuration['ConnectionStrings:SampleDb']
value = configuration['ConnectionStrings']['SampleDb']

When accessing hierarchical data by "key" you can use a double-underscore delimiter or a colon delimiter, they are equivalent.

Devs and Ops from different walks will likely prefer one form over the other, so both are supported.

Additionally, keys are case-insensitive (attribute names are not.)

Binding Configuration to Objects

It's possible to bind configuration data to complex types. While some of the implementation is currently naive, it should work well for the vast majority of use cases. If you find your particular case does not work well please reach out to me and I will work with you to implement a sensible solution. Consider the following Python code:

json = """{
  "ConnectionStrings": {
    "SampleDb": "my_cxn_string"
  },
  "EnableSwagger": true,
  "MaxBatchSize": 100
}"""

class ConnStrs:
    """An ugly class name to demonstrate the class name does not matter."""
    SampleDB: str

class AppSettings:
    ConnectionStrings: ConnStrs
    EnableSwagger: bool
    MaxBatchSize: int

configuration = ConfigurationBuilder()\
    .add_provider(JsonConfigurationProvider(json=json))
    .build()

settings = AppSettings()
configuration.bind(settings)

print(settings.ConnectionStrings.SampleDB) # prints "my_cxn_string"

The resulting settings object will contain all of the configuration data properly typed according to type hints.

It is also possible to bind to a subset of a configuration, building upon the above, consider the following:

connectionStrings = configuration.bind(ConnStrs(), 'ConnectionStrings')
print(connectionStrings.SampleDB)

Lastly, a cautious eye may have noticed that the input configuration and class definition have a casing difference. SampleDb vs SampleDB -- by design binding is case-insensitive. This ensures that automation/configuration systems which can only communicate in upper-case can be used to populate complex objects which follow a strict naming convention without burdening devs/devops with extra work.

Accessing Configuration Dictionary-like

Configuration is dict-like and in most cases can be used as if it were a dict where strict type checks would not otherwise prevent it.

Transform Configuration to Dictionary

You can transform a Configuration instance into a dictionary (as a copy.) If you have some chunk of code that can consume a dictionary but can't consume a Python object (it happens) then you can get at a proper dictionary instance as follows:

configuration = builder.build()
d = configuration.to_dict()
print(d)

Providers

• Command-Line args, via CommandLineConfigurationProvider.
• Environment variables, via EnvironmentConfigurationProvider.
• JSON, via JsonConfigurationProvider.
• TOML, via TomlConfigurationProvider.
• YAML, via YamlConfigurationProvider.

Custom Provider Development

You can implement custom Configuration Providers by subclassing ConfigurationProvider and implementing populate_configuration(...).

For a peek at the simplicity of provider implementation, this is ConfigurationProvider:

class ConfigurationProvider(abstract):

    @abstractmethod
    def populate_configuration(self, configuration:Configuration) -> None:
        """The ConfigurationProvider will populate the provided Configuration instance."""
        pass

Essentially, you read your configuration source and write the configuration data into the specified Configuration object. Much of the complexity in dealing with hierarchy and allocation is encapsulated within the impl of Configuration. As a result, most providers are less than 20 lines of functional code.

Helpers

There are several helpers available which simplify loading configurations. Consider the following example:

import appsettings2

config = appsettings2.get_configuration()

You can read more about get_configuration in the docs.

Contact

You can reach me on Discord or open an Issue on Github.