yakonfig 0.7.7

load a configuration dictionary for a large application

yakonfig
========

yet another config management library, or a yak on a fig

Yakonfig parses a YAML configuration file at application startup, and makes parts of that configuration available to modules within the application. It is intended for multi-module applications where each module needs a separate configuration. The Yakonfig library merges application-provided default configuration, a user-provided configuration file, and command-line options to produce a unified global configuration.

yakonfig API
------------

Applications using Yakonfig generally create an ``argparse.ArgumentParser`` object and call ``yakonfig.parse_args()``, giving it a list of configurable modules or other items. A typical application setup looks like:

```python
import argparse
import dblogger
import kvlayer
import yakonfig

def main():
parser = argparse.ArgumentParser()
yakonfig.parse_args(parser, [yakonfig, dblogger, kvlayer])
...

if __name__ == '__main__':
main()
```

The application will include ``--help``, ``--config FILE``, and ``--dump-config MODE`` flags by default; modules can provide additional command-line arguments.

The module list passed to ``parse_args()`` is a list of objects that look similar to ``yakonfig.Configurable`` objects. They can be actual objects, typically factories, or they can be classes or even Python modules that happen to include the same names. A top-level Python module might look like:

```python
import a_package.submodule

#: Name of this module in the config file
config_name = 'a_package'
#: Inner blocks within this configuration
sub_modules = [a_package.submodule]
#: Default configuration
default_config = {'random_number': 17}
```

The objects contained in the ``sub_modules`` list have the same format. Running ``./my_program.py --dump-config=default`` would print out a YAML file:

```yaml
a_package:
random_number: 17
submodule: ...
```

A typical pattern is to create a factory object that has many configurable objects within it, such as stages in a data-processing pipeline. The ``yakonfig.factory.AutoFactory`` class supports this pattern. Objects built by the factory do not declare any of the configuration metadata; instead, Yakonfig determines the configuration name and default configuration by inspecting the object's constructor, or the function's argument list. The factory class itself needs to include the standard configuration metadata.

```python
class a_stage(object):
def __init__(self, random_number=17):
self.random_number = random_number
def __call__(self):
print self.random_number

class StageFactory(yakonfig.factory.AutoFactory):
config_name='stage_factory'
auto_config=[a_stage]
def __call__(self):
stage = self.create(a_stage)
stage()
```

The corresponding default YAML configuration:

```yaml
stage_factory:
a_stage:
random_number: 17
```

See [tests](src/tests/yakonfig/test_yakonfig.py) for further illustrations.