Cognate - Related to the Same Common Root¶
Cognate is a package to make development of configurable component services easy to implement. Configurable here pertains to options settings, logging configuration, and service naming. Component here means the creation of isolated bits of code with well defined configuration and interfaces.
To be less cryptic, lets demonstrate the HelloWorld example. To begin, create a component service class:
from cognate.component_core import ComponentCore
import sys
class HelloWorld(ComponentCore):
def __init__(self, name='World', **kwargs):
self.name = name
super(HelloWorld, self).__init__(**kwargs)
def cognate_options(self, arg_parser):
arg_parser.add_argument(
'--name',
default=self.name,
help='Whom will receive the salutation.')
def run(self):
self.log.info('Hello %s', self.name)
if __name__ == '__main__':
argv = sys.argv
service = HelloWorld(argv=argv)
service.run()
The HelloWorld class defines a property name that will be used to
construct the log output during execution of the run method. The
cognate_options method is used to declare any attributes of the service
utilizing an argparse.ArgumentParser instance passed as the arg_parser
parameter. Child classes of ComponentCore can use all the features of the
python argparse.ArgumentParser, and these will be automatically mapped to
attributes of the same name for a given service instance.
With the HelloWorld component service above, the complete service features
can be demonstrated with the listing of the service usage. As in:
/cognate > python example/hello_world.py -h
usage: hello_world.py [-h] [--service_name SERVICE_NAME]
[--log_level {debug,info,warn,error}]
[--log_path LOG_PATH] [--verbose] [--name NAME]
optional arguments:
-h, --help show this help message and exit
--service_name SERVICE_NAME
This will set the name for the current instance.
This will be reflected in the log output.
(default: HelloWorld)
--log_level {debug,info,warn,error}
Set the log level for the log output. (default: error)
--log_path LOG_PATH Set the path for log output. The default file created
is "<log_path>/<service_name>.log". If the path
ends with a ".log" extension, then the path be a
target file. (default: None)
--verbose Enable verbose log output to console. Useful for
debugging. (default: False)
--name NAME Whom will receive the salutation. (default: World)
Note how ComponentCore adds the features for app naming, log configuration
and output. Also folded in, is the configuration option for the name
that is provided by the HelloWorld class.
Simply running python example/helloworld.py will cause silent execution as
default log_level is error. In addition, the logging output is silent,
as the verbose option is False.
To demonstrate HelloWorld with output, run:
/cognate > python example/hello_world.py --verbose --log_level info
MainThread:2014-08-02 13:30:57,988 -HelloWorld - INFO -- Logging configured for: HelloWorld
MainThread:2014-08-02 13:30:57,988 -HelloWorld - INFO -- Component service configuration complete with argv: Namespace(log_level='info', log_path=None, name='World', service_name='HelloWorld', verbose=True)
MainThread:2014-08-02 13:30:57,989 -HelloWorld - INFO -- Hello World
Note the setting of the verbose flag to enable logging output to console. In addition, the log_level flag is set to info, to enable logging output of the HelloWorld execution.
The ComponentCore will map arg_parser defined options to an attribute name and apply that value to the service instance. In the HelloWorld example, the arg_parser –name option is mapped to the self.name attribute. The net effect is to allow configuration of the service via command line args, as in:
/cognate > python example/hello_world.py --verbose --log_level info --name Dog
MainThread:2014-08-02 13:30:16,022 -HelloWorld - INFO -- Logging configured for: HelloWorld
MainThread:2014-08-02 13:30:16,022 -HelloWorld - INFO -- Component service configuration complete with argv: Namespace(log_level='info', log_path=None, name='Dog', service_name='HelloWorld', verbose=True)
MainThread:2014-08-02 13:30:16,022 -HelloWorld - INFO -- Hello Dog
A benefit to defining component services with ComponentCore is the ability to utilize the component as an instance. For example:
from hello_world import HelloWorld
# Configure with argv string
argv = '--verbose --log_level info --service_name CatWorld --name Cat'
hello_cat = HelloWorld(argv=argv)
# Configure with parameters
hello_dog = HelloWorld(verbose=True,
log_level='info',
service_name='DogWorld',
name='Dog')
hello_cat.run()
hello_dog.run()
The script above demonstrates how the component service can be configured utilizing a string passed via the argv parameter, as well as being instantiated via direct parameter passing. The script above would give output such as:
/cognate > python example/hello_script.py
MainThread:2014-08-02 13:32:11,237 -CatWorld - INFO -- Logging configured for: CatWorld
MainThread:2014-08-02 13:32:11,237 -CatWorld - INFO -- Component service configuration complete with argv: Namespace(log_level='info', log_path=None, name='Cat', service_name='CatWorld', verbose=True)
MainThread:2014-08-02 13:32:11,237 -DogWorld - INFO -- Logging configured for: DogWorld
MainThread:2014-08-02 13:32:11,237 -DogWorld - INFO -- Component service configuration complete with argv: Namespace(log_level='info', log_path=None, name='Dog', service_name='DogWorld', verbose=True)
MainThread:2014-08-02 13:32:11,238 -CatWorld - INFO -- Hello Cat
MainThread:2014-08-02 13:32:11,238 -DogWorld - INFO -- Hello Dog
The ability to treat component services as isolated code with well defined interfaces make reuse of components much easier, as well as usage in multi-threaded environments.
Be sure to checkout Getting Started with Cognate to delve into all the goodness.
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