Herne is a wrapper application that can be used to configure other applications.

The following example creates a simple "Hello World" app using Herne as the runner. Firstly we need to define the app using the HerneApp class as the template.

In a file my_first_app.py we add the following lines:

from Herne.AppBase import HerneApp
import copy

class HelloWorld(HerneApp):
    __version__ = 'v0.0.1'
    def __init__(self):
        HerneApp.__init__(self, 'HelloWorld')
        self._members = copy.deepcopy(HerneApp._members)
        self._members += ['UserName']
    
    def __call__(self):
        HerneApp.__call__(self)
        print("Hello {}!".format(self.UserName)

Firstly it the importance of using deepcopy when copying the _members property of HerneApp. Once we have copied this object we then assign additional properties relating to our app, in this example UserName is added which will provide the option for the user's name.

Secondly we redefine the __call__ method to additionally include what we would like the app to do, in this case simply greet the user.

Another requirement of Herne Apps is the declaration of a version label using __version__. Although this is not used beyond being printed it is useful when it comes to debugging in future.

To run your Herne App you will now need to define the options file for the run, these options can also be appended to the App script as a __main__ however it is recommended to code them seperately as this means you can have multiple options files for variety.

As an example, if the application HelloWorld has been developed and is found in its own directory greeting we can setup the Herne interface by creating placing the code above into a file greeting/Configurables.py. Say we want to greet a user "Dave", we would then make an options script to be read in at the same time:

from greeting.Configurables import HelloWorld

HelloWorld().UserName = 'Dave'

That's it! Now to run our application we use the included run script within Herne:

./run run_dave.py

(in the case of Windows python run run_dave.py) this would give the output:

===================================================================
                            test v0.0.1                            
                       Running on localhost                      
===================================================================
        
-------------------------------------------------------------------
INFO:Herne Runner	: OutputLevel : INFO
INFO:Herne Runner	: UserName : Dave
-------------------------------------------------------------------
INFO:Herne Runner	: Application Setup Successful.
Hello Dave!
INFO:Herne Runner	: Application Completed Successfully.

Note also it is possible to put the application code into a normal python script and create a new options script running both together:

./run hello.py run_dave.py

the contents of run_dave.py would then just be:

HelloWorld().UserName = 'Dave'

as the imports would be read directly from the application script itself.

The latest version of Herne now includes an app builder to simplify the process. The `AppBuilder' creates a python script containing a new app based on the users requirements:

AppBuilder(app_name, configurable_parameters, out_file=None, author=None, description=None)

By default the output file is the name of the app in lower case. An author name and description can be provided with the information also written to the script itself. The version of the app is automatically initialised to v0.1.0, it is recommended that you update this version number whenever the app is modified.

from Herne.AppBuilder import AppBuilder

AppBuilder('HelloWorld', ['UserName'], author='Joe Bloggs',
           description='Simple App to greet the user!', out_file='hello_world.py')

The generated script can then be modified with the author then adding all the methods they wish to call within the defined __call__ function within the created class. The script also contains a basic level of documentation.

The generated script would then be placed into the code folder for the module in development (Configurables.py here):

my_module
   |- my_module
   |     |_ Configurables.py
   |     |_ __init__.py
   |     |
   ..    ..