.. _importer_example:

Importer
========

|app| is a modular python framework for creating workflows that create data for SimCenter applications. In order to allow applications to be built **w/o the need to hard code every possible case** within if blocks, there is a class in |app| that will return the class given the class name. This is the **Importer** class. It's has one method, **get_class()**, which will return the python class with that given name from which an object can be instantiated. 

The following example shows a more typical python example. 

.. literalinclude:: classic.py
   :language: python
   :linenos:


The following example shows it re-written using the **Importer** class.

.. literalinclude:: importer.py
   :language: python
   :linenos:

To run for example the **importer.py** script for Berkeley, CA the following would be issued frm a terminal window:

.. code-block::
      
   python3 importer.py USA_FootprintScraper "Berkeley, CA"


and the application  would produce:

.. literalinclude:: output.txt
   :linenos:   
    
.. note::

   1. When constructing an **Importer** object, the constructor code automatically searches through all directories within the brails codebase to locate every available class. This setup allows developers to add their code seamlessly, without needing to modify this class.
   
   2. The purpose of the **Importer** class is to allow applications to be developed for building workflows. Consider developing an application that would parse the following JSON input file to such an application. By using the **Importer** class, this application can avoid a complex series of if-else statements to handle different types. Instead, it reads the type information and retrieves the appropriate class directly from the Importer. This approach is made possible because |app| is an object-oriented framework that leverages abstract base classes (ABCs), defined using Python’s abc module.

   .. literalinclude:: workflow.json
      :language: json		       
      :linenos:

   3. An additional advantage of this approach is that as developers add new subclasses, they do not have to search through the code to see all the places that need the if-else statements modified for their classes to be used.