baspl++ User Manual
Running baspl++

This section gives a brief overview of the different baspl++ objects.

All baspl++ objects have the following in common:

One advantage of the object-oriented approach is that multiple objects can be created for each class. This is illustrated with the following example:

The duality of the baspl++ objects - being accessible in the graphical user interface and from the Python environment at the same time - is illustrated with the following examples:

baspl++ objects have two elements that make part of the graphical user interface: a menu and an editor. When a baspl++ object is selected (usually via the tree widget in the main window), two things happen: First, the Object-> sub-menu in the main window is changed according to the selected object. Second, the editor of the object is activated in the editor area of the main window.

In the menu, the following actions are available for all baspl++ objects:

The object's editor allows to manipulate all settings of the object. In many cases, it displays additional information: For instance, a Field object contains the minimum and maximum values for the different components. These values are displayed in the editor for inspection. The Field editor allows also to browse over the different elements and nodes and to inspect the respective field values.

Most objects are listed in the tree widget in the main window. An object is selected by clicking on it with the left button of the mouse. With the right button of the mouse, the object is not only selected, but the object's menu appears as a context (pop-up) menu as well.

Objects that are displayed in a Scene object can be selected by clicking the right button of the mouse at the location inside the Scene window where the object in question is displayed. A context (pop-up) menu appears which allows to select the object(s).

The identifier of a baspl++ object is displayed in the tree widget in the main window. In the Python environment, it can be obtained via the id property. For instance, the identifier of default Scene object (which is referenced by the global variable s) is obtained

>>> print s.id

To change the identifier of an object from the graphical user interface, make sure that the object is selected and then select Object->Set Object ID... from the menu. A dialog appears where the new identifier can be entered.

To change the identifer of an object from the Python environment, assign the id property:

>>> s.id = 'New Identifier'

To make baspl++ objects created with the graphical user interface accessible from the Python environment, they must be referenced by Python variables.

The most straightforward way of achieving this is to select the object in the graphical user interface and then to select File->Assign to Python variable.... A dialog appears where the name of the global variable to be assigned to the object can be entered. If there are already global variables referencing that object, they are displayed in the same dialog. After that, the object is now additionally referenced by that variable.

Alternatively it is possible to retrieve the existing baspl++ objects by means of the find_object and find_objects functions.

Examples:

m = find_object('airfoil.mc')

assigns the (Model) object having the identifier "airfoil.mc" to the variable m. If the object does not exist, the Python value None is assigned instead.

parts = find_objects(NPart)

assigns the current list of all instances of class NPart to the variable parts.

baspl++ objects have to be deleted by means of the delete function. In the graphical user interface, this can be done by first selecting the object and then activating the Object->Delete item in the main menu. In the Python environment, the object must be referenced by a variable (e.g. o). It is deleted by calling the delete function:

>>> o.delete()

The delete function is a special feature of baspl++ objects. Ordinary Python objects are deleted as soon as they are not referenced anymore. But baspl++ objects are always referenced by the application itself; this is necessary for the proper functioning of the graphical user interface (the tree widget, the menus, the editor area, etc.). By calling the delete function, baspl++ is told that all references to this object should be removed. Another purpose of the delete function is to free all internal memory structures. Thus, after calling the delete function, the object cannot be used anymore.

In the remainder of this section, the concept of references is briefly explained.

The concept of references is used by many programming languages, such as Java and Python. What is a reference? In Python, all objects are accessed by reference. That is, the variables are not the objects themselves, instead a variable points to, or better, refers to the object (hence reference). This way, there may be many variables referring to the same object (this is also known as "aliasing").

Example:

>>> a = [1, 2]   # create a list object [1, 2] and reference it by 'a'
>>> print a
[1, 2]
>>> b = a        # create a new reference to the same list object
>>> a.append(3)  # modify the list object by appending the number 3
>>> print b      # 'b' references the same list object
[1, 2, 3]
>>> del a        # delete the reference 'a' (not the list object)
>>> print b      # 'b' is still valid
[1, 2, 3]

Objects remain as long as they are referenced. In the example above, the list object remains because it is still referenced by b. If you issue

del b

no reference to the list object remains and its destructor function is called (in case of cyclic references, these will evenutally be detected by Python's automatic garbage collector, and the destructor function is called during a collection run).