Program class

The Program class has by default two attributes :

• historic: an array used to store every step of the program,

• worker:

Saving variables

An important method of the Program class is log. Everytime it is called, all variables of the program except the two previously mentionned are saved inside historic. Everytime something within the program happens, log is called to keep track of every changement.

Adding and modifying variables

When a user wants to keep track of a variable, he has to declare as an attibute of an instance of Program. For instance, the following code show how to declare and add the variable x of value 5 to a Program named p:

p.x = 5

In Python, new attributes can be freely created by simply affecting a value to it. When Python tries to the set a value of an attribute, it checks if the attribute exists. If it does, the value is simply changed, otherwise the attribute is created and its value set. This is done implicitly done with the __setattr__ method. Here, the method is overrided in order to do additionnal operations:

• Everytime __setattr__ is called, the log method is also called in order to take into account the new state of the whole program.

• The type of the value is checked in order to apply needed transformations (such as int or float into Number) and to raise en error if the type is not supported.

Accesing a value

Any attribute can easely be accessed via the usual way:

p.x

But behind the scene, the __getattr__ method is called. This method also save the state of the program by calling log.