With this dialog, the user can, by selecting classes from a categorized tree of classes derived from StepFuncVisitor, assemble a step function.
In a later version, the user will also be able to set arguments, such as the probability for nondeterministic visitors.
When the user activates a class in the list, insert it into the correct slot at the right.
Display the docstring of the class and its __init__ at the bottom of the window when a new class has been selected, or display a general help text when the user clicks on something else.
Taken from stackoverflow user Alex Martelli.