python inheritance and __init__ functions

Question

I came across the folloqing type of code when looking for some pyQt examples :

class DisplayPage(QWizardPage):
    def __init__(self, *args):
        apply(QWizardPage.__init__, (self, ) + args)

What does *args mean ?
What is the purpose of using apply for this type of code ?

Answer 1

*args means that __init__ takes any number of positional arguments, all of which will be stored in the list args. For more on that, see What does *args and **kwargs mean?

This piece of code uses the deprecated apply function. Nowadays you would write this in one of three ways:

 QWizardPage.__init__(self, *args)
 super(DisplayPage, self).__init__(*args)
 super().__init__(*args)

The first line is a literal translation of what apply does (don't use it in this case, unless QWizardPage is not a new-style class). The second uses super as defined in PEP 367. The third uses super as defined in PEP 3135 (works only in Python 3.x).

Answer 2

DisplayPage inherits from QWizardPage. Its constructor accepts a variable amount of arguments (which is what *args means), and passes them all to the constructor of its parent, QWizardPage

It's better to say:

super(DisplayPage, self).__init__(*args)