How does the function that is called inside the class declaration?

Question

Have this code:

>>> class Foo:
...     zope.interface.implements(IFoo)
...
...     def __init__(self, x=None):
...         self.x = x
...
...     de         


        

Answer 1

Read the source, luke:

http://svn.zope.org/zope.interface/trunk/src/zope/interface/declarations.py?rev=124816&view=markup

def _implements(name, interfaces, classImplements):
    frame = sys._getframe(2)
    locals = frame.f_locals

    # Try to make sure we were called from a class def. In 2.2.0 we can't
    # check for __module__ since it doesn't seem to be added to the locals
    # until later on.
    if (locals is frame.f_globals) or (
        ('__module__' not in locals) and sys.version_info[:3] > (2, 2, 0)):
        raise TypeError(name+" can be used only from a class definition.")

    if '__implements_advice_data__' in locals:
        raise TypeError(name+" can be used only once in a class definition.")

    locals['__implements_advice_data__'] = interfaces, classImplements
    addClassAdvisor(_implements_advice, depth=3)