You are giving the object.__getattribute__() handler a signal that the attribute doesn't exist by raising an AttributeError. The defined behaviour is to then call __getattr__ instead. The exception is lost, it was handled by __getattribute__. From the documentation:

Called unconditionally to implement attribute accesses for instances of the class. If the class also defines __getattr__(), the latter will not be called unless __getattribute__() either calls it explicitly or raises an AttributeError.

If you don't want __getattribute__ to handle the exception, you need to move your __getattr__ behaviour over to a custom __getattribute__ method instead:

class A(object):
    @property
    def test(self):
        raise AttributeError('message which should not be lost')
        return 'this would never return'

    def __getattribute__(self, name):
        try:
            value = super(A, self).__getattribute__(name)
        except AttributeError as ae:
            # chance to handle the attribute differently
            # if not, re-raise the exception
            raise ae

Note that the hasattr() function behaves the same way; it'll return False when an exception is raised when trying to access the attribute.

This happens because the scipy module doesn't have any attribute named sparse. That attribute only gets defined when you import scipy.sparse.

Submodules don't automatically get imported when you just import scipy; you need to import them explicitly. The same holds for most packages, although a package can choose to import its own submodules if it wants to. (For example, if scipy/__init__.py included a statement import scipy.sparse, then the sparse submodule would be imported whenever you import scipy.)