I have the following class:

```
class C3DPoint(object):
    def __init__(self, x, y, z):
        self.x = x
        self.y = y
        self.z = z

    # Other methods

```

I want to be sure that if somebody sets `v3dpoint.x = <sth>` it throws an error in case vale is not string.

How can this be done?