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When you start working with objects, you are likely to encounter some new exceptions. If you try to access an attribute that doesn’t exist, you get an
>>> p = Point() >>> p.x = 3 >>> p.y = 4 >>> p.z AttributeError: Point instance has no attribute 'z'
If you are not sure what type an object is, you can ask:
>>> type(p) <class '__main__.Point'>
You can also use
isinstance to check whether an object is an instance of a class:
>>> isinstance(p, Point) True
If you are not sure whether an object has a particular attribute, you can use the built-in function
>>> hasattr(p, 'x') True >>> hasattr(p, 'z') False
The first argument can be any object; the second argument is a string that contains the name of the attribute.
You can also use a
try statement to see if the object has the attributes you need:
try: x = p.x except AttributeError: x = 0
This approach can make it easier to write functions that work with different types; more on that topic is coming up in Section 17.9.