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17.10: Debugging

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  • It is legal to add attributes to objects at any point in the execution of a program, but if you have objects with the same type that don’t have the same attributes, it is easy to make mistakes. It is considered a good idea to initialize all of an object’s attributes in the init method.

    If you are not sure whether an object has a particular attribute, you can use the built-in function hasattr (see Section 15.7).

    Another way to access attributes is the built-in function vars, which takes an object and returns a dictionary that maps from attribute names (as strings) to their values:

    >>> p = Point(3, 4)
    >>> vars(p)
    {'y': 4, 'x': 3}

    For purposes of debugging, you might find it useful to keep this function handy:

    def print_attributes(obj):
        for attr in vars(obj):
            print(attr, getattr(obj, attr))

    print_attributes traverses the dictionary and prints each attribute name and its corresponding value.

    The built-in function getattr takes an object and an attribute name (as a string) and returns the attribute’s value.

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