Learn Special Methods by Building a Vector Space - Step 23

Python
1

Tell us what’s happening:

I don’t understand the instructions. How do I use getattr? And the help talking about vars(self) doesn’t help…

Your code so far


class R2Vector:
    def __init__(self, *, x, y):
        self.x = x
        self.y = y

    def norm(self):
        return sum(val**2 for val in vars(self).values())**0.5

# User Editable Region

    def __str__(self):
        return f'({", ".join(str(i) for i in getattr(self))})'


# User Editable Region

class R3Vector(R2Vector):
    def __init__(self, *, x, y, z):
        super().__init__(x=x, y=y)
        self.z = z

v1 = R2Vector(x=2, y=3)
v2 = R3Vector(x=2, y=2, z=3)
print(v1.norm())
print(v2.norm())

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Challenge Information:

Learn Special Methods by Building a Vector Space - Step 23

2

getattr() function is what you need. It takes an object as its first argument, and a string containing the attribute name as its second attribute.

So, getattr() will take 2 arguments: object, attribute

getattr(object, 'attribute')

Use vars(self) to iterate through the object attributes as you did in a previous step.

replacing the string returned by __str__() with a generator expression

You are still returning a string. Instead, you want to return a generator expression, which will be a comprehension in (parentheses)

3

Thank you! I was not sure about the return type. Often the steps are too many. It could be easier if several steps were grouped together.

4

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