Learn Special Methods by Building a Vector Space - Step 23

Python
1

Tell us what’s happening:

At first my code was:

def __str__(self):
    return str(tuple(getattr(self, i) for i in vars(self)))

But I got an error with no other indication than “You should return a generator expression using vars(self)”

So I removed the str() and tuple() functions to only return the generator object:

return (getattr(self, i) for i in vars(self))

Now it says “Your code raised an error before any test could run”. I checked the following task and it is literally displaying my later option.

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 (getattr(self, i) for i in vars(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())
print(v1)

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Challenge Information:

Learn Special Methods by Building a Vector Space - Step 23

1 Like
2

when it says this you have the error in the terminal, what does the terminal say?

3

from here, why do you have the tuple function?

4

It raises a TypeError with the message ‘str returned non-string (type generator)’. I already tried putting it in an str() call. It prints <generator object R2Vector.str.. at 0x1107fa8>, but still doesn’t pass the tests.

5

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

You want to return a generator function, not a string and not a tuple. Look at the hint it gives you:

You should return a generator expression that iterates over vars(self).

You had the correct code in your OP. You might have accidentally changed some other part of the code. I would reset it and try that return line again

6

the instructions from step 9 are valid here too

7

You’re right. I added a print() at the end of my code to visualize the output, but since the _str_ method was incomplete (not returning a string), it was raising an error. Everything worked fine after I removed the print.

1 Like
8

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