Learn Special Methods by Building a Vector Space - Step 52

Python
1

Tell us what’s happening:

I have written following code:
def mul(self, other):
if isinstance(other, int) or isinstance(other, float):
kwargs = {i: ( other * getattr(self, i) ) for i in vars(self)}
return self.class(**kwargs)

but it doesn’t pass.
Hint tells me that - You should return a new instance of the current class only when the type of other is either int of float.

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

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

    def __repr__(self):
        arg_list = [f'{key}={val}' for key, val in vars(self).items()]
        args = ', '.join(arg_list)
        return f'{self.__class__.__name__}({args})'

    def __add__(self, other):
        if type(self) != type(other):
            return NotImplemented
        kwargs = {i: getattr(self, i) + getattr(other, i) for i in vars(self)}
        return self.__class__(**kwargs)

    def __sub__(self, other):
        if type(self) != type(other):
            return NotImplemented
        kwargs = {i: getattr(self, i) - getattr(other, i) for i in vars(self)}
        return self.__class__(**kwargs)

# User Editable Region

    def __mul__(self, other):
        if isinstance(other, int) or isinstance(other, float):
            kwargs = {i: ( other * getattr(self, i) ) for i in vars(self)}
            return self.__class__(**kwargs)

# 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 = R2Vector(x=0.5, y=1.25)
print(f'v1 = {v1}')
print(f'v2 = {v2}')
v3 = v1 + v2
print(f'v1 + v2 = {v3}')
v4 = v1 - v2
print(f'v1 - v2 = {v4}')
v5 = v1 * 3
print(v5)
v6 = R3Vector( x=12, y=23, z=34)
print(v6)

v7 = v6 * ''
print(v7)

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Challenge Information:

Learn Special Methods by Building a Vector Space - Step 52

2

Try to use type() instead of isinstance().

3 Likes
3

if type(other) in (int, float):

It worked thanks

4 Likes
4 
 def __mul__(self, other):
        if type(other) in (int, float) : 
            kwargs = {i: getattr(self, i) * getattr(other, i) for i in vars(self)}
            return self.__class__(**kwargs)
        else : 
            return NotImplemented

I don’t understand the answer -
type(other) resolves to R2Vector - will never be int or float.,never resolve to true.
The return must be return self.class(**kwargs).
Don’t know verify that the vars, x and y in this case are both float or int.
besides it is not an acceptable answer.
response: “Sorry, your code does not pass. You’re getting there.”
Not good at python and confused as s*t

5

‘other’ here is not another object, instead, it might be an int or float (hence the conditional above). So, u don’t need to apply getattr to ‘other’:

kwargs = {i: getattr(self, i) * other for i in vars(self)}
6

start with the big issue. The following code does not pass the code check.

This is what I’m not understanding about this exercise. The issue of ‘other’ being a class or numeric type.

If I’m writing an overload to multiply an int with a class then the code works.
v1 = R2Vector(x=2, y=3)
v3= v1 * 2

If the multiplier overload is to multiply two instances of the same class. As we create the __add or __sub methods . This will never work.
Since ‘other’ is a class, not float or int.
v1 = R2Vector(x=2, y=3)
v2 = R2Vector(x=5, y=6)
v3= v1 * v2

So I’m stuck, not being able to pass the step, and confused.

7

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