# Learn Special Methods by Building a Vector Space - Step 74

### Tell us what’s happening:

I have tried the dictionary comprehension method for all x, y and z points. As you can see creating x, y and z values using equals operator. I believe this would give me the appropriate outcome. I don’t know why it’s wrong

``````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})'

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)

def __mul__(self, other):
if type(other) in (int, float):
kwargs = {i: getattr(self, i) * other for i in vars(self)}
return self.__class__(**kwargs)
elif type(self) == type(other):
args = [getattr(self, i) * getattr(other, i) for i in vars(self)]
return sum(args)
return NotImplemented

def __eq__(self, other):
if type(self) != type(other):
return NotImplemented
return all(getattr(self, i) == getattr(other, i) for i in vars(self))

def __ne__(self, other):
return not self == other

def __lt__(self, other):
if type(self) != type(other):
return NotImplemented
return self.norm() < other.norm()

def __gt__(self, other):
if type(self) != type(other):
return NotImplemented
return self.norm() > other.norm()

def __le__(self, other):
return not self > other

def __ge__(self, other):
return not self < other

# User Editable Region

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

def cross(self, other):
if type(self) != type(other):
return NotImplemented
kwargs = {x == getattr(self, y) * getattr(other, z) - getattr(self, y) * getattr(other, z) for x in vars(self)}
{y == getattr(self, z) * getattr(other, x) - getattr(self,x) * getattr(other,z) for y in vars(self)}
{z == getattr(self,x) * getattr(other, y) - getattr(self, y) * getattr(other,x) for z in vars(self)}

return self.__class__(**kwargs)

# User Editable Region

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 * v2
print(f'v1 * v2 = {v5}')
``````

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### Challenge Information:

Learn Special Methods by Building a Vector Space - Step 74

You have 3 separate dictionary comprehensions here, not just one. The first one is assigned to `kwargs` but the other two go nowhere.

This isn’t the correct syntax for a dictionary comprehension. Keep in mind `==` is a comparison operator, not an assignment.
https://www.geeksforgeeks.org/python-dictionary-comprehension/

Are you absolutely sure a dictionary comprehension is what’s needed here? I would probe the variables created in this object, print it out, see what it is and what it looks like.

Try to do a bit of exploring here before coding it up.

I would also look again at the formula and make sure you are keeping the order of the x, y and z variables the same.