curriculum/challenges/english/blocks/learn-special-methods-by-building-a-vector-space/65f9dd6e5a08af19c196c2df.md
The vector resulting from the subtraction of one vector from another is obtained by calculating the difference of each of their components. For example, subtracting (2, 4) from (7, 3) generates a third vector (5, -1), where 5 is the difference between 7 and 2 and -1 is the difference between 3 and 4.
As you did before inside the __add__ method, declare a kwargs variable after the if statement. Assign it a dictionary comprehension that iterates through the object attributes and creates a key-value pair for each key i, where the key is the same key as the current iteration and its value is the difference between the values of the i attributes of two operands.
You should declare a variable kwargs and assign it a dictionary comprehension that iterates over the object attributes.
({ test: () => assert(runPython(`
node = _Node(_code).find_class("R2Vector").find_function("__sub__").find_variable("kwargs").find_comp_iters()[0]
node.is_equivalent("vars(self)") or node.is_equivalent("self.__dict__")`)) })
The dictionary comprehension assigned to kwargs should use the variable i to iterate over the object attributes.
({
test: () => assert(runPython(`
_Node(_code).find_class("R2Vector").find_function("__sub__").find_variable("kwargs").find_comp_targets()[0].is_equivalent("i")
`))
})
The dictionary comprehension assigned to kwargs should use i as the key.
({ test: () => assert(runPython(`_Node(_code).find_class("R2Vector").find_function("__sub__").find_variable("kwargs").find_comp_key().is_equivalent("i")`)) })
The dictionary comprehension assigned to kwargs should assign the difference between the i attribute of self and the i attribute of other to the i key for each i.
({ test: () => assert(runPython(`
node = _Node(_code).find_class("R2Vector").find_function("__sub__").find_variable("kwargs").find_comp_expr()
node.is_equivalent("getattr(self, i) - getattr(other, i)") or node.is_equivalent("self.__getattribute__(i) - other.__getattribute__(i)")
`)) })
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)
--fcc-editable-region--
def __sub__(self, other):
if type(self) != type(other):
return NotImplemented
--fcc-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(f'v1 = {v1}')
print(f'v2 = {v2}')