curriculum/challenges/english/blocks/learn-special-methods-by-building-a-vector-space/666827a6fd0dbaafe8330ea6.md
__getattr__ is another special method that plays a role in accessing attributes.
The default implementation of __getattribute__ is to raise an AttributeError when the requested attribute is not an instance attribute or it is not present in the class tree.
In that case, __getattr__ is called if defined by the class. You can consider it as a sort of fallback when the usual attribute accessing procedure fails.
Turn the __getattribute__ method into __getattr__ and modify the string returned by the method into 'calling __getattr__'.
You should define a method named __getattr__ with two parameters, self and attr, inside the R2Vector class.
({ test: () => assert(runPython(`_Node(_code).find_class("R2Vector").find_function("__getattr__").has_args("self, attr")`)) })
Your __getattr__ method should return the string 'calling __getattr__'.
({ test: () => assert(runPython(`_Node(_code).find_class("R2Vector").find_function("__getattr__").has_return("'calling __getattr__'")`)) })
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})'
--fcc-editable-region--
def __getattribute__(self, attr):
return 'calling __getattribute__'
--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}', f'\nrepr = {repr(v1)}')
# print(f'v2 = {v2}', f'\nrepr = {repr(v2)}')
print(v1.x)
print(getattr(v1, 'x'))