error: expected an indented block, python

so, im following a course called Python Game Development™ : Build 11 Total Games.
and I came across an error saying expected an indented block and I don’t know how to fix it as the person who wrote the code has the same exact code as me. so, I don’t get whats wrong because they had no error, and I did.
this is my code:

import collections

import math

import os

def path(filename):

    filepath = os.path.realpath(__file__)

    dirpath = os.path.dirname(filepath)

    fullpath = os.path.join(dirpath,filename)

    return fullpath

def line(a,b,x,y):

    import turtle

    turtle.up()

    turtle.goto(a,b)

    turtle.down()

    turtle.goto(x,y)

class vector(collections.Sequence):

    PRECISION = 6

    __slots__ = ('_x','_y','_hash')

    def __init__(self,x,y):

        self._hash = None

        self._x = round(x,self.PRECISION)

        self._y = round(y,self.PRECISION)

    @property

    #getter

    def x(self):

        return self._x

    @x.setter

    def x(self,value):

        if self._hash is not None:

            raise ValueError('Cannot set x after hashing')

        self._x = round(value,self.PRECISION)

    @property

    def y(self):

        return self._y

    @y.setter

    def y(self,value):

        if self._hash is not None:

            raise ValueError('Cannot set y after hashing')

        self._y = round(value,self.PRECISION)

    def __hash__(self):

        

        if self._hash is None:

            pair = (self.x,self.y)

            self._hash = hash(pair)

        return self._hash

    def __len__(self):

        return 2

    def __getitem__(self,index):

        if index == 0:

            return self.x

        elif index == 1:

            return self.y

        else:

            raise IndexError

    def copy(self):

        type_self = type(self)

        return type_self(self.x,self.y)

    def __eq__(self,other):

        if isinstance(other,vector):

            return self.x == other.x and self.y == other.y

        return NotImplemented

    def __ne__(self,other):

        if isinstance(other,vector):

            return self.x != other.x and self.y != other.y

        return NotImplemented

    def __iadd__(self,other):

    def __add__(self,other):

the error is on def add(self,other):. I’m a beginner programmer. so if u could help me out with this error, it would be great. thank you

>Solution :

When you copied the code, you forgot to copy the the business logic in iadd and add, if you add that the error will disappear.

def __iadd__(self,other):
   # Your code goes here

def __add__(self,other):
   # Your code goes here

Note: Replace # Your code goes here with the actual business logic.