Why those codes?

Question

Why this code work
x="3"
y="3"
z=int(x)+int(y)
print(z)
And this doesn't work
x="3"
y="3"
z=(x)+(y)
print(z)
And why this work
print(num:=int(input())
And this doesn't
print(num:=(input())
and what is the (int) and what it means and when must I put it 🤔

Answer 1

input() always returns string and "3" is also a string, so if you want to sum numbers, you need to convert them to a numeric data type. For instance to integer using int()