Rounding integers?

Question

Why is the result of
x = 4.9999999999999999
y = int(x)
print(y)
5
but the result of
x = 4.999999999999999
y = int(x)
print(y)
4
?

Edit: Second question: Is there one single thing you can use instead of int() to work only with mathematically correctly rounded numbers? (I know I could google it, but I'm taking it easy with Sololearn course. tnx in advance).
Edit2: So now I know round() exists.
z = round(x)
print(z) = 5

Answer 1

It's a matter of floating point precision. Python deals 17 significant digits after floating point.
https://docs.python.org/3/tutorial/floatingpoint.html

Answer 2

If you want rounding, and not truncation, why aren't you using round()?