Actually the issue is that the description doesn't define that position (x,y) means column x, row y. (I assumed the opposite, since that's more natural for me.)

valid_braces("((")==true because braces contains only open braces and its size is even.

@metalim is correct

The order "y, x, v" is correct.

I think the descrption of

'p' A "put" call (a way to store a value for later use). Pop y, x and v, then change the character at the position (x,y) in the program to the character with ASCII value v

is incorrect.

Pop y, x and v

should be Pop x, y and v.:)