im having trouble figuring out how this nested functions get the values. can someone pls explain it to me. the code works btw

Question

im having trouble figuring out how this works. can someone pls explain it to me. the code works btw.

def foo(x, y):

def goo(x, y):

    x = 2*x

    y = 3*y

    z = x+y

    print('x =', x, '; y =', y, '; z =', z)

    return z


def hoo(x, y):

    x = x//2

    y = y//3

    z = x+y

    print('x =', x, '; y =', y, '; z =', z)

    return z


z = hoo(x,y) + goo(y,x)

print('x =', x, '; y =', y, '; z =', z)

return z


x = 10

y = 20

z = 30

print('x =', x, '; y =', y, '; z =', z)

z = foo(x,y)

print('x =', x, '; y =', y, '; z =', z)

Answer 1

To understand how a code works, just follow the functions.

foo is called. Since integer types are immutable (wikipedia) in foo(x,y) x and y are copies of the x and y you gave as parameters.

In python expression are evaluated from left to right therefore.

First function hoo is called (same remark about parameters) the value of x and y are changed and z is computed you get ('x =', 5, '; y =', 6, '; z =', 11) and the value z (11) is returned.

Once outside hoo function x and y at this level are respectively 10 and 20 because they were not changed (immutable thing… see above) . Then function goo is called. (same remark about parameters) (warning you enter y for parameter x of goo and x for parameter y of goo) the value of x and y are changed and z is computed you get ('x =', 40, '; y =', 30, '; z =', 70) and the value z (70) is returned.

Once outside goo function x and y at this level are respectively 10 and 20 because they were not changed (immutable thing… see above).

The sum function between the two values returned by hoo and goo is done. z= 11 + 70. you get ('x =', 10, '; y =', 20, '; z =', 81) and z is returned.

Then outside foo function. x and y at this level are respectively 10 and 20 because they were not changed (immutable thing… see above) . z is given the value of the return function foo therefore z=81

And you get ('x =', 10, '; y =', 20, '; z =', 81)