Why is my function not being executed in python?

In the above code you call the function a which creates and sets a local variable x and defines a nested function, but that function is never called. As such you do not see any prints.

Note that just calling b() in a is not a good idea - as this function will recursively call itself with no stop condition. Instead you could write it as follows:

def a():
    x=20

    def b():
        global x
        x=88


    print("before calling b", x)
    b()
    print("after calling b", x)
a()

It seems like what you really want is this code:

def a():
    x=20

    def b():
        global x
        x=88

    print("before calling b",x)
    b()
    print("after calling b",x)

a()

This code tests the effect of calling b from within a on the values of a variable x, local to a. There will be no effect, as x is not global. The output would be:

before calling b 20
after calling b 20

If you change the definition of b to:

def b():
    nonlocal x
    x=88

You will see the effect of modifying x:

before calling b 20
after calling b 88