Problem with local variable. NameError: name 'b' is not defined in python

Question

There is something wrong with my code. I still don't understand how local variable works. The following is an example of a simple code. And I have a NameError issue. Why? How can I fix this? I need to fix this error without Global variables! And there must be variable(a) ! What should I do for the answer of this code to come out 21?

def first(a):
    a = 0
    b = 3
    return b
def second(a):
    a = 0
    j = 7
    return j
def result():
    return first(b) * second(j) # <-NameError: name 'b' is not defined in python 
print(result())

Answer 1

You should define what does your b and j mean in string 10: For python you are giving noting to function, but this function is asking for some value (a), it should be like this:

def first(a):
    a = 0
    b = 3
    return b
def second(a):
    a = 0
    j = 7
    return j
def result():
    b = 123 # Defining what are we giving to our functions
    j = 5

    return first(b) * second(j) # Now it will work
print(result())

So you can use b and j value, and access return values:

    b = 3
    return b

    j = 7
    return j

Think like this, when you're returning some value, it fully replaces function with that value.