swap function output is different from what expected [duplicate]

Question

I think the output should be x = 5, y = 3. But, when I tried executing it in jes it shows that x=3 and y=5.

My swap function is as follows:

def swap (x,y):    
    temp=x
    x=y
    y=temp

And from my driver function I call swap():

def driver():    
    x=3
    y=5
    swap(x,y)
    print x
    print y

I want to know why isn't the output as expected?

Answer 1

Well this is not a big issue in python you can return multiple values like try this snippet it might help you.

def swap(a,b):
   return (b,a)

def driver(x,y):
    print "Previous x=",x,"y=",y
    x,y = swap(x,y)
    print "Now x=", x, "y=",y

driver(3,5)

Answer 2

As other answers have suggested, this really doesn't require functions. Since you have decided to use them though, you might as well try and understand a bit more about scopes.

In order to retain the swapped values you need to return them or else they get lost after the execution of swap():

def swap (x,y):
    temp=x
    x=y
    y=temp
    return x, y  # must return the swapped values.

Then, in the function where you call swap() you assign the returned values to the variables that you swapped:

def driver():
    x=3
    y=5
    x, y = swap(x,y)  # re-assign values
    print x
    print y

Running driver() now will give you the swapped value:

5
3

This happens because in the function swap() the variables x and y you pass as arguments are treated as local to that function, only swap can see their value. If you don't return this value back, it is lost and forgotten.