If I understand you correctly, you probably want something like

if x is None:
print "x has no value"

You can just do

import sys
sys.path.append('pythonpathhere')

you could just do

print "The location of the largest number is", (1+l1.index(max(l1))

or something similar

It would help if you wrapped your code in [CODE ] [/ CODE] tags

No, put code tags around the code in your post eg.
[code ]
#python code here
[/code ]

it is equal to 15 because you are passing b_var to the function

c_var = a_func(b_var)
you are getting mixed up between the a_var in the function and the other a_var

I would suggest going through the tuturials at docs.python.org

You could use exit(0)

I know this doesn't answer the question, but
Could you just use True and False keywords instead of Y and N?

Why did you import math near the middle of the code instead of the beginning?