You are using qty1 before you have assigned it.

Example:

def test():
    print(c);
    c = 'hello';
 

calling test() will result in your error. You can't print c before it is assigned.

This usually occurs when one uses same variable names in different scopes.

Example:

c = 'Hey!'

def test():
    print(c);

def test2():
    print(c);
    c = 'hello';

calling test() will work. The outer variable c will be used. Calling test2() will result in the error above, since the inner scope has its own variable c.

Regards.