def double(x):

    # This is not what we want!
    x = x * 2
    
def double_fixed(x):
    # This is what we want
    
    return x * 2
    
if __name__ == '__main__':
    x = 27
    double(x)
    print x
    
    x = 99
    x = double_fixed(x)
    print x