# mutable_args.py                                 David MacQuigg  ece175  5/7/08
'''
How to make primitive values mutable in Python.

You can wrap a primitive value in a mutable object, and modify the value via
attributes of the object.  A list [] is a convenient mutable object.
'''
def f(a, b):
    
    print "a = %s   b = %s" % (a, b)
    
    a += 1        # a now points to a local object.
    b[0] += 10    # b still points to the original object

    b.append('xyz')
    
    print "a = %s   b = %s" % (a, b)

def main():
    '''
    >>> main()
    x = 0   y = [0]
    a = 0   b = [0]
    a = 1   b = [10, 'xyz']
    x = 0   y = [10, 'xyz']
    '''
    x = 0; y = [0]  # a simple integer, and wrapped integer
    
    print "x = %s   y = %s" % (x, y)
    f(x, y)
    print "x = %s   y = %s" % (x, y)


from doctest import testmod
testmod(verbose=True)