''' Purpose: demonstrate a function side-effect in Python
'''

def f( x ) :
    ''' Does ???
    '''
    print( "start of f( x ):", id( x ) ) # this is the same as the id from the argument in up.py
    n = len( x )
    for i in range( 0, n ) :
        x[ i ] = 0 # modifying individual elements but not reassigning x
        print( "in for loop:", id( x ) )
    # when you reassign variables, you lose that original assignment, so if you're using a function to modify a list
    # that assignment can be lost by saying x = ...
    # there are times that we want to reassign

    # we are modifying our argument list because there is no assignment statement that updates the value of x
    x.append( 1112 )
    print( "end of f( x ):", id( x ) )

    return