How to extract the value from a slider bar.

edit

sage: @interact

sage: def func(n = slider(0, 10, 1)):

sage: print("n: %s" %n)

This gives me a slider bar with corresponding value of n, how do I link this value of n directly to a list such as:

sage: n=7

sage: a_i=list(var('a_%d' %i)for i in range(0,n+1))

sage: show(a_i)