Symbolic accumulation

With Maple I can write seq(add(a[i], i=0..n), n=0..3); and get a[0], a[0]+a[1], a[0]+a[1]+a[2], a[0]+a[1]+a[2]+a[3] (*) If I write in Sage for n in range(4): add(a[i] for i in range(n)) I get the NameError: global name 'a' is not defined. If I first introduce the variable by a = var('a') then I get the TypeError: 'sage.symbolic.expression.Expression' object does not support indexing. How can I get the line (*) with Sage? Edit: This works: f=function('f') [add(f(i) for i in (0..n)) for n in (0..3)] gives [f(0), f(1) + f(0), f(2) + f(1) + f(0), f(3) + f(2) + f(1) + f(0)] So what I want is an equivalent for lists. a=list('a') [add(a[i] for i in (0..n)) for n in (0..3)]