desolve?
EXAMPLES:
sage: x = var('x')
sage: y = function('y')(x)
sage: desolve(diff(y,x) + y - 1, y)
(_C + e^x)*e^(-x)
sage: x = var('x')
sage: y = function('y')(x)
sage: de = diff(y,x,2) - y == x
sage: desolve(de, y)
_K2*e^(-x) + _K1*e^x - x