from sympy import *
var('a:z C1 C2');
y = Function('y')
de = diff(y(t),t,t) + y(t)
f = Lambda((t,C1,C2) , dsolve(de,y(t)).args[1])
p = plot(f(t,1,0),f(t,0,1),(t,0,4*pi),ylim=(-1.5,1.5),
   show=False,title='$'+latex(de)+'=0$')
p[0].line_color = 'DarkGreen'
p[1].line_color = 'DarkRed'
p.show()