Just on the off chance that you are trying to just make gridlines, here are some examples from the documentation:

```
sage: p = polar_plot(2 + 2*cos(x), 0, 2*pi, color=hue(0.3))
sage: p.show(gridlines=True,
... hgridlinesstyle=dict(color="orange", linewidth=1.0),
... vgridlinesstyle=dict(color="blue", linestyle=":"))
Change the style of each grid line individually.
sage: x, y = var('x, y')
sage: p = implicit_plot((y^2-x^2)*(x-1)*(2*x-3)-4*(x^2+y^2-2*x)^2,
... (x,-2,2), (y,-2,2), plot_points=1000)
sage: p.show(gridlines=(
... [
... (1,{"color":"red","linestyle":":"}),
... (0,{"color":"blue","linestyle":"--"})
... ],
... [
... (-1,{"color":"red","linestyle":":"}),
... (0,{"color":"blue","linestyle":"--"}),
... (1,{"color":"red","linestyle":":"}),
... ]
... ),
... gridlinesstyle=dict(marker='x',color="black"))
```

There are pretty finely-grained options available.

By the way, you can do `for i in [-3..2]` if you are looking for a more intuitive way to write that range.