I copy/paste:
mylayers = [False] * 20

then hit return

then I copy/paste:
mylayers[0] = True

then I hit return

then I copy/paste:
add_cube = bpy.ops.mesh.primitive_cube_add

then hit return

then I copy/paste:
for index in range(0, 5):
... add_cube(location=(index * 3, 0, 0), layers=mylayers)

then hit return

and this shows up in red:

File "<blender_console>", line 2
  ...     add_cube(location=(index * 3, 0, 0), layers=mylayers)
    ^

IndentationError: expected an indented block