SDS on, off, only key

Coding Beginning Blender Code and Development
1

Hi, I just started to learn programming, and immediately ran into a problem. Help solve the problem.
Sorry for the english, I use Google translator

import bpy

sel = bpy.context.selected_objects
mod = bpy.types.ObjectModifiers
obj = bpy.context.object


for i in sel:
    for j in mod:
        if modifier.type != 'SUBSURF':
            bpy.ops.object.modifier_add(type='SUBSURF')
            bpy.context.object.modifiers['SUBSURF'].levels = 2
        else: modifier.type == 'SUBSURF'
            obj.modifiers.clear()
2

and this does not work

import bpy

sel = bpy.context.selected_objects


bool var = true


for i in sel:
    for j in i.modifiers:
        if j.type != 'SUBSURF':
            var = true
            
if var == true:
    sel = bpy.ops.object.modifier_add(type='SUBSURF')
elif var == false:
    for i in sel:
        for j in i.modifiers:
            i.modifiers.remove(j)
3


Thank you all for your help, the script started

import bpy

sel = bpy.context.selected_objects

obj = bpy.context.object

var = 3

for i in sel:
for j in i.modifiers:
if (j.type == ‘SUBSURF’):
var = 0

#print(var)
if var == 0:
for i in sel:
for j in i.modifiers:
if (j.type == ‘SUBSURF’):
i.modifiers.remove(j)

elif var == 3:
obj = bpy.context.active_object
subsurf = obj.modifiers.new(name=‘SUBSURF’, type=‘SUBSURF’)
subsurf.levels = 2
subsurf.render_levels = 2
subsurf.show_on_cage = True