Check if active object has a modifier How can I check if the Active Object has a specific modifier so that when I run my code, it doesn't add the modifier again to the object? It should add the modifier only to the object which does not use that modifier.
Check object for modifiers

import bpy

obj = bpy.context.object

if not obj.modifiers:
    print ("no modifiers")
else:
    print ("object has modifier(s)")


Check object for specific modifiers

import bpy

obj = bpy.context.object

for modifier in obj.modifiers:
    if modifier.type == "SUBSURF":
        print ("subsurf")


For all types see: http://www.blender.org/api/blender_python_api_current/bpy.types.Modifier.html?highlight=subsurf#bpy.types.Modifier.type



In your case I'd recommend using a list comprehension which returns True or False:

print(0 &lt; len([m for m in bpy.context.object.modifiers if m.type == "SUBSURF"]))


or Python's any() plus the list comprehension.

print(any([m for m in bpy.context.object.modifiers if m.type == "SUBSURF"]))




Adding the Modifier if it isn't present

import bpy

obj = bpy.context.active_object
subsurf = obj.modifiers.new(name='MySubSurf', type='SUBSURF')
subsurf.levels = 2
subsurf.render_levels = 3