Blender API - Use data-block name as if condition

Question

I'm trying to make a python script that searches for an existing camera data-block in the scene and creates it if not found.

I've gone with a rather simple code:

for dcam in bpy.data.cameras:
     if dcam.name == "PERSP.Camera":
         break
     else:
         bpy.data.cameras.new("PERSP.Camera")

However, what I've written will keep creating increments of "PERSP.Camera" despite the condition checking if there isn't already a camera with this name.

I'm relatively new to python. Am I missing something about data-blocks where their names cannot be accessed if they're within a loop/not linked to an object in the scene?

Answer 1

Your code is only creating the data block for the camera. You also need to create a camera object and link that to the a collection in your scene. Also, your for loop creates a new camera every time it finds a camera data block NOT named "PERSP.Camera"

You want something more like:

import bpy

col = bpy.context.collection # get active collection
test = False

for dcam in bpy.data.cameras:
    if dcam.name == "PERSP.Camera_Data":
        test = True # remember one of the camera data blocks is named PERSP.Camera_Data

if not test: # camera data block not found
    new_cam_data = bpy.data.cameras.new("PERSP.Camera_Data") # create the camera data block
    new_cam_obj = bpy.data.objects.new("PERSP.Camera", new_cam_data) # create the camera object
    col.objects.link(new_cam_obj) # link the camera object to a the active collection

Answer 2

I think you're overcomplicating things with your loop. Try something like :

import bpy

cam_name = "PERSP.Camera"
cam = bpy.data.cameras.get(cam_name)
if cam is None:
    cam = bpy.data.cameras.new(cam_name)

bpy.data.cameras acts like a dictionary. You can use get to test if an element is inside it. If not, it will return None.

You can also use the slightly more pythonic but weirder

cam = bpy.data.cameras.get(cam_name) or bpy.data.cameras.new(cam_name)