Blender Python API: Gets collections by creating them or getting them by name.

get_blender_collection.py

import bpy

def get_collection(collection_name: str) -> bpy.types.Collection:
    return bpy.data.collections.get(collection_name) or bpy.data.collections.new(collection_name)

def get_collections(collection_names: list) -> list:
    return [get_collection(collection_name) for collection_name in collection_names]

if __name__ == __main__:
    get_collection("TEST_COLLECTION")
    get_collections(["TEST_COLLECTION", "COL1", "COL2"])