mongo_concat_sort.py

from pprint import pprint

import pymongo


client = pymongo.MongoClient()
db = client.test_database

if not db.users.count():
    db.users.insert({
        'first_name': 'John',
        'last_name': 'Smith'
    })
    db.users.insert({
        'first_name': 'Tom',
        'last_name': 'Taylor'
    })

result = client.test_database.users.aggregate([
    {"$project": {
        "full_name": {"$concat": ["$first_name", " ", "$last_name"]}
    }},
    {"$sort": {"full_name": 1}}
])

pprint(result)