foo.py

__requires__ = ['pymongo']
__index_url__ = 'https://m.devpi.net/jaraco/dev'

import datetime
import decimal

import pymongo
import bson.codec_options as opts
from bson import decimal128


class DecimalCodec(opts.TypeCodecBase):
    python_type = decimal.Decimal
    bson_type = decimal128.Decimal128
    transform_python = decimal128.Decimal128

    def transform_bson(self, value):
        return value.to_decimal()


url = 'mongodb://localhost/test'
tz_aware = opts.CodecOptions(tz_aware=True, tzinfo=datetime.timezone.utc)
db = pymongo.MongoClient(url).get_database(codec_options=tz_aware)
codec = DecimalCodec()
registry = opts.TypeRegistry(codec)

doc = dict(now=datetime.datetime.now(), val=decimal128.Decimal128('1.0'))
db.coll.drop()
db.coll.insert_one(doc)

# query db.coll using the type registry
print(list(db.coll.with_options(
    codec_options=db.coll.codec_options.with_options(type_registry=registry),
).find({})))
db.coll.drop()