A simple Python example on how to serialise/deserialise MongoDB ObjectID() using PyYAML.

ObjectID_YAML.py

import yaml
from pymongo import MongoClient
from bson import objectid

def objectid_representer(dumper, data):
    return dumper.represent_scalar("!bson.objectid.ObjectId", str(data))

def objectid_constructor(loader, data):
    return objectid.ObjectId(loader.construct_scalar(data))

def sample_mongodb_doc():
    client = MongoClient()
    return client.test.yaml.find_one()

def main():
    # Fetch a single document from MongoDB, which contains {_id:ObjectID(...)}.
    doc = sample_mongodb_doc()
    print(doc)

    # Serialise dict containing ObjectID into yaml file. 
    yamlfile = open('data.yaml', 'wb')
    yaml.SafeDumper.add_representer(objectid.ObjectId, objectid_representer)
    yaml.safe_dump(doc, yamlfile, default_flow_style=False)
    yamlfile.close()

    # Deserialise yaml file back into a dict. 
    yaml.add_constructor('!bson.objectid.ObjectId', objectid_constructor)
    loaded = yaml.load(open('data.yaml', 'r'))
    print(loaded)


if __name__ == "__main__":
    main()