For example in tutorial: https://api.mongodb.com/python/3.7.1/tutorial.html#counting

 >>> posts.count()
3

or just of those documents that match a specific query:

>>> posts.find(

Unknown macro: {"author"}

).count()

2

Also in API documentation: https://api.mongodb.com/python/3.7.1/api/pymongo/collection.html#pymongo.collection.Collection.insert_one