How to get minimum value in pyMongo
You can reverse the sort direction to get the minimum instead of the maximum value:

 # Sort by myfield (ascending value) and return first document
 collection.find_one(sort=[("myfield", 1)])["myfield"]


This example assumes that:


myfield is a numeric value (so the sort order makes sense to determine a minimum or maximum)
myfield exists in the matching document returned (otherwise Python will report a KeyError when trying to reference a non-existent field).
all documents in the collection have a myfield value (documents that have do not have a myfield value will sorted before the minimum numeric values)


To ensure your sort is based on documents that actually have a myfield value you can add $exists to the query criteria:

 collection.find_one({"myfield": {"$exists": True}}, sort=[("myfield", 1)])["myfield"]


For more information on sorting see:


Use Indexes to Sort Query Results
What is the compare order for BSON types?