The GDB and LLDB pretty-printers (in mongo_printers.py and lldb_printers.py) were updated to call bson.decode() in SERVER-43055. The bson.decode() convenience method was introduced in PyMongo 3.9.0, but in core.req we require only "pymongo >= 3.0, != 3.6.0". If we depend on the bson.decode() method we must require "pymongo >= 3.9.0".

Currently, if you have PyMongo before 3.9.0 and try to print a BSONObj in the GDB console, you see something like "AttributeError: module 'bson' has no attribute 'decode'".