From https://stackoverflow.com/questions/5499897/converting-selenium-py-to-python-3-by-2to3, 2to3 prints the following messages when run:

===============
RefactoringTool: Skipping implicit fixer: buffer
RefactoringTool: Skipping implicit fixer: idioms
RefactoringTool: Skipping implicit fixer: set_literal
RefactoringTool: Skipping implicit fixer: ws_comma
===============

That message is rather misleading - those four are the *optional* fixers that are only run when selected explicitly. Unlike the other fixers, they're essentially the *opposite* of implicit :)

Given that limiting the fixes to a specific subset (e.g. "-f dict") silences all such messages, and explicitly excluding an actual implicit fixer (e.g. "-x dict") doesn't generate a warning, I suggest the simplest fix is to just change the message to instead say "Skipping optional fixer".