In Lib/encodings/__init__.py, search_function() looks up an encoding by name.  It loads the encoding by importing the corresponding module in the encodings package.  If there's an ImportError while importing that module then the encoding gets silently ignored.  I noticed this while working on issue #16384.

While I don't have any direct interest in the matter, I expect that it would be more useful to users if we issued a warning or some other printed message when an encoding is ignored.