That's nice, thanks. Considering your last comment, some points

  * If the issue can't go into the error message, than the essence of the discussion here should go into the docs (in 0.5 to 1.5 sentences).
  * It'd be nice if it was clear from the error message that shelve or underlying modules check the extension in filename, i.e. do `anydbm.error: db type could not be determined by file extension '%s' in filename '%s'` rather than `anydbm.error: db type could not be determined`.