def register_previewer(self, name, previewer):
if name in self.previewers:<EOL><INDENT>assert name not in self.previewers,"<STR_LIT>"<EOL><DEDENT>self.previewers[name] = previewer<EOL>if hasattr(previewer, '<STR_LIT>'):<EOL><INDENT>self._previewable_extensions |= set(<EOL>previewer.previewable_extensions)<EOL><DEDENT>
Register a previewer in the system.