• name: lonepycfiles
  • description: Import pyc files with no matching py file
  • command-line: –objspace-lonepycfiles
  • command-line for negation: –no-objspace-lonepycfiles
  • option type: boolean option
  • default: False

If turned on, PyPy accepts to import a module x if it finds a file x.pyc even if there is no file x.py.

This is the way that CPython behaves, but it is disabled by default for PyPy because it is a common cause of issues: most typically, the x.py file is removed (manually or by a version control system) but the x module remains accidentally importable because the x.pyc file stays around.

The usual reason for wanting this feature is to distribute non-open-source Python programs by distributing pyc files only, but this use case is not practical for PyPy at the moment because multiple versions of PyPy compiled with various optimizations might be unable to load each other’s pyc files.