## 6.1.2 ``Compiled'' Python files

As an important speed-up of the start-up time for short programs that use a lot of standard modules, if a file called ``spam.pyc`' exists in the directory where ``spam.py`' is found, this is assumed to contain an already-``compiled'' version of the module `spam`. The modification time of the version of ``spam.py`' used to create ``spam.pyc`' is recorded in ``spam.pyc`', and the file is ignored if these don't match.

Normally, you don't need to do anything to create the ``spam.pyc`' file. Whenever ``spam.py`' is successfully compiled, an attempt is made to write the compiled version to ``spam.pyc`'. It is not an error if this attempt fails; if for any reason the file is not written completely, the resulting ``spam.pyc`' file will be recognized as invalid and thus ignored later. The contents of the ``spam.pyc`' file is platform independent, so a Python module directory can be shared by machines of different architectures. (Tip for experts: the module `compileall` creates file.pyc files for all modules.)

XXX Should optimization with -O be covered here?