On Tue, 10 Apr 2018 18:49:36 +0300 Serhiy Storchaka <storch...@gmail.com> wrote: > > 1. More stable file signature. Currently the magic number is changed in > every feature release. Only the third and the forth bytes are stable > (b'\r\n'), the first bytes are changed non-predicable. The 'py' launcher > and third-party software like the 'file' command should support the list > of magic numbers for all existing Python releases, and they can't detect > pyc file for future versions. There is also a chance the pyc file > signature will match the signature of other file type by accident. It > would be better if the first 4 bytes of pyc files be same for all Python > versions (or at least for all Python versions with the same major number).
+1. > 2. Include the Python version. Currently the 'py' launcher needs to > support the table that maps magic numbers to Python version. It can > recognize only Python versions released before building the launcher. If > the two major numbers of Python version be included in the version, it > would not need such table. +1. > 3. The number of compatible subversion. Currently the interpreter > supports only a single magic number. If the updated version of the > compiler produces more optimal or more correct but compatible bytecode > (like ), there is no way to say that the new bytecode is preferable, but > the old bytecode can be used too. Changing the magic number causes > invalidating all pyc files compiled by the old compiler (see  for the > example of problems caused by this). The header could contain two magic > numbers: the major magic number should be bumped for incompatible > changes, the minor magic number should be reset to 0 when the major > magic number is bumped, and should be bumped when the compiler become > producing different but compatible bytecode. -1. This is a risky move (and costly, in maintenance terms). It's easy to overlook subtle differencies that may translate into incompatibilities in some production uses. The rule « one Python feature release == one bytecode version » is easy to remember and understand, and is generally very well accepted. Regards Antoine. _______________________________________________ Python-ideas mailing list Pythonfirstname.lastname@example.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/