python bytecode compatibility

Question

To what extent is python bytecode compatible between releases. I\'m not talking about python2.x to python3.x but say... Python33 to python34?

I am not after it for \

Answer 1

Python makes no guarantee about bytecode compatibility between versions. Don't rely on it.

In fact, a pyc file starts with a magic number that changes every time the marshalling code does, and python checks this number for compatibility. Since this code changes pretty much every version, so does the magic number. See Ned Batchelder's blog entry for details.

There are better ways of ensuring your files haven't been tampered with: checksums, for example.