From my understanding on how this tag is used, this wouldn't be a
In issue 25483 I'm adding an opcode to make f-string formatting more robust and faster. As part of that, I'm bumping the .pyc magic number. While doing that, I notice Lib/importlib/_bootstrap_external.h includes this comment: # Starting with the adoption of PEP 3147 in Python 3.2, every bump in magic # number also includes a new "magic tag", i.e. a human readable string used # to represent the magic number in __pycache__ directories. When you change # the magic number, you must also set a new unique magic tag. Generally this # can be named after the Python major version of the magic number bump, but # it can really be anything, as long as it's different than anything else # that's come before. The tags are included in the following table, starting # with Python 3.2a0. The "following table" is a comment, that contains a few references to the tag "cpython-<version>", specifically cpython-32. It doesn't seem that the tag is routinely updated in the comment. sys.implementation.cache_tag returns 'cpython-36', and is in fact implemented as 'cpython-{PY_MAJOR_VERSION}{PY_MINOR_VERSION}'. Do I need to do anything else? Unlike what the comment in _boostrap_external.py suggests, this "magic tag" will not change every time a bytecode is added, but only on every minor release. Which implies that if we have a micro release that adds an opcode, we'll in fact break the promise in the comment. problem (because the magic number in the file also changes). But I want to make sure I'm not misunderstanding something. I think the comment above is probably just misleading. Eric.