Have you tried it? You are right in general, but even if you don't write anything in Python, CPython runtime constantly writes to heap, so everything is copied.

Have you tried it? You are right in general, but even if you don't write anything in Python, CPython runtime constantly writes to heap, so everything is copied. You need specific support from CPython runtime to exploit copy-on-write. This is documented: https://docs.python.org/3/library/gc.html#gc.freeze https://docs.python.org/3/library/gc.html#gc.freeze For details, see "Copy-on-write friendly Python garbage collection" by Instagram Engineering: https://instagram-engineering.com/copy-on-write-friendly-python-garbage-collection-ad6ed5233ddf https://instagram-engineering.com/copy-on-write-friendly-pyt...