Code object creation (const interning) can mutate tuples

In https://github.com/python/cpython/issues/121863#issuecomment-2232849007, Mark suspected something is off in const interning for code objects. Indeed, there is. For example:

# a bit of setup
import sys
interned = sys.intern("foobar")
def f():
    var = "foobar"

# my_tuple = (None, 'foobar'), but with an un-interned string
my_tuple = (None, str(b'foobar', 'ascii'))  

print(id(my_tuple), id(my_tuple[1]))

# pass my_tuple as an input argument for a new code object
f.__code__.replace(co_consts=my_tuple)

# there's now a different object in the tuple!
print(id(my_tuple), id(my_tuple[1]))

I'm working on a change to:

• create new tuples instead of mutating old ones
• intern more strings before passing them to PyCode constructors, so that we usually don't need to create new tuples

Linked PRs

• gh-122180