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Code object creation (const interning) can mutate tuples #121954

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@encukou

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@encukou

In #121863 (comment), 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

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