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Interestingly, co_filename is not used as part of the equivalence criteria, so code object equivalence can be fooled across multiple input files. Fortunately in this case, the false equivalence isn't relied on by the code generator.
 $ cat a.py
 def f():
 return 1
 $ cat b.py
 def f():
 return 1.0
 $ ./python.exe -q
 >>> import a, b
 >>> a.f.__code__ == b.f.__code__ # False equivalence
 True
 >>> a.f()
 1
 >>> b.f() # Generated code is correct
 1.0
Besides aliasing int/float/decimal/fraction/complex/bool, codeobj.__eq__() can also alias str/unicode on Python 2.7. Likewise, 0.0 and -0.0 can be conflated. NaNs don't seem to be a problem.
I think we should focus on fixing the spec for code object equivalents. Perhaps the test can be simplified to use (co_firstlineno, co_firstrowno, co_filename).