[Python-Dev] Unexpected bytecode difference

[Victor Stinner]

Python bytecode format changed deeply in Python 3.6. It now uses
regular units of 2 bytes, instead of 1 or 3 bytes depending if the
instruction has an argument.

See for example https://bugs.python.org/issue26647 "wordcode".

But CALL_FUNCTION bytecode also evolved.

Victor

2018-01-20 0:46 GMT+01:00 Alexander Belopolsky <alexander.belopolsky at gmail.com>:
> I have encountered the following difference between Python 3 and 2:
>
> (py3)
>>>> compile('xxx', '<>', 'eval').co_code
> b'e\x00S\x00'
>
> (py2)
>>>> compile('xxx', '<>', 'eval').co_code
> 'e\x00\x00S'
>
> Note that 'S' (the code for RETURN_VALUE) and a zero byte are swapped
> in Python 2 compared to Python 3.  Is this change documented
> somewhere?
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