There was a subtle big in save_newobj(): it used self.save_global(t)
on the type instead of self.save(t). This defeated the purpose of NEWOBJ, because it didn't generate a BINGET opcode when t was already memoized; but moreover, it would generate multiple BINPUT opcodes for the same type! pickletools.dis() doesn't like this. How I found this? I was playing with picklesize.py in the datetime sandbox, and noticed that protocol 2 pickles for multiple objects were in fact larger than protocol 1 pickles! That was suspicious, so I decided to disassemble one of the pickles. This really needs a unit test, but I'm exhausted. I'll be late for work as it is. :-(
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@ -233,6 +233,7 @@ class Pickler:
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# growable) array, indexed by memo key.
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if self.fast:
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return
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assert id(obj) not in self.memo
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memo_len = len(self.memo)
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self.write(self.put(memo_len))
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self.memo[id(obj)] = memo_len, obj
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@ -386,7 +387,7 @@ class Pickler:
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save = self.save
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write = self.write
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self.save_global(t)
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self.save(t)
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save(args)
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write(NEWOBJ)
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self.memoize(obj)
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