[Python-Dev] The purpose of SETUP_LOOP, BREAK_LOOP, CONTINUE_LOOP (original) (raw)

Antoine Pitrou solipsis at pitrou.net
Sat Mar 12 11:59:01 CET 2011

Hello,

Am I missing something? Does SETUPLOOP serve any other purpose?

Not to my knowledge.

Similarly, it looks like BREAKLOOP and CONTINUELOOP are just jumps that respect try/finally blocks (i.e. jumping out of try executes finally). Is there more semantics to them than this?

There are also "with" blocks :-) (which use separate opcodes, although they are similar in principle to try/finally blocks)

1) If not in try/finally, simply generate a direct jump outside of the loop (break) or to the start of the loop (continue).

Right.

2) If in try/finally, generate a new instruction JUMPFROMTRY which replaces both BREAKLOOP and CONTINUELOOP. It behaves the same way as CONTINUELOOP but without restriction to only jump backwards (could reuse CONTINUELOOP, but the name would be misleading).

There may be complications with nested try/finally blocks. You either need to generate separate bytecode for when the "finally" clause is entered following a given continue/break (so as to hardcode the jump offset at the end of the clause), or save the jump offsets somewhere on a stack for each finally clause to pop, IMO.

(the current code does the latter with various complications, see WITH_CLEANUP for some aspects of the fun)

Regards

Antoine.

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