New submission from Ned Batchelder <[email protected]>:
Looks like the optimizer is getting more aggressive. Line 2 (the constant
while) no longer even appears in the bytecode:
$ cat -n whiletrue.py
1 a = 1
2 while 1:
3 print(a)
4 b = 4
$ python3.7 -m dis < whiletrue.py
1 0 LOAD_CONST 0 (1)
2 STORE_NAME 0 (a)
2 4 SETUP_LOOP 12 (to 18)
3 >> 6 LOAD_NAME 1 (print)
8 LOAD_NAME 0 (a)
10 CALL_FUNCTION 1
12 POP_TOP
14 JUMP_ABSOLUTE 6
16 POP_BLOCK
4 >> 18 LOAD_CONST 1 (4)
20 STORE_NAME 2 (b)
22 LOAD_CONST 2 (None)
24 RETURN_VALUE
$ python3.8 -m dis < whiletrue.py
1 0 LOAD_CONST 0 (1)
2 STORE_NAME 0 (a)
3 >> 4 LOAD_NAME 1 (print)
6 LOAD_NAME 0 (a)
8 CALL_FUNCTION 1
10 POP_TOP
12 JUMP_ABSOLUTE 4
4 14 LOAD_CONST 1 (4)
16 STORE_NAME 2 (b)
18 LOAD_CONST 2 (None)
20 RETURN_VALUE
I understand why we want to make these optimizations. It's good for those
times when we run our programs. But there are other times: when we are
analyzing programs.
I'm begging you: please please please help me get
https://bugs.python.org/issue2506 implemented (a way to disable optimizations).
It is becoming more and more difficult to write tools that analyze Python
programs.
People are testing their libraries on Python 3.8-dev, and reporting problems
using coverage.py. I would like to support their efforts to test on the daily
Python builds. But it's difficult to keep coverage.py working under these
conditions.
Anything you can do would be really appreciated.
----------
components: Interpreter Core
messages: 327019
nosy: nedbat, serhiy.storchaka
priority: normal
severity: normal
status: open
title: Python3.8 optimizes away a "while" line
versions: Python 3.8
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<https://bugs.python.org/issue34888>
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