[New-bugs-announce] [issue42693] "if 0:" lines are traced; they didn't use to be

[Ned Batchelder]

New submission from Ned Batchelder <ned at nedbatchelder.com>:

(Using CPython commit c95f8bc270.)

This program has an "if 0:" line that becomes a NOP bytecode.  It didn't used to in Python 3.9

print(1)
if 0:               # line 2
    print(3)
print(4)

Using a simple trace program (https://github.com/nedbat/coveragepy/blob/master/lab/run_trace.py), it produces this output:

call <string> 1 @-1
    line <string> 1 @0
1
    line <string> 2 @8
    line <string> 4 @10
4
    return <string> 4 @20

Using Python3.9 gives this output:

call <string> 1 @-1
    line <string> 1 @0
1
    line <string> 4 @8
4
    return <string> 4 @18

Is this change intentional?

----------
messages: 383452
nosy: Mark.Shannon, nedbat
priority: normal
severity: normal
status: open
title: "if 0:" lines are traced; they didn't use to be
type: behavior
versions: Python 3.10

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue42693>
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