[New-bugs-announce] [issue34705] Python 3.8 changes how returns through finally clauses are traced

[Ned Batchelder]

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

When a return statement also executes a finally clause, the sequence of lines reported to the trace function is different in 3.8 than it has been before 3.8:

$ cat finally_trace.py
def return_from_finally():
    try:
        print("returning")
        return 17
    finally:
        print("finally")

def trace(frame, event, arg):
    print(frame.f_lineno, event)
    return trace

import sys
sys.settrace(trace)
return_from_finally()

$ python3.7 finally_trace.py
1 call
2 line
3 line
returning
4 line
6 line
finally
6 return

$ python3.8 finally_trace.py
1 call
2 line
3 line
returning
4 line
6 line
finally
4 line
4 return


Is this intentional? Is it a bug? Will it change back before 3.8 is shipped?

----------
components: Interpreter Core
messages: 325484
nosy: nedbat
priority: normal
severity: normal
status: open
title: Python 3.8 changes how returns through finally clauses are traced
type: behavior
versions: Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue34705>
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