New submission from Ned Batchelder <n...@nedbatchelder.com>:
Python 3.11.0a3 changed how f_lasti behaves when calling a function in some
situations.
This example shows returning a lambda from a function. If the lambda is
returned in a loop, then frame.f_lasti is 0 when it is called. If the lambda
is not in a loop, then f_lasti is -1, as is usual when calling a function.
This behavior first appeared in 3.11.0a3.
---< showit.py >--------------------------------------------------
import linecache, sys
def trace(frame, event, arg):
# The weird globals here is to avoid a NameError on shutdown...
if frame.f_code.co_filename == globals().get("__file__"):
if event != "line":
lineno = frame.f_lineno
lasti = f"lasti {frame.f_lasti}" if event == "call" else ""
line = linecache.getline(__file__, lineno).rstrip()
print("{} {} {:10}: {}".format(event[:4], lineno, lasti, line))
return trace
print(sys.version)
sys.settrace(trace)
def run1():
for i in range(1):
return lambda: i
def run2():
return lambda: 99
f = run1()
print(f())
f = run2()
print(f())
------------------------------------------------------------------
Here are 3.10, 3.11.0a2, 3.11.0a3, and the tip of 3.11. The changing line is
marked with <<<<<:
$ python3.10 showit.py
3.10.1 (main, Dec 14 2021, 08:30:13) [Clang 12.0.0 (clang-1200.0.32.29)]
call 16 lasti -1 : def run1():
retu 18 : return lambda: i
call 18 lasti -1 : return lambda: i <<<<<
retu 18 : return lambda: i
0
call 20 lasti -1 : def run2():
retu 21 : return lambda: 99
call 21 lasti -1 : return lambda: 99
retu 21 : return lambda: 99
99
$ /usr/local/pyenv/pyenv/versions/3.11.0a2/bin/python3.11 showit.py
3.11.0a2 (main, Nov 6 2021, 07:16:30) [Clang 12.0.0 (clang-1200.0.32.29)]
call 16 lasti -1 : def run1():
retu 18 : return lambda: i
call 18 lasti -1 : return lambda: i <<<<<
retu 18 : return lambda: i
0
call 20 lasti -1 : def run2():
retu 21 : return lambda: 99
call 21 lasti -1 : return lambda: 99
retu 21 : return lambda: 99
99
$ /usr/local/pyenv/pyenv/versions/3.11.0a3/bin/python3.11 showit.py
3.11.0a3 (main, Dec 9 2021, 12:22:18) [Clang 12.0.0 (clang-1200.0.32.29)]
call 16 lasti -1 : def run1():
retu 18 : return lambda: i
call 18 lasti 0 : return lambda: i <<<<<
retu 18 : return lambda: i
0
call 20 lasti -1 : def run2():
retu 21 : return lambda: 99
call 21 lasti -1 : return lambda: 99
retu 21 : return lambda: 99
99
$ /usr/local/cpython/bin/python3 showit.py
3.11.0a3+ (heads/main:a82baed0e9, Jan 2 2022, 08:12:01) [Clang 12.0.0
(clang-1200.0.32.29)]
call 16 lasti -1 : def run1():
retu 18 : return lambda: i
call 18 lasti 0 : return lambda: i <<<<<
retu 18 : return lambda: i
0
call 20 lasti -1 : def run2():
retu 21 : return lambda: 99
call 21 lasti -1 : return lambda: 99
retu 21 : return lambda: 99
99
----------
keywords: 3.11regression
messages: 409496
nosy: Mark.Shannon, nedbat
priority: normal
severity: normal
status: open
title: f_lasti behaves differently for lambdas returned from loops
versions: Python 3.11
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue46225>
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