New submission from Andrius Laukavičius <anlauka...@gmail.com>:
It looks like logging library uses always first assigned stderr object and
won't change it even if it was reset.
capture_output function redirects stdout and stderr to io.StringIO object,
saves what was captured in string and returns it. And then context manager
resets back stdout and stderr where it should be originally. Though it seems
logging library ignores that.
Here is the code I encountered issue with:
import io
import sys
import contextlib
from typing import Optional
import logging
def capture_output(
target: object,
args: Optional[tuple] = None,
kwargs: Optional[dict] = None) -> str:
"""Redirect stdout and stderr into string buffer and capture it.
target object is executed with optional args, kwargs and all stdout/
stderr that is captured, returned in string form.
Args:
target: object to execute, usually a function.
args: target positional arguments (default: {None})
kwargs: target keyword arguments (default: {None})
"""
if not args:
args = ()
if not kwargs:
kwargs = {}
with io.StringIO() as sio:
with contextlib.redirect_stdout(sio), contextlib.redirect_stderr(sio):
target(*args, **kwargs)
output = sio.getvalue()
print(output)
def dummy():
print('dummy test')
logging.warning('dummy test')
def dummy2():
print('dummy2 test')
capture_output(dummy) # works
capture_output(dummy) # won't work anymore.
capture_output(dummy2) # works
capture_output(dummy2) # works
Here is what I get running this code:
dummy test
WARNING:root:dummy test
dummy test
--- Logging error ---
Traceback (most recent call last):
File "/usr/lib/python3.5/logging/__init__.py", line 982, in emit
stream.write(msg)
ValueError: I/O operation on closed file
Call stack:
File "tt.py", line 43, in <module>
capture_output(dummy) # won't work anymore.
File "tt.py", line 28, in capture_output
target(*args, **kwargs)
File "tt.py", line 36, in dummy
logging.warning('dummy test')
Message: 'dummy test'
Arguments: ()
dummy2 test
dummy2 test
P.S. here is original question I asked on stack overflow:
https://stackoverflow.com/questions/54999650/python3-redirected-stderr-not-reset-properly.
I got suggestion to report it as a bug.
----------
components: Library (Lib)
messages: 337178
nosy: Andrius Laukavičius
priority: normal
severity: normal
status: open
title: Redirected stderr not reset properly when using logging
type: behavior
versions: Python 3.5
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue36193>
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