Message406283
This also tripped me up recently. More broadly, I assumed that handlers downstream of the QueueHandler/QueueListener would get complete log records. Having looked at it, I can see they need to be pickled, and that means stripping some information. But like Mikael, I found the current behaviour a bit confusing.
The solution I am using is to override logging.Formatter.format and QueueHandler.Prepare like so:
class _OptionalExcFormatter(logging.Formatter):
def format(self, record, with_exc=True, with_stack=True):
"""
Format the specified record as text.
Same as superclass except it only adds the exc_info and stack_info if
the corresponding arguments are True.
"""
record.message = record.getMessage()
if self.usesTime():
record.asctime = self.formatTime(record, self.datefmt)
s = self.formatMessage(record)
if record.exc_info and with_exc:
# Cache the traceback text to avoid converting it multiple times
# (it's constant anyway)
if not record.exc_text:
record.exc_text = self.formatException(record.exc_info)
if record.exc_text and with_exc:
if s[-1:] != "\n":
s = s + "\n"
s = s + record.exc_text
if record.stack_info and with_stack:
if s[-1:] != "\n":
s = s + "\n"
s = s + self.formatStack(record.stack_info)
return s
class _QueueHandlerExc(QueueHandler):
def prepare(self, record):
# bpo-35726: make copy of record to avoid affecting other handlers in the chain.
record = copy.copy(record)
# Get a formatter. It must support the with_exc and with_stack args to f.format
if self.formatter is None:
f = _OptionalExcFormatter()
else:
f = self.formatter
# Merge args into message and strip them as they may not be pickleable
msg = f.format(record, with_exc=False, with_stack=False)
record.message = msg
record.msg = msg
record.args = None
# Convert exc_info into exc_text and strip it as it may not be pickleable
if record.exc_info is not None:
record.exc_text = f.formatException(record.exc_info)
record.exc_info = None
return record
Pros:
- The record feels "less mangled"
- It does not require another formatter to have already populated exc_text, and allows the use of a specific formatter to do so.
- Having the message and exc_text separate seems logical, and allows downstream handlers/formatters to treat them differently.
- logging.Formatter can get the changes above in a back-compatible way
Cons:
- exc_text now contains the stack trace as well as the usual exc_info, which is a little odd, but it still seems to be a better place for it than the message.
- If QueueHandler gets the changes above, it will break code where QueueHandler is used with a custom Formatter which overrides Formatter.format. This is probably not OK.
I think the changes to logging.Formatter might also be useful elsewhere, as it would enable you to do:
class _NoStackFormatter(logging.Formatter):
def format(self, record):
return super().format(record, with_exc=True, with_stack=False)
to have a formatter which omits stack traces. |
|
Date |
User |
Action |
Args |
2021-11-13 15:51:11 | Jack_B | set | recipients:
+ Jack_B, vinay.sajip, zach.ware, Miksus |
2021-11-13 15:51:11 | Jack_B | set | messageid: <1636818671.21.0.782364096479.issue44924@roundup.psfhosted.org> |
2021-11-13 15:51:11 | Jack_B | link | issue44924 messages |
2021-11-13 15:51:10 | Jack_B | create | |
|