问题
I use logging facility for python 2.7.3. Documentation for this Python version say:
the logging package pre-dates newer formatting options such as str.format() and string.Template. These newer formatting options are supported...
I like \'new\' format with curly braces. So i\'m trying to do something like:
log = logging.getLogger(\"some.logger\")
log.debug(\"format this message {0}\", 1)
And get error:
TypeError: not all arguments converted during string formatting
What I miss here?
P.S. I don\'t want to use
log.debug(\"format this message {0}\".format(1))
because in this case the message is always being formatted regardless of logger level.
回答1:
EDIT: take a look at the StyleAdapter approach in @Dunes' answer unlike this answer; it allows to use alternative formatting styles without the boilerplate while calling logger's methods (debug(), info(), error(), etc).
From the docs — Use of alternative formatting styles:
Logging calls (logger.debug(), logger.info() etc.) only take positional parameters for the actual logging message itself, with keyword parameters used only for determining options for how to handle the actual logging call (e.g. the exc_info keyword parameter to indicate that traceback information should be logged, or the extra keyword parameter to indicate additional contextual information to be added to the log). So you cannot directly make logging calls using str.format() or string.Template syntax, because internally the logging package uses %-formatting to merge the format string and the variable arguments. There would no changing this while preserving backward compatibility, since all logging calls which are out there in existing code will be using %-format strings.
And:
There is, however, a way that you can use {}- and $- formatting to construct your individual log messages. Recall that for a message you can use an arbitrary object as a message format string, and that the logging package will call str() on that object to get the actual format string.
Copy-paste this to wherever module:
class BraceMessage(object):
def __init__(self, fmt, *args, **kwargs):
self.fmt = fmt
self.args = args
self.kwargs = kwargs
def __str__(self):
return self.fmt.format(*self.args, **self.kwargs)
Then:
from wherever import BraceMessage as __
log.debug(__('Message with {0} {name}', 2, name='placeholders'))
Note: actual formatting is delayed until it is necessary e.g., if DEBUG messages are not logged then the formatting is not performed at all.
回答2:
Here is another option that does not have the keyword problems mentioned in Dunes' answer. It can only handle positional ({0}) arguments and not keyword ({foo}) arguments. It also does not require two calls to format (using the underscore). It does have the ick-factor of subclassing str:
class BraceString(str):
def __mod__(self, other):
return self.format(*other)
def __str__(self):
return self
class StyleAdapter(logging.LoggerAdapter):
def __init__(self, logger, extra=None):
super(StyleAdapter, self).__init__(logger, extra)
def process(self, msg, kwargs):
if kwargs.pop('style', "%") == "{": # optional
msg = BraceString(msg)
return msg, kwargs
You use it like this:
logger = StyleAdapter(logging.getLogger(__name__))
logger.info("knights:{0}", "ni", style="{")
logger.info("knights:{}", "shrubbery", style="{")
Of course, you can remove the check noted with # optional to force all messages through the adapter to use new-style formatting.
Note for anyone reading this answer years later: Starting with Python 3.2, you can use the style parameter with Formatter objects:
Logging (as of 3.2) provides improved support for these two additional formatting styles. The Formatter class been enhanced to take an additional, optional keyword parameter named
style. This defaults to'%', but other possible values are'{'and'$', which correspond to the other two formatting styles. Backwards compatibility is maintained by default (as you would expect), but by explicitly specifying a style parameter, you get the ability to specify format strings which work with str.format() or string.Template.
The docs provide the example
logging.Formatter('{asctime} {name} {levelname:8s} {message}', style='{')
Note that in this case you still can't call the logger with the new format. I.e., the following still won't work:
logger.info("knights:{say}", say="ni") # Doesn't work!
logger.info("knights:{0}", "ni") # Doesn't work either
回答3:
This was my solution to the problem when I found logging only uses printf style formatting. It allows logging calls to remain the same -- no special syntax such as log.info(__("val is {}", "x")). The change required to code is to wrap the logger in a StyleAdapter.
from inspect import getargspec
class BraceMessage(object):
def __init__(self, fmt, args, kwargs):
self.fmt = fmt
self.args = args
self.kwargs = kwargs
def __str__(self):
return str(self.fmt).format(*self.args, **self.kwargs)
class StyleAdapter(logging.LoggerAdapter):
def __init__(self, logger):
self.logger = logger
def log(self, level, msg, *args, **kwargs):
if self.isEnabledFor(level):
msg, log_kwargs = self.process(msg, kwargs)
self.logger._log(level, BraceMessage(msg, args, kwargs), (),
**log_kwargs)
def process(self, msg, kwargs):
return msg, {key: kwargs[key]
for key in getargspec(self.logger._log).args[1:] if key in kwargs}
Usage is:
log = StyleAdapter(logging.getLogger(__name__))
log.info("a log message using {type} substiution", type="brace")
It's worth noting that this implementation has problems if key words used for brace substitution include level, msg, args, exc_info, extra or stack_info. These are argument names used by the log method of Logger. If you need to one of these names then modify process to exclude these names or just remove log_kwargs from the _log call. On a further note, this implementation also silently ignores misspelled keywords meant for the Logger (eg. ectra).
回答4:
The easier solution would be to use the excellent logbook module
import logbook
import sys
logbook.StreamHandler(sys.stdout).push_application()
logbook.debug('Format this message {k}', k=1)
Or the more complete:
>>> import logbook
>>> import sys
>>> logbook.StreamHandler(sys.stdout).push_application()
>>> log = logbook.Logger('MyLog')
>>> log.debug('Format this message {k}', k=1)
[2017-05-06 21:46:52.578329] DEBUG: MyLog: Format this message 1
回答5:
As other answers mention, the brace-style formatting introduced in Python 3.2 is only used on the format string, not the actual log messages.
To enable brace-style formatting on the actual log message, we can monkey-patch a bit of the logger code.
The following patches the logging module to create a get_logger function that will return a logger that uses the new-style formatting for every log record that it handles.
import functools
import logging
import types
def _get_message(record):
"""Replacement for logging.LogRecord.getMessage
that uses the new-style string formatting for
its messages"""
msg = str(record.msg)
args = record.args
if args:
if not isinstance(args, tuple):
args = (args,)
msg = msg.format(*args)
return msg
def _handle_wrap(fcn):
"""Wrap the handle function to replace the passed in
record's getMessage function before calling handle"""
@functools.wraps(fcn)
def handle(record):
record.getMessage = types.MethodType(_get_message, record)
return fcn(record)
return handle
def get_logger(name=None):
"""Get a logger instance that uses new-style string formatting"""
log = logging.getLogger(name)
if not hasattr(log, "_newstyle"):
log.handle = _handle_wrap(log.handle)
log._newstyle = True
return log
Usage:
>>> log = get_logger()
>>> log.warning("{!r}", log)
<logging.RootLogger object at 0x4985a4d3987b>
Notes:
- Fully compatible with normal logging methods (just replace
logging.getLoggerwithget_logger) - Will only affect specific loggers created by the
get_loggerfunction (doesn't break 3rd party packages). - If the logger is accessed again from a normal
logging.getLogger()call, the new-style formatting will still apply. - kwargs are not supported (makes it impossible to conflict with the built-in
exc_info,stack_info,stacklevelandextra). - Performance hit should be minimal (rewriting a single function pointer for each log message).
- The formatting of the message is delayed until it is output (or not at all if the log message is filtered).
- Args are stored on
logging.LogRecordobjects as usual (useful in some cases with custom log handlers). - From looking at the logging module source code it seems like it should work all the way back to Python 2.6 when str.format was introduced (but I've only tested it in 3.5 and up)
回答6:
Try logging.setLogRecordFactory in Python 3.2+:
import collections
import logging
class _LogRecord(logging.LogRecord):
def getMessage(self):
msg = str(self.msg)
if self.args:
if isinstance(self.args, collections.Mapping):
msg = msg.format(**self.args)
else:
msg = msg.format(*self.args)
return msg
logging.setLogRecordFactory(_LogRecord)
回答7:
Here's something real simple that works:
debug_logger: logging.Logger = logging.getLogger("app.debug")
def mydebuglog(msg: str, *args, **kwargs):
if debug_logger.isEnabledFor(logging.DEBUG):
debug_logger.debug(msg.format(*args, **kwargs))
Then:
mydebuglog("hello {} {val}", "Python", val="World")
回答8:
I created a custom Formatter, called ColorFormatter that handles the problem like this:
class ColorFormatter(logging.Formatter):
def format(self, record):
# previous stuff, copy from logging.py…
try: # Allow {} style
message = record.getMessage() # printf
except TypeError:
message = record.msg.format(*record.args)
# later stuff…
This keeps it compatible with various libraries. The drawback is that it is probably not performant due to potentially attempting format of the string twice.
来源：https://stackoverflow.com/questions/13131400/logging-variable-data-with-new-format-string