[Python-Dev] Change to logging Formatters: support for alternative format styles (original) (raw)

Nick Coghlan ncoghlan at gmail.com
Tue Oct 26 13:08:24 CEST 2010

On Tue, Oct 26, 2010 at 12:28 AM, Vinay Sajip <vinay_sajip at yahoo.co.uk> wrote:

Comments welcome. Assuming there are no strong objections asking for reversion of this change, I'll publicise to the wider community in a few days.

It strikes me as a solid, pragmatic solution to a thorny problem.

Looking at your checkin though, I wonder if it might be worth implementing some little formatting style classes to get rid of the if/elif chains from the Formatter code. Something like:

Style objects

class PercentStyle(object): default_format = "%(message)" def is_asctime_in_format(fmt): return fmt.find("%(asctime)") >= 0 def format_record(fmt, record): return fmt % record.dict

class StrFormatStyle(object): default_format = "{message}" def is_asctime_in_format(fmt): return fmt.find("{asctime}") >= 0 def format_record(fmt, record): return fmt.format(**record.dict)

from string import Template # Top level, embedding may cause import deadlock issues class StringTemplateStyle(object): def init(self): self._fmt = self._tmpl = None # Setup for format_record default_format = "${message}" def is_asctime_in_format(fmt): return fmt.find("$asctime") >= 0 or fmt.find("${asctime}") >= 0 def format_record(fmt, record): if fmt != self._fmt: self._fmt = fmt self._tmpl = Template(fmt) return self._tmpl.substitute(**record.dict)

Build style map

_STYLE_CODES = tuple("% { $".split()) _STYLES = PercentStyle, StrFormatStyle, StringTemplateStyle _STYLE_MAP = dict(zip(_STYLE_CODES, _STYLES))

Interpretation of the style parameter in Formatter.init

if style not in _STYLE_CODES:

Preserve option to allow arbitrary style objects at some point in the future

raise ValueError("Style must be one of {!r}".format(_STYLE_CODES)) self._style = _STYLE_MAPstyle

self._fmt initialisation if/elif chain replacement

self._fmt = self._style.default_format

Time check if/elif chain replacement

result = self._style.is_asctime_in_format(self._fmt)

Record formatting if/elif chain replacement

s = self._style.format_record(self._fmt, record)

Cheers, Nick.

-- Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia

More information about the Python-Dev mailing list