Skip to main content

Easy context prefixes for messages.

Project description

Dynamic message prefixes providing execution context.

The primary facility here is Pfx, a context manager which maintains a per thread stack of context prefixes.

Usage is like this:

from cs.pfx import Pfx
def parser(filename):
  with Pfx("parse(%r)", filename):
    with open(filename) as f:
      for lineno, line in enumerate(f, 1):
        with Pfx("%d", lineno) as P:
          if line_is_invalid(line):
            raise ValueError("problem!")
"line = %r", line)

This produces log messages like:

datafile: 1: line = 'foo\n'

and exception messages like:

datafile: 17: problem!

which lets one put just the relevant complaint in exception and log messages and get useful calling context on the output. This does make for wordier logs and exceptions but used with a little discretion produces far more debugable results.

Function gen(func)

Decorator for generators to manage the Pfx stack.

Before running the generator the current stack height is noted. After yield, the stack above that height is trimmed and saved, and the value yielded. On recommencement the saved stack is reapplied to the current stack (which may have changed) and the generator continued.

Class Pfx

A context manager to maintain a per-thread stack of message prefixes.

Function pfx(func)

Decorator for functions that should run inside:

with Pfx(func_name):


def f(...):

Function pfx_iter(tag, iterable)

Wrapper for iterables to prefix exceptions with tag.

Class PfxCallInfo

MRO: Pfx
Subclass of Pfx to insert current function an caller into messages.

Function pfxtag(tag, loggers=None)

Decorator for functions that should run inside:

with Pfx(tag, loggers=loggers):


def f(...):

Function PfxThread(target=None, **kw)

Factory function returning a Thread which presents the current prefix as context.

Function prefix()

Return the current Pfx prefix.

Function PrePfx(tag, *args)

Push a temporary value for Pfx._state._ur_prefix to enloundenify messages.

Function XP(msg, *args, **kwargs)

Variation on cs.x.X which prefixes the message with the currrent Pfx prefix.

Function XX(prepfx, msg, *args, **kwargs)

Trite wrapper for XP() to transiently insert a leading prefix string.


XX("NOTE!", "some message")

Project details

Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Filename, size & hash SHA256 hash help File type Python version Upload date
cs.pfx-20190403.tar.gz (6.4 kB) Copy SHA256 hash SHA256 Source None

Supported by

Elastic Elastic Search Pingdom Pingdom Monitoring Google Google BigQuery Sentry Sentry Error logging AWS AWS Cloud computing DataDog DataDog Monitoring Fastly Fastly CDN SignalFx SignalFx Supporter DigiCert DigiCert EV certificate StatusPage StatusPage Status page