logging_extra.py

import logging
logging.basicConfig(level='DEBUG')
_log = logging.getLogger(__name__)
class Ctx:
    def __init__(self, d):
        self.d = d
    def keys(self):
        return self.d.keys()
    def __getitem__(self, item):
        return self.d[item]

ctx = Ctx(dict(a=1, b=2, c={'d': 3}))
_log.info('Hello', extra=ctx)

"""
Traceback (most recent call last):
  File "a.py", line 13, in <module>
    _log.info('Hello', extra=ctx)
  File "/usr/lib64/python2.7/logging/__init__.py", line 1174, in info
    self._log(INFO, msg, args, **kwargs)
  File "/usr/lib64/python2.7/logging/__init__.py", line 1292, in _log
    record = self.makeRecord(self.name, level, fn, lno, msg, args, exc_info, func, extra)
  File "/usr/lib64/python2.7/logging/__init__.py", line 1268, in makeRecord
    for key in extra:
  File "a.py", line 10, in __getitem__
    return self.d[item]
KeyError: 0
"""