context_log.py

"""Ultra-minimalist logger with context

e.g.:
from context_log import Log
Log.out = open('report.txt')
Log.formatter = lambda dictionary: "%(filename)s>%(lineno)03d: %(session)s:  %message" % dictionary

Log.context['session'] = 'Cammping Trip'

Log.warn("There's a bear behind you")
# example.py>7: Camping Trip: There's a bear behind you

Log.debug("jk")
# example.py>10: Camping Trip: jk
"""

import threading, sys, json, os

class Logger(object):
    def __init__(self):
        self.event_types = {
            'INFO': 0, 
            'DEBUG': 1, 
            'WARNING': 5,
            'WARN': 5,
            'ERROR': 10
        }
        self.universal = {}
        self._context_dicts = {}
        self.config() #Initialize
        
    def config(self, event_types={}, minimum=5, out=sys.stdout, formatter=json.dumps):
        """Configure a batch of parameters. You can also change the attributes manually."""
        self.event_types.update(event_types)
        self.minimum = event_types[minimum] if isinstance(minimum, basestring) else minimum
        self.formatter = formatter
        self.out = out
    
    def __getattr__(self,  name):
        if name == "context":
            return self._context_dicts.setdefault(threading.current_thread(), {})
        elif name.upper() in self.event_types:
            def output(event="", **kwargs):
                if self.event_types[name.upper()] >= self.minimum:
                    _dict = dict(
                        self.universal.items() +
                        self.context.items() +
                        kwargs.items() +
                        zip(('filename', 'lineno', 'func_name'), findCaller()) +
                        {'event': event, 'type': name.upper()}.items()
                    )
                    self.out.write(str(self.formatter(_dict))+'\n')
            return output
        else:
            raise AttributeError(name+" is not in event_types")    

# Pulled from logging.py in the stdlib
def findCaller():
    """Find the stack frame of the caller so that we can note the source file name, line number and function name."""
    f = sys._getframe().f_back
    rv = "(unknown file)", 0, "(unknown function)"
    while hasattr(f, "f_code"):
        co = f.f_code
        filename = co.co_filename.rsplit('.',1)[0].lower()
        _this_file = __file__.rsplit('.',1)[0].lower()
        if filename == _this_file:
            f = f.f_back
        else:
            rv = (os.path.basename(co.co_filename), f.f_lineno, co.co_name)
            break
    return rv

Log = Logger() #IMPORT THIS! Using one instance for all modules is what gives us persistent context