Update documentation, and a bit of the functionality

flask_logging_extras/__init__.py

@@ -16,6 +16,34 @@ __copyright__ = '(c) 2015 GT2'
 class FlaskExtraLogger(logging.getLoggerClass()):
     """
     A logger class that is capable of adding extra keywords to log formatters
+
+    Usage:
+
+    .. code-block:: python
+
+       import logging
+
+       from flask_logging_extras import register_logger_class
+
+       # This must be done before the app is initialized!
+       register_logger_class(cls=FlaskExtraLogger)
+
+       app = Flask(__name__)
+       app.config['FLASK_LOGGING_EXTRAS_KEYWORDS'] = ['category']
+       app.logger.init_app()
+
+       formatter = logging.Formatter(
+           '[%(asctime)s] [%(levelname)s] [%(category)s] %(message)s')
+       handler = logging.FileHandler('app.log', mode='a')
+       handler.setFormatter(formatter)
+       handler.setLevel(logging.INFO)
+
+       app.logger.addHandler(handler)
+
+       app.logger.info('The message', category='my category')
+
+       # This will produce something like this in app.log:
+       # [TIMESTAMP2017-01-16 08:44:48.944] [INFO] [my category] The message
     """
 
     def __init__(self, *args, **kwargs):
@@ -38,11 +66,25 @@ class FlaskExtraLogger(logging.getLoggerClass()):
         super(FlaskExtraLogger, self)._log(*args, **kwargs)
 
     def init_app(self, app):
-        self.app = app
+        """
+        Intialize the logger class with a Flask application
 
-        self.app.config.setdefault('FLASK_LOGGING_EXTRAS_KEYWORDS', [])
+        The class reads its necessary configuration from the config of this
+        application.
 
-        for kw in self.app.config['FLASK_LOGGING_EXTRAS_KEYWORDS']:
+        If the application doesn’t call this, or doesn’t have the
+        `FLASK_LOGGING_EXTRAS_KEYWORDS` in its config, no extra
+        functionality will be added.
+
+        :param app: a Flask application
+        :type app: Flask
+        :raises ValueError: if the app tries to register a keyword that is
+                             reserved for internal use
+        """
+
+        app.config.setdefault('FLASK_LOGGING_EXTRAS_KEYWORDS', [])
+
+        for kw in app.config['FLASK_LOGGING_EXTRAS_KEYWORDS']:
             if kw in ['exc_info', 'extra', 'stack_info']:
                 raise ValueError(
                     '"{keyword}" member of FLASK_LOGGING_EXTRAS_KEYWORDS is '
@@ -53,15 +95,30 @@ def register_logger_class(cls=FlaskExtraLogger):
     """
     Register a new logger class
 
-    It is effectively a wrapper around logging.setLoggerClass(), with an
+    It is effectively a wrapper around `logging.setLoggerClass()`, with an
     added check to make sure the class can be used as a logger.
 
     To use the extra features of the logger class in a Flask app, you must
     call it before the app is instantiated.
+
+    This function returns the logger class that was the default before
+    calling.  This might be useful if you only want to use `cls` in the
+    Flask app object, but not anywhere else in your code.  In this case,
+    simply call `register_logger_class()` again with the return value from
+    the first invocation.
+
+    :param cls: a logger class to register as the default one
+    :type cls: class(logging.Logger)
+    :returns: the old default logger class
+    :rtype: class
+    :raises TypeError: if the class is not a subclass of `logging.Logger`
     """
 
     if not issubclass(cls, logging.Logger):
         raise TypeError(
             "The logger class must be a subclass of logging.Logger!")
 
+    old_class = logging.get_logger_class()
     logging.setLoggerClass(cls)
+
+    return old_class