'Initialize the adapter with a logger and a dict-like object which
provides contextual information. This constructor signature allows
easy stacking of LoggerAdapters, if so desired.
You can effectively pass keyword arguments as shown in the
following example:
adapter = LoggerAdapter(someLogger, dict(p1=v1, p2="v2"))'

def __init__(self, logger, extra):

    self.logger = logger
    self.extra = extra
