In Lithoxyl’s system of instrumentation, Actions are used to carry messages, data, and timing metadata through the Loggers to their destination, the Sinks. This chapter focuses in on this last step.
Writing a simple Sink¶
Sinks can grow to be very involved, but a useful Sink can be as simple as:
import sys class DotSink(object): def on_end(self, end_event): sys.stdout.write('.') sys.stdout.flush()
Note that our new Sink does not have to inherit from any special
object. DotSink is a correct and capable Sink, ready to be
instantiated and installed with
Logger.add_sink(), just like in
the overview. Once added to your Logger,
every time an Action ends, a dot will be written out to your console.
In this example,
on_end is the handler for just one of Lithoxyl’s
events. The next section takes a look at all five of them.
Lithoxyl Events are state changes associated with a particular Action. Five types of events can happen in the Lithoxyl system:
begin - The beginning of an Action, whether manually or through entering a context-managed block of code.
The begin event corresponds to the method signature
on_begin(self, begin_event). Designed to be called once per Action.
end - The completion of an Action, whether manually (
failure()) or through exiting a context-managed block of code. There are three ways an Action can end, success, failure, and exception, but all of them result in an end event.
The end event corresponds to the method signature
on_end(self, end_event). Designed to be called once per Action.
exception - Called immediately when an exception is raised from within the context-managed block, or when an exception is manually handled with Action.exception(). Actions ending in exception state typically fire two events, one for handling the exception, and one for ending the Action.
The exception event corresponds to the Sink method signature
on_exception(self, exc_event, exc_type, exc_obj, exc_tb). Designed to be called up to once.
warn - The registration of a warning within an Action.
Corresponds to the Sink method signature
on_warn(self, warn_event). Can be called an arbitrary number of times.
comment - The registration of a comment from a Logger. Comments are used for publishing metadata associated with a Logger.
The comment event corresponds to the Sink method signature
on_comment(self, comment_event). See here for more about comments. Can be called an arbitrary number of times.
A Sink handles the event by implementing the respective method. The event objects that accompany every event are meant to be practically immutable; their values are set once, at creation.