=========
Metrology
=========

A library to easily measure what's going on in your python.

Metrology allows you to add instruments to your python code and hook them to external reporting tools like Graphite so as to better understand what's going on in your running python program.

Installing
==========

To install : ::

    pip install metrology

API
===

Gauge
-----

A gauge is an instantaneous measurement of a value

.. code-block:: python

    class JobGauge(metrology.instruments.Gauge):
        def value(self):
            return len(queue)
    gauge = Metrology.gauge('pending-jobs', JobGauge())


Counters
--------

A counter is like a gauge, but you can increment or decrement its value

.. code-block:: python

    counter = Metrology.counter('pending-jobs')
    counter.increment()
    counter.decrement()
    counter.count

Meters
------

A meter measures the rate of events over time (e.g., "requests per second").
In addition to the mean rate, you can also track 1, 5 and 15 minutes moving averages

.. code-block:: python

    meter = Metrology.meter('requests')
    meter.mark()
    meter.count

or as a decorator:

.. code-block:: python

    @Metrology.meter('requests')
    def do_this_again():
        # do something

or with context manager:

.. code-block:: python

    with Metrology.meter('requests'):
        # do something

Timers
------

A timer measures both the rate that a particular piece of code is called and the distribution of its duration

.. code-block:: python

    timer = Metrology.timer('responses')
    with timer:
        do_something()

or as a decorator:

.. code-block:: python

    @Metrology.timer('responses')
    def response():
        # do_something


Utilization Timer
-----------------

A specialized timer that calculates the percentage of wall-clock time that was spent

.. code-block:: python

    utimer = Metrology.utilization_timer('responses')
    with utimer:
      do_something()

Tagging metrics
---------------

All metrics can be tagged if the reporter supports it (currently: Graphite, Librato, Logger. The StatsD reporter supports the Datadog tag format because no official tag standard has been devised by the project).
Tags can be arbitrary key-value pairs. Just assign a dict as metric name. A 'name'-entry is required.

.. code-block:: python

    counter = Metrology.counter({
      'name': 'pending-jobs',
      'host': 'backend',
      'priority': 'high'
    })
    counter.increment()
    counter.decrement()
    counter.count

All metric types support tagging.

Reporters
=========

Logger Reporter
---------------

A logging reporter that write metrics to a logger

.. code-block:: python

    reporter = LoggerReporter(level=logging.INFO, interval=10)
    reporter.start()


Graphite Reporter
-----------------

A graphite reporter that send metrics to graphite

.. code-block:: python

    reporter = GraphiteReporter('graphite.local', 2003)
    reporter.start()


Librato Reporter
----------------

A librator metric reporter that send metrics to librato API

.. code-block:: python

    reporter = LibratoReporter("<email>", "<token>")
    reporter.start()


Ganglia Reporter
----------------

A ganglia reporter that sends metrics to gmond.

.. code-block:: python

    reporter = GangliaReporter("Group Name", "localhost", 8649, "udp", interval=60)
    reporter.start()

StatsD Reporter
----------------

A statsd reporter that sends metrics to statsd daemon.

.. code-block:: python

    reporter = StatsDReporter('localhost', 3333, conn_type='tcp')
    reporter.start()

or use default UDP setting:

.. code-block:: python

    reporter = StatsDReporter('localhost', 3333)
    reporter.start()


Acknowledgement
===============

This is heavily inspired by the awesome `metrics <https://github.com/codahale/metrics>`_ library.