Creating the python display is easy, but not quite as easy as writing a client. Unfortunately, none of the packages are built by default in the online release (yet). They have been requested for release, but it will take a while before they end up on the online system.

• Build the sharable libraries required for python
• Setup for python running
• Write the python code

Please note: The display does not have to be run inside the online system. However, if you decide that you want this display to be part of the shifters standard utilities -- and it must run even if the online offline connection is cut, you'll have to do something special (but documented!)..

Build the sharable libraries required for python

See this web page.

Setup for python running

See this web page

Write the Python Code

Below describes how to write a very simple test program that will generate a monitor item. You can use this pattern to integrate monitor information into a more complex monitor program.

import l3xmonitor_util_module
import time

disp = l3xmonitor_util_module.monitor_display_relay()
test_item = disp.get_item("tester", "count")

while 1:
  disp.query_monitor_server()
  if len(test_item) == 0:
    print "No data from the MS"
  else:
    print "Count value is %s" % test_item[0]
  time.sleep(1)

Short explanation of the relevant lines of code:

• import l3xmonitor_util_module This line imports the module that contains the interface code.
• disp = l3xmonitor_util_module.monitor_display_relay() This creates a connection to the Monitor Server relay. The Relay makes information availible both inside and outside the online ACL wall. If you want to run in the online system even if the offline network is down, then use monitor_display_direct instead of monitor_display_relay. BUT, you'll not be able to use the same code offline now. In my code I often default to using the direct connection, and if -r is passed then I use the relay. YMMV.
• test_item = disp.get_item("tester", "count") This creates a container for the monitor server information. In this case, we are requesting the monitor server item count from the monitor server client named tester.
• disp.query_monitor_server() This causes the request for data to be sent to the MS, and the program will block until the information comes back. All containers associated with disp will be filled with data (or error stuff).
• len(test_item) A short explaination on how monitoring works. The MS is desiged so that the same client can be running in many different places (for example, each of the front end crate L3 SBC's generates monitor information). The container test_item is not a single variable, but an array, one entry for ever machine that is generating these results. If nothing comes back from the MS (for example, your monitor client is not running) you have to protect yourself; hence the test on this line of code. Use the python keys call to see a list of all machines that generated monitor information. The order is not always the same from one call to another.
• test_item[0] This returns the actual data in the 0th entry, or first machine to report. Using the machine name as an index is also ok -- for example test_item['d0lx002'] will get the data generated by d0lx002 for client name tester and item count.

A More Complex Example

Often the data that comes back from the monitor server contains XML that needs to be further parsed. This example shows how to write a small bit of python code that gets the And/Or term fire rate for a particular term from the TFW monitor information.

Download the file test.py and put it on the online system. To get it to work, do the following:

setup D0RunII p15.02.03
setup python
python test.py

You should see output that looks like the following:

d0ol40.fnal.gov> python test.py
/d0dist/dist/releases/p15.02.03/lib/Linux2.4-GCC_3_1/l3xmonitor_util_module.py:2: RuntimeWarning: Python C API version mismatch for module l3xmonitor_util_modulec: This Python has API version 1011, module l3xmonitor_util_modulec has version 1010.
import l3xmonitor_util_modulec
207 47712.4
207 47712.6
207 47712.6
207 47712.4
207 47712.4
207 47712.6

The error is due to a new version of python in a release built against an older version of python. It can safely be ignored, and when a newer release built against a more modern version of python appears this will go away of its own accord. You can also build the monitor module on your own if you like.

The python parsing code is fairly simple. The instructions for accessing the XML DOM and the minidom parser can be found on the python documentation site.