Question

I would like some feedback on my first Python script that makes use of OOP style. This is a Munin plugin that graphs average fan speed or average chassis temp depending on the name of the plugin (dell_fans, dell_temps).

An hour or so ago I submitted a procedural version of the fan speed plugin to stackoverflow to get help converting it to an OOP style. I then built off of that to combine the two scripts. Any feedback, suggestions, corrections would be very helpful. I would like to correct any misconceptions I may have before they cement.

Update: Modified to have common base class. Any other suggestions?

import sys
import subprocess

class Statistics(object):

    def __init__(self, command):
        self.command = command.split()

    def average(self):
        data = subprocess.Popen(self.command,stdout=subprocess.PIPE).stdout.readlines()

        count = total = 0
        for item in data:
            if "Reading" in item:
                # Extract variable length fan speed, without regex.
                total += float(item.split(":")[1].split()[0])
                count += 1
        # Sometimes omreport returns zero output if omsa services aren't started.
        if not count or not total:
            raise ValueError("No output from omreport. Is OMSA services started?")

        avg = (total / count)
        return avg

    def print_autoconfig(self):
        print "autoconfig goes here"


class Fanspeed(Statistics):

    def __init__(self, command):
        Statistics.__init__(self, command)

    def print_config(self):
        print "graph_title Average Fan Speed"
        print "graph_args --base 1000 -l 0"
        print "graph_vlabel speed (RPM)"
        print "graph_category Chassis"
        print "graph_info This graph shows the average speed of all fans"
        print "graph_period second"
        print "data.label speed"
        print "data.info Average fan speed for the five minutes."


class Temps(Statistics):

    def __init__(self, command):
        Statistics.__init__(self, command)

    def print_config(self):
        print "graph_title Average Temperature"
        print "graph_args --upper-limit 120 -l 0"
        print "graph_vlabel Celsius"
        print "graph_category Chassis"
        print "graph_info This graph shows the avg temp of all sensors."
        print "graph_period second"
        print "data.label temp"
        print "data.info Average chassis temperature for the five minutes."


if __name__ == '__main__':
    # Munin populates sys.argv[1] with "" (an empty argument), lets remove it.
    sys.argv = [x for x in sys.argv if x]

    if "fans" in sys.argv[0]:
        cmd = "/usr/sbin/omreport chassis fans"
        omdata = Fanspeed(cmd)
    elif "temps" in sys.argv[0]:
        cmd = "/usr/sbin/omreport chassis temps"
        omdata = Temps(cmd)
    else:
        print >> sys.stderr, "Change filename to dell_fans or dell_temps."
        sys.exit(1)

    if len(sys.argv) > 1:
        if sys.argv[1].lower() == "autoconfig":
            omdata.print_autoconfig()
        elif sys.argv[1].lower() == "config":
            omdata.print_config()
    else:
        try:
            average = omdata.average()
            print "data.value %s" % average
        except OSError, e:
            print >> sys.stderr, "Error running '%s', %s" % (cmd, e)
            sys.exit(1)
        except ValueError, e:
            # Sometimes omreport returns zero output if omsa services aren't started.
            print >> sys.stderr, 'Error: "omreport chassis fans" returned 0 output.'
            print >> sys.stderr, 'OMSA running? Try: "srvadmin-services.sh status".'
            sys.exit(1)

Answer 1

Is Temps a FanSpeed? That’s the litmus test for whether subclassing is appropriate (e.g. an elephant is an animal, a car is not an animal – so it might be appropriate to have a subclass of Animal which models an elephant, but not a subclass of Animal which models a car).

It sounds like they’re modelling two different things – so yes, create a common base class for them.