I’m learning a little Python for a side project. I wrote a SELECT statement that would produce NULLs and rather than use COALESCE to prevent returning NULLs, I wanted the application to be able to detect and then replace the value with a default.

In Perl, this is a no-brainer to me – the NULL value would be ‘undef’, and I could write something like:

$value = $default if (! defined $value);

So, after a bit of struggling, I found out that the ‘None’ object is returned when a value is NULL in python.

To determine whether you’ve got a NULL, you write something like:

if $value is None:
    $value = $default

Generally speaking, Python considers an undefined object to be a rare occurrence.

Here are the slides from my PDX.pm talk this week. A link to the accompanying podcast will be along soon.

Other fun things we discussed at the meeting:
Cisco::Reconfig
trapgen
logger
logwatch

Thanks for the lively discussion!

[edit] podcast!

[edit] Clarification of two items from the podcast:
- multiline messages do indeed come in multiple packets. There is a message counter that increments for each message, so you could use the host name + message counter to match up multi-line messages. For what I’m doing, the important part is in that first line, so the payoff isn’t worth the investment.
- re hypens in the mnemonic field of the system message: I went back through and wasn’t able to find any examples of this, so I retract my statement. (I do have examples of system messages with hyphens in the facility field.)

You need:
root/sudo access to a statically-addressed Ubuntu machine.  (It will need to be on whenever your router is on in order to get anything good out of this.) This is your log host.
Enable access to your Cisco router.

Part 1: Set up your log host.

Step 1: before editing any of the files discussed below, be sure to back them up, e.g.:
cp /etc/syslog.conf /etc/syslog.conf.dontmessthisup

Step 2: edit /etc/syslog.conf to include this:
#router logging
local6.debug                    /var/log/cisco.log

This means “send all messages from facility local6, with a priority of debug or greater, to /var/log/cisco.log”.

(Note that the default facility for Cisco is local7; if you want/need to use the Cisco default, change the above accordingly.)

Step 3: create the log file I specified above:
sudo touch /var/log/cisco.log
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