question about list extension

[J]

Ok... I know pretty much how .extend works on a list... basically it
just tacks the second list to the first list... like so:

>>> lista=[1]
>>> listb=[2,3]
>>> lista.extend(listb)
>>> print lista;
[1, 2, 3]

what I'm confused on is why this returns None:

>>> lista=[1]
>>> listb=[2,3]
>>> print lista.extend(listb)
None
>>> print lista
[1, 2, 3]

So why the None? Is this because what's really happening is that
extend() and append() are directly manipulating the lista object and
thus not actuall returning a new object?

Even if that assumption of mine is correct, I would have expected
something like this to work:

>>> lista=[1]
>>> listb=[2,3]
>>> print (lista.extend(listb))
None

The reason this is bugging me right now is that I'm working on some
code.  My program has a debugger class that takes a list as it's only
(for now) argument.  That list, is comprised of messages I want to
spit out during debug, and full output from system commands being run
with Popen...

So the class looks something like this:

class debugger():
    def printout(self,info):
        for line in info:
            print "DEBUG: %s" % line


and later on, it get's called like this

meminfo = Popen('cat
/proc/meminfo',shell=True,stdout=PIPE).communicate[0].splitlines()

if debug:
    debugger.printout(meminfo)

easy enough....

BUT, what if I have several lists I want to pass on multiple lists...

So changing debugger.printout() to:

   def printout(self,*info):

lets me pass in multiple lists... and I can do this:

   for tlist in info:
       for item in tlist:
            print item

which works well...

So, what I'm curious about, is there a list comprehension or other
means to reduce that to a single line?

I tried this, which didn't work because I'm messing up the syntax, somehow:

def func(*info)
    print [ i for tlist in info for i in tlist ]

so can someone help me understand a list comprehension that will turn
those three lines into on?

It's more of a curiosity thing at this point...  and not a huge
difference in code... I was just curious about how to make that work.

Cheers,

Jeff