Method returns self?

[Roy Smith]

I've got a data file parser that returns a data object.  You call it 
something like this:

parser = myParser()
data = parser.parse(filename)

Now, I want to give the data class a verify() method.  The parser only 
ensures that the data file has a parsable syntax, but there are also a 
number of higher-level semantic checks that we might want to do.  I have in 
mind something that you would call like this:

parser = myParser()
try:
   data = parser.parse(filename).verify()
except data.VerifyError:
   print "you bozo"

The idea is that verify() is a method of the data class which either 
returns self, or raises an exception.  The code would look something like:

class data:
   def verify (self):
      if everthing is cool:
         return self
      else:
         raise VerifyError

My question is, will I run into garbage collection or reference count 
problems if a method returns self?  I can't quite put my finger on it, but 
I have this vague feeling I might end up with a self-referential object.

Now, I realize, I could just have it return None instead of self, and then 
use it like:

parser = myParser()
data = parser.parse(filename)
try:
   data.verify()
except data.VerifyError:
   print "you bozo"

This would avoid the problem entirely, but it's not as interesting to think 
about :-)