Weird exception in my, um, exception class constructor

[Joel Koltner]

I have a generic (do nothing) exception class that's coded like this:

class MyError(exceptions.Exception):
    def __init__(self,args=None):
        self.args = args

When I attempt to raise this exception via 'raise MyError' I get an exception 
within the MyError constructor __init__ as follows:

Traceback (most recent call last):
[lines deleted]
  File "c:\Documents and Settings\Joel.Kolstad\My Documents\Python\
MyStuff.py", line 7, in __init__
    self.args = args
TypeError: 'NoneType' object is not iterable

Ummm... why should 'args' have to be iterable anyway?  I don't understand 
what's going on here?  Could someone help me with this?

I've found empirically that I can write:

    if args self.args = args

...and everything *appears* to work OK, but I'd really like to know what the 
core problem is.

Thank you,
---Joel