In Python 3.3.0 and 3.2.3:

>>> from inspect import *
>>> def f(a,b):pass
...
>>> formatargspec(getargspec(f))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/inspect.py", line 905, in formatargspec
    spec = formatargandannotation(arg)
  File "/Library/Frameworks/Python.framework/Versions/3.3/lib/python3.3/inspect.py", line 898, in formatargandannotation
    if arg in annotations:
TypeError: unhashable type: 'list'

No such error in 2.7.1:

>>> formatargspec(getargspec(f))
'((a, b), None, None, None)'