Beginnings of a python analyzer

Analyzing the source code your running is a massive task. An enormous amount of effort goes into search for and fixing software faults. One thing I've always wondered is how would an analyzer (static or runtime) look if it were examining python. Being a dynamically typed language, python can be extremely tricky to analyze from just its syntax. However, thanks to Armin Ronacher it does have one excellent feature which could allow deeper analysis; direct access to a parsed ast. With this module you can examine, manipulate or mangle the language any way you see fit.
I've decided to attack the number one bug creator in my opinion, passing None to a function. If this were C, that would be like passing NULL. I can't really see why there would be a good place to do that and in my experiences its usually causing a bug. Beyond the basic reasons, its just semantically wrong to be passing around nothing. It sort of defeats the point of providing arguments at all. In python, we've got really nice default argument syntax so if you must have None for a argument, make that the default and don't pass anything. If you can't avoid this due to some API then I'm sorry.
Anyway, here's how I went after it; first I created a class which extends NodeTransformer and added this method:

def visit_Call(self, node):        
 self.generic_visit(node)        
 for x in chain(node.args, node.keywords):            
  x = x.value if hasattr(x, 'value') else x            
  if isinstance(x, Name) and x.id == 'None':            
   warn("Passing None Argument to function", RuntimeWarning)
 return node

Then I just use that method in a simple function to create the ast and walk it:

with open(sys.argv[1]) as f:    
 source = f.read()    
 ast = parse(source, sys.argv[1])    
 node = StaticTransformer().visit(ast)

Now when I call this script and pass in any compilable Python code, if there are any warnings I'll know about them and be able to fix them before the code gets used elsewhere. It is easy to add more methods to check ast nodes, you just follow the visit_<Node> pattern for naming the functions in your NodeTransformer class. I've created a gist with the code that I've written so far, feel free to fork and contribute!