Check a Python AST for a few issues I'd like to avoid

AstCheck.py

from ast import Name, NodeTransformer, parse, Return
from itertools import chain
import sys
from warnings import warn


class StaticTransformer(NodeTransformer):

    def _check_none(self, x):
        if isinstance(x, Name) and x.id == 'None':
            warn("Passing None Argument to function", RuntimeWarning)

    def visit_FunctionDef(self, node):
        self.generic_visit(node)
        if not all([isinstance(x, Return) for x in node.body]):
            warn("Returning None from function %s" % node.name, RuntimeWarning)
        return node

    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
            self._check_none(x)
        return node

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