Fix relative imports and error handling

This deals with relative imports in visit_ImportFrom.  Also adds
try/except around ast.parse() call to catch any files with non-valid
source or syntax errors.

bandit/manager.py

@@ -60,7 +60,11 @@ class BanditManager():
     def _execute_ast_visitor(self, fname, fdata, b_ma, b_rs, b_ts):
         if fdata != None:
             res = b_node_visitor.BanditNodeVisitor(fname, self.logger, b_ma, b_rs, b_ts)
-            res.visit(ast.parse("".join(fdata.readlines())))
+            try:
+                res.visit(ast.parse("".join(fdata.readlines())))
+            except SyntaxError as e:
+                self.logger.error("syntax error while parsing AST from file: %s" % fname)
+                sys.exit(2)
 
     def _init_logger(self, debug=False):
         log_level = logging.INFO

bandit/node_visitor.py

@@ -82,6 +82,8 @@ class BanditNodeVisitor(ast.NodeVisitor):
     def visit_ImportFrom(self, node):
         self.context['lineno'] = node.lineno
         module = node.module
+        if module is None:
+            return self.visit_Import(node)
         for nodename in node.names:
             if nodename.asname:
                 self.context['import_aliases'][nodename.asname] = module + "." + nodename.name

examples/imports-from.py

@@ -1 +1,7 @@
 from subprocess import Popen
+
+from ..foo import sys
+from . import sys
+from .. import sys
+from .. import subprocess
+from ..subprocess import Popen