Code Analysis: Give pass to 'volatility3'

Also moves some code into a private method with a docstring in the
visitor class.

test/volatility3_code_analysis.py

@@ -165,13 +165,16 @@ class ModuleVisitor(NodeVisitor):
     def violations(self):
         return self._violations
 
-    def enter_ImportFrom(self, node: ast.ImportFrom):
-        if not node.module:
-            return
-
+    def _check_vol3_import_from(self, node: ast.ImportFrom):
+        """
+        Ensure that the only thing imported from a volatility3 module (apart
+        from the root volatility3 module) are functions and modules. This
+        prevents re-exporting of classes and variables from modules that use
+        them.
+        """
         if (
             node.module
-            and node.module.startswith("volatility3")
+            and node.module.startswith("volatility3.") # Give a pass to volatility3 module
             and node.module != "volatility3.framework.constants._version" # make an exception for this
         ):
             for name in node.names:
@@ -198,6 +201,10 @@ class ModuleVisitor(NodeVisitor):
                         )
                     )
 
+    def enter_ImportFrom(self, node: ast.ImportFrom):
+        self._check_vol3_import_from(node)
+
+
     def enter_ClassDef(self, node: ast.ClassDef) -> Any:
         logger.debug("Entering class %s", node.name)
         clazz = None