diff --git a/nac3core/src/top_level.rs b/nac3core/src/top_level.rs
index ade98dd1..681700be 100644
--- a/nac3core/src/top_level.rs
+++ b/nac3core/src/top_level.rs
@@ -10,7 +10,7 @@ use itertools::Itertools;
 use parking_lot::{Mutex, RwLock};
 use rustpython_parser::ast::{self, Stmt};
 
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Copy)]
+#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Copy, Hash)]
 pub struct DefinitionId(pub usize);
 
 pub enum TopLevelDef {
@@ -462,9 +462,9 @@ impl TopLevelComposer {
     }
 
     /// step 3, class fields and methods
-    // FIXME: need analyze base classes here
-    // FIXME: how to deal with self type
-    // FIXME: how to prevent cycles
+    // FIXME: analyze base classes here
+    // FIXME: deal with self type
+    // NOTE: prevent cycles only roughly done
     fn analyze_top_level_class_fields_methods(&mut self) -> Result<(), String> {
         let mut def_ast_list = self.definition_ast_list.write();
         let converted_top_level = &self.to_top_level_context();
@@ -472,20 +472,27 @@ impl TopLevelComposer {
         let to_be_analyzed_class = &mut self.to_be_analyzed_class;
         let unifier = &mut self.unifier;
 
+        // NOTE: roughly prevent infinite loop
+        let mut max_iter = to_be_analyzed_class.len() * 4;
         'class: loop {
-            if to_be_analyzed_class.is_empty() {
+            if to_be_analyzed_class.is_empty() && { max_iter -= 1; max_iter > 0 } {
                 break;
             }
 
             let class_ind = to_be_analyzed_class.remove(0).0;
-            let (class_name, class_body, class_resolver) = {
+            let (class_name,
+                class_body_ast,
+                class_bases_ast,
+                class_resolver,
+                class_ancestors
+            ) = {
                 let (class_def, class_ast) = &mut def_ast_list[class_ind];
                 if let Some(ast::Located {
-                    node: ast::StmtKind::ClassDef { name, body, .. }, ..
+                    node: ast::StmtKind::ClassDef { name, body, bases, .. }, ..
                 }) = class_ast.as_ref()
                 {
-                    if let TopLevelDef::Class { resolver, .. } = class_def.write().deref() {
-                        (name, body, resolver.as_ref().unwrap().clone())
+                    if let TopLevelDef::Class { resolver, ancestors, .. } = class_def.write().deref() {
+                        (name, body, bases, resolver.as_ref().unwrap().clone(), ancestors.clone())
                     } else {
                         unreachable!()
                     }
@@ -494,11 +501,35 @@ impl TopLevelComposer {
                 }
             };
 
+            let all_base_class_analyzed = {
+                let not_yet_analyzed = to_be_analyzed_class.clone().into_iter().collect::<HashSet<_>>();
+                let base = class_ancestors.clone().into_iter().collect::<HashSet<_>>();
+                let intersection = not_yet_analyzed.intersection(&base).collect_vec();
+                intersection.is_empty()
+            };
+            if !all_base_class_analyzed {
+                to_be_analyzed_class.push(DefinitionId(class_ind));
+                continue 'class;
+            }
+
+            // get the bases type, can directly do this since it
+            // already pass the check in the previous stages
+            let class_bases_ty = class_bases_ast
+                .iter()
+                .filter_map(|x| {
+                    class_resolver.as_ref().lock().parse_type_annotation(
+                        converted_top_level,
+                        unifier.borrow_mut(),
+                        primitives,
+                        x).ok()
+                })
+                .collect_vec();
+
             // need these vectors to check re-defining methods, class fields
             // and store the parsed result in case some method cannot be typed for now
             let mut class_methods_parsing_result: Vec<(String, Type, DefinitionId)> = vec![];
             let mut class_fields_parsing_result: Vec<(String, Type)> = vec![];
-            for b in class_body {
+            for b in class_body_ast {
                 if let ast::StmtKind::FunctionDef {
                     args: method_args_ast,
                     body: method_body_ast,