diff --git a/androscalpel/src/code.rs b/androscalpel/src/code.rs
index 94d1dae..72456f9 100644
--- a/androscalpel/src/code.rs
+++ b/androscalpel/src/code.rs
@@ -101,10 +101,8 @@ impl Code {
             strings.extend(ins.get_all_strings());
         }
         if let Some(names) = &self.parameter_names {
-            for name in names {
-                if let Some(name) = name {
-                    strings.insert(name.clone());
-                }
+            for name in names.iter().flatten() {
+                strings.insert(name.clone());
             }
         }
         strings
diff --git a/androscalpel/src/instructions.rs b/androscalpel/src/instructions.rs
index 70a2a3b..f7f044c 100644
--- a/androscalpel/src/instructions.rs
+++ b/androscalpel/src/instructions.rs
@@ -14907,7 +14907,7 @@ impl InvokeVirtual {
                 vd,
                 vf,
                 vg,
-                b: meth_idx as u16,
+                b: meth_idx,
             }
         } else if consec && len <= 255 {
             let a = self.args.len() as u8;
diff --git a/androscalpel/src/lib.rs b/androscalpel/src/lib.rs
index 3ece94a..c8bdb61 100644
--- a/androscalpel/src/lib.rs
+++ b/androscalpel/src/lib.rs
@@ -1,3 +1,6 @@
+#![allow(clippy::unnecessary_fallible_conversions)]
+// DexString has Into<String> but it's only for
+// python, TryInto should be prefered
 use anyhow::Result;
 
 use pyo3::prelude::*;
diff --git a/androscalpel/src/py_utils.rs b/androscalpel/src/py_utils.rs
index 2d7a61a..9a641a1 100644
--- a/androscalpel/src/py_utils.rs
+++ b/androscalpel/src/py_utils.rs
@@ -3,11 +3,15 @@
 use pyo3::prelude::*;
 use pyo3::types::PyBytes;
 
-use std::io::Cursor;
+use std::collections::HashSet;
+use std::io::{Cursor, Seek, SeekFrom};
 use std::path::PathBuf;
 
-use crate::Result;
-use androscalpel_serializer::{Serializable, Sleb128, Uleb128, Uleb128p1};
+use crate::{Apk, IdType, Result};
+use androscalpel_serializer::{
+    DexFileReader, HeaderItem, Serializable, Sleb128, Uleb128, Uleb128p1,
+};
+use apk_frauder::{end_of_central_directory::EndCentralDirectory, ZipFileReader};
 
 /// Convert an integer to the uleb128 byte encoding
 #[pyfunction]
@@ -44,6 +48,46 @@ pub fn sleb128_to_int(b: &[u8]) -> Result<i32> {
     Ok(Sleb128::deserialize_from_slice(b)?.0)
 }
 
+// TODO: list_defined_classes, is_dex, is_zip take &[u8], but should allow to also read from file
+
+/// List all classes defined in a dex file.
+#[pyfunction]
+pub fn list_defined_classes(dex: &[u8]) -> Result<HashSet<IdType>> {
+    let dex = DexFileReader::new(dex)?;
+    dex.get_class_defs()
+        .iter()
+        .map(|cdef| Apk::get_id_type_from_idx(cdef.class_idx as usize, &dex))
+        .collect()
+}
+
+/// Test if a file is as .dex file an return the dex version if it is, else return None.
+#[pyfunction]
+pub fn is_dex(file: &[u8]) -> Option<usize> {
+    HeaderItem::deserialize_from_slice(file)
+        .ok()
+        .and_then(|header| String::from_utf8(header.magic.version.to_vec()).ok())
+        .and_then(|version| version.parse::<usize>().ok())
+}
+
+/// Test if a file is a zip file.
+#[pyfunction]
+pub fn is_zip(file: &[u8]) -> bool {
+    let mut file = Cursor::new(file);
+    let ecd_off = if let Some(off) = ZipFileReader::get_end_of_central_directory_offset(&mut file) {
+        off
+    } else {
+        return false;
+    };
+    if file.seek(SeekFrom::Start(ecd_off)).is_err() {
+        return false;
+    }
+    if let Ok(sig) = apk_frauder::Signature::deserialize(&mut file) {
+        EndCentralDirectory::SIGNATURE == sig
+    } else {
+        false
+    }
+}
+
 /// Replace the dex files a an apk an resigned the apk.
 ///
 /// # Warning