@@ -1,20 +1,23 @@
+pub(super) use decl::crc32;
 pub(crate) use decl::make_module;
+use rustpython_vm::{builtins::PyBaseExceptionRef, convert::ToPyException, VirtualMachine};
 
-pub(super) use decl::crc32;
+const PAD: u8 = 61u8;
+const MAXLINESIZE: usize = 76; // Excluding the CRLF
 
 #[pymodule(name = "binascii")]
 mod decl {
+    use super::{MAXLINESIZE, PAD};
     use crate::vm::{
-        builtins::{PyBaseExceptionRef, PyIntRef, PyTypeRef},
+        builtins::{PyIntRef, PyTypeRef},
+        convert::ToPyException,
         function::{ArgAsciiBuffer, ArgBytesLike, OptionalArg},
         PyResult, VirtualMachine,
     };
     use itertools::Itertools;
 
-    const MAXLINESIZE: usize = 76;
-
     #[pyattr(name = "Error", once)]
-    fn error_type(vm: &VirtualMachine) -> PyTypeRef {
+    pub(super) fn error_type(vm: &VirtualMachine) -> PyTypeRef {
         vm.ctx.new_exception_type(
             "binascii",
             "Error",
@@ -62,15 +65,18 @@ mod decl {
     fn unhexlify(data: ArgAsciiBuffer, vm: &VirtualMachine) -> PyResult<Vec<u8>> {
         data.with_ref(|hex_bytes| {
             if hex_bytes.len() % 2 != 0 {
-                return Err(new_binascii_error("Odd-length string".to_owned(), vm));
+                return Err(super::new_binascii_error(
+                    "Odd-length string".to_owned(),
+                    vm,
+                ));
             }
 
             let mut unhex = Vec::<u8>::with_capacity(hex_bytes.len() / 2);
             for (n1, n2) in hex_bytes.iter().tuples() {
                 if let (Some(n1), Some(n2)) = (unhex_nibble(*n1), unhex_nibble(*n2)) {
                     unhex.push(n1 << 4 | n2);
                 } else {
-                    return Err(new_binascii_error(
+                    return Err(super::new_binascii_error(
                         "Non-hexadecimal digit found".to_owned(),
                         vm,
                     ));
@@ -139,10 +145,6 @@ mod decl {
         newline: bool,
     }
 
-    fn new_binascii_error(msg: String, vm: &VirtualMachine) -> PyBaseExceptionRef {
-        vm.new_exception_msg(error_type(vm), msg)
-    }
-
     #[derive(FromArgs)]
     struct A2BBase64Args {
         #[pyarg(any)]
@@ -177,8 +179,6 @@ mod decl {
             -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1, -1,-1,-1,-1,
         ];
 
-        const PAD: u8 = 61u8;
-
         let A2BBase64Args { s, strict_mode } = args;
         s.with_ref(|b| {
             if b.is_empty() {
@@ -246,34 +246,16 @@ mod decl {
                 }
             }
 
-            return match quad_pos {
+            match quad_pos {
                 0 => Ok(decoded),
-                1 => Err(base64::DecodeError::InvalidLastSymbol(decoded.len() / 3 * 4 + 1, 0)),
-                _ => Err(base64::DecodeError::InvalidLength)
-            };
-        })
-        .map_err(|err| {
-            let python_error = match err {
-                base64::DecodeError::InvalidByte(0, PAD) => {
-                    String::from("Leading padding not allowed")
-                }
-                base64::DecodeError::InvalidByte(_, PAD) => {
-                    String::from("Discontinuous padding not allowed")
-                }
-                base64::DecodeError::InvalidByte(_, _) => {
-                    String::from("Only base64 data is allowed")
-                }
-                base64::DecodeError::InvalidLastSymbol(_, PAD) => {
-                    String::from("Excess data after padding")
-                }
-                base64::DecodeError::InvalidLastSymbol(length, _) => {
-                    format!("Invalid base64-encoded string: number of data characters {} cannot be 1 more than a multiple of 4", length)
-                }
-                base64::DecodeError::InvalidLength => String::from("Incorrect padding"),
-            };
-
-            new_binascii_error(format!("error decoding base64: {python_error}"), vm)
+                1 => Err(base64::DecodeError::InvalidLastSymbol(
+                    decoded.len() / 3 * 4 + 1,
+                    0,
+                )),
+                _ => Err(base64::DecodeError::InvalidLength),
+            }
         })
+        .map_err(|err| super::Base64DecodeError(err).to_pyexception(vm))
     }
 
     #[pyfunction]
@@ -738,3 +720,26 @@ mod decl {
         })
     }
 }
+
+struct Base64DecodeError(base64::DecodeError);
+
+fn new_binascii_error(msg: String, vm: &VirtualMachine) -> PyBaseExceptionRef {
+    vm.new_exception_msg(decl::error_type(vm), msg)
+}
+
+impl ToPyException for Base64DecodeError {
+    fn to_pyexception(&self, vm: &VirtualMachine) -> PyBaseExceptionRef {
+        use base64::DecodeError::*;
+        let message = match self.0 {
+            InvalidByte(0, PAD) => "Leading padding not allowed".to_owned(),
+            InvalidByte(_, PAD) => "Discontinuous padding not allowed".to_owned(),
+            InvalidByte(_, _) => "Only base64 data is allowed".to_owned(),
+            InvalidLastSymbol(_, PAD) => "Excess data after padding".to_owned(),
+            InvalidLastSymbol(length, _) => {
+                format!("Invalid base64-encoded string: number of data characters {} cannot be 1 more than a multiple of 4", length)
+            }
+            InvalidLength => "Incorrect padding".to_owned(),
+        };
+        new_binascii_error(format!("error decoding base64: {message}"), vm)
+    }
+}