diff --git a/.travis.yml b/.travis.yml
index aff28cd6a..be1a47aa2 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -111,6 +111,8 @@ matrix:
           - target
       script:
         - tests/.travis-runner.sh
+      # Only do code coverage on master via a cron job.
+      if: branch = master AND type = cron
       env:
         - TRAVIS_RUST_VERSION=nightly
         - REGULAR_TEST=false
diff --git a/tests/snippets/dict.py b/tests/snippets/dict.py
index 4545f7f58..c453cff2b 100644
--- a/tests/snippets/dict.py
+++ b/tests/snippets/dict.py
@@ -52,6 +52,10 @@ assert ('d', 3) == next(it)
 with assertRaises(StopIteration):
     next(it)
 
+with assertRaises(KeyError) as cm:
+    del x[10]
+assert cm.exception.args[0] == 10
+
 # Iterating a dictionary is just its keys:
 assert ['a', 'b', 'd'] == list(x)
 
@@ -95,9 +99,6 @@ x[7] = 7
 x[2] = 2
 x[(5, 6)] = 5
 
-with assertRaises(KeyError):
-    x["not here"]
-
 with assertRaises(TypeError):
     x[[]] # Unhashable type.
 
@@ -167,19 +168,42 @@ assert y == {'a': 2, 'b': 12, 'c': 19, 'd': -1}
 y.update(y)
 assert y == {'a': 2, 'b': 12, 'c': 19, 'd': -1}  # hasn't changed
 
+# KeyError has object that used as key as an .args[0]
+with assertRaises(KeyError) as cm:
+    x['not here']
+assert cm.exception.args[0] == "not here"
+with assertRaises(KeyError) as cm:
+    x.pop('not here')
+assert cm.exception.args[0] == "not here"
+
+with assertRaises(KeyError) as cm:
+    x[10]
+assert cm.exception.args[0] == 10
+with assertRaises(KeyError) as cm:
+    x.pop(10)
+assert cm.exception.args[0] == 10
+
+class MyClass: pass
+obj = MyClass()
+
+with assertRaises(KeyError) as cm:
+    x[obj]
+assert cm.exception.args[0] == obj
+with assertRaises(KeyError) as cm:
+    x.pop(obj)
+assert cm.exception.args[0] == obj
+
 x = {1: 'a', '1': None}
 assert x.pop(1) == 'a'
 assert x.pop('1') is None
 assert x == {}
 
-with assertRaises(KeyError):
-    x.pop("not here")
-
 x = {1: 'a'}
 assert (1, 'a') == x.popitem()
-with assertRaises(KeyError):
-    x.popitem()
 assert x == {}
+with assertRaises(KeyError) as cm:
+    x.popitem()
+assert cm.exception.args == ('popitem(): dictionary is empty',)
 
 x = {'a': 4}
 assert 4 == x.setdefault('a', 0)
diff --git a/tests/snippets/mappingproxy.py b/tests/snippets/mappingproxy.py
index 624bf6d5f..254f2a925 100644
--- a/tests/snippets/mappingproxy.py
+++ b/tests/snippets/mappingproxy.py
@@ -9,8 +9,10 @@ class A(dict):
 
 
 assert A.__dict__['a'] == A.a
-with assertRaises(KeyError):
-    A.__dict__['not_here']
+with assertRaises(KeyError) as cm:
+    A.__dict__['not here']
+
+assert cm.exception.args[0] == "not here"
 
 assert 'b' in A.__dict__
 assert 'c' not in A.__dict__
diff --git a/tests/snippets/memoryview.py b/tests/snippets/memoryview.py
new file mode 100644
index 000000000..ebf27a9a6
--- /dev/null
+++ b/tests/snippets/memoryview.py
@@ -0,0 +1,6 @@
+
+obj = b"abcde"
+a = memoryview(obj)
+assert a.obj == obj
+
+assert a[2:3] == b"c"
diff --git a/tests/snippets/stdlib_io.py b/tests/snippets/stdlib_io.py
index e6da760d2..08786c219 100644
--- a/tests/snippets/stdlib_io.py
+++ b/tests/snippets/stdlib_io.py
@@ -1,4 +1,5 @@
 from io import BufferedReader, FileIO
+import os
 
 fi = FileIO('README.md')
 bb = BufferedReader(fi)
@@ -14,3 +15,9 @@ with FileIO('README.md') as fio:
 	assert len(result) <= 8*1024
 	assert len(result) >= 0
 	assert isinstance(result, bytes)
+
+fd = os.open('README.md', os.O_RDONLY)
+
+with FileIO(fd) as fio:
+	res2 = fio.read()
+	assert res == res2
diff --git a/tests/snippets/stdlib_os.py b/tests/snippets/stdlib_os.py
index ef9b9111d..d2e39c1ce 100644
--- a/tests/snippets/stdlib_os.py
+++ b/tests/snippets/stdlib_os.py
@@ -244,7 +244,7 @@ with TestWithTempDir() as tmpdir:
 
 	with TestWithTempCurrentDir():
 		os.chdir(tmpdir)
-		assert os.getcwd() == tmpdir
+		assert os.getcwd() == os.path.realpath(tmpdir)
 		os.path.exists(FILE_NAME)
 
 # supports
diff --git a/tests/snippets/sysmod.py b/tests/snippets/sysmod.py
index 23dd70f9b..adabb57d2 100644
--- a/tests/snippets/sysmod.py
+++ b/tests/snippets/sysmod.py
@@ -14,6 +14,8 @@ assert isinstance(sys.implementation.cache_tag, str)
 assert sys.getfilesystemencoding() == 'utf-8'
 assert sys.getfilesystemencodeerrors().startswith('surrogate')
 
+assert sys.byteorder == "little" or sys.byteorder == "big"
+
 assert isinstance(sys.flags, tuple)
 assert type(sys.flags).__name__ == "flags"
 assert type(sys.flags.optimize) is int
diff --git a/tests/snippets/test_struct.py b/tests/snippets/test_struct.py
index c13e713a1..8f535f63c 100644
--- a/tests/snippets/test_struct.py
+++ b/tests/snippets/test_struct.py
@@ -8,3 +8,17 @@ v1, v2 = struct.unpack('IH', data)
 assert v1 == 14
 assert v2 == 12
 
+data = struct.pack('<IH', 14, 12)
+assert data == bytes([14, 0, 0, 0, 12, 0])
+
+v1, v2 = struct.unpack('<IH', data)
+assert v1 == 14
+assert v2 == 12
+
+data = struct.pack('>IH', 14, 12)
+assert data == bytes([0, 0, 0, 14, 0, 12])
+
+v1, v2 = struct.unpack('>IH', data)
+assert v1 == 14
+assert v2 == 12
+
diff --git a/tests/snippets/testutils.py b/tests/snippets/testutils.py
index ea4dd9138..21662c461 100644
--- a/tests/snippets/testutils.py
+++ b/tests/snippets/testutils.py
@@ -23,6 +23,7 @@ def assert_raises(exc_type, expr, msg=None):
 class assertRaises:
     def __init__(self, expected):
         self.expected = expected
+        self.exception = None
 
     def __enter__(self):
         return self
@@ -33,6 +34,8 @@ class assertRaises:
             assert False, failmsg
         if not issubclass(exc_type, self.expected):
             return False
+
+        self.exception = exc_val
         return True
 
 
diff --git a/tests/snippets/tuple.py b/tests/snippets/tuple.py
index b7393fe00..86f12fe94 100644
--- a/tests/snippets/tuple.py
+++ b/tests/snippets/tuple.py
@@ -9,7 +9,7 @@ assert y[0] == 1
 assert x + y == (1, 2, 1)
 
 assert x * 3 == (1, 2, 1, 2, 1, 2)
-# assert 3 * x == (1, 2, 1, 2, 1, 2)
+assert 3 * x == (1, 2, 1, 2, 1, 2)
 assert x * 0 == ()
 assert x * -1 == ()  # integers less than zero treated as 0
 
diff --git a/vm/src/dictdatatype.rs b/vm/src/dictdatatype.rs
index ca20f2012..e52e83b8c 100644
--- a/vm/src/dictdatatype.rs
+++ b/vm/src/dictdatatype.rs
@@ -129,8 +129,7 @@ impl<T: Clone> Dict<T> {
         if self.delete_if_exists(vm, key)? {
             Ok(())
         } else {
-            let key_repr = vm.to_pystr(key)?;
-            Err(vm.new_key_error(format!("Key not found: {}", key_repr)))
+            Err(vm.new_key_error(key.clone()))
         }
     }
 
@@ -247,8 +246,7 @@ impl<T: Clone> Dict<T> {
             self.unchecked_delete(index);
             Ok(value)
         } else {
-            let key_repr = vm.to_pystr(key)?;
-            Err(vm.new_key_error(format!("Key not found: {}", key_repr)))
+            Err(vm.new_key_error(key.clone()))
         }
     }
 
diff --git a/vm/src/obj/objdict.rs b/vm/src/obj/objdict.rs
index 8d2e0fdff..7b708611e 100644
--- a/vm/src/obj/objdict.rs
+++ b/vm/src/obj/objdict.rs
@@ -210,7 +210,7 @@ impl PyDictRef {
             let method = method_or_err?;
             return vm.invoke(method, vec![key]);
         }
-        Err(vm.new_key_error(format!("Key not found: {}", vm.to_pystr(&key)?)))
+        Err(vm.new_key_error(key.clone()))
     }
 
     fn get(
@@ -266,7 +266,8 @@ impl PyDictRef {
         if let Some((key, value)) = entries.pop_front() {
             Ok(vm.ctx.new_tuple(vec![key, value]))
         } else {
-            Err(vm.new_key_error("popitem(): dictionary is empty".to_string()))
+            let err_msg = vm.new_str("popitem(): dictionary is empty".to_string());
+            Err(vm.new_key_error(err_msg))
         }
     }
 
diff --git a/vm/src/obj/objmappingproxy.rs b/vm/src/obj/objmappingproxy.rs
index c46591105..243a8c89c 100644
--- a/vm/src/obj/objmappingproxy.rs
+++ b/vm/src/obj/objmappingproxy.rs
@@ -28,7 +28,7 @@ impl PyMappingProxy {
         if let Some(value) = objtype::class_get_attr(&self.class, key.as_str()) {
             return Ok(value);
         }
-        Err(vm.new_key_error(format!("Key not found: {}", key)))
+        Err(vm.new_key_error(key.into_object()))
     }
 
     #[pymethod(name = "__contains__")]
diff --git a/vm/src/obj/objmemory.rs b/vm/src/obj/objmemory.rs
index 8c2af26f0..7e1628d13 100644
--- a/vm/src/obj/objmemory.rs
+++ b/vm/src/obj/objmemory.rs
@@ -33,6 +33,11 @@ impl PyMemoryView {
     fn obj(&self, __vm: &VirtualMachine) -> PyObjectRef {
         self.obj_ref.clone()
     }
+
+    #[pymethod(name = "__getitem__")]
+    fn getitem(&self, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult {
+        vm.call_method(&self.obj_ref, "__getitem__", vec![needle])
+    }
 }
 
 impl PyValue for PyMemoryView {
diff --git a/vm/src/obj/objset.rs b/vm/src/obj/objset.rs
index b7f0276ce..ede6029f3 100644
--- a/vm/src/obj/objset.rs
+++ b/vm/src/obj/objset.rs
@@ -269,7 +269,8 @@ impl PySetInner {
         if let Some((key, _)) = self.content.pop_front() {
             Ok(key)
         } else {
-            Err(vm.new_key_error("pop from an empty set".to_string()))
+            let err_msg = vm.new_str("pop from an empty set".to_string());
+            Err(vm.new_key_error(err_msg))
         }
     }
 
diff --git a/vm/src/obj/objstr.rs b/vm/src/obj/objstr.rs
index 1b6870e14..fafd23a65 100644
--- a/vm/src/obj/objstr.rs
+++ b/vm/src/obj/objstr.rs
@@ -1335,7 +1335,7 @@ fn perform_format(
                 let result = match arguments.get_optional_kwarg(&keyword) {
                     Some(argument) => call_object_format(vm, argument.clone(), &format_spec)?,
                     None => {
-                        return Err(vm.new_key_error(format!("'{}'", keyword)));
+                        return Err(vm.new_key_error(vm.new_str(keyword.to_string())));
                     }
                 };
                 get_value(&result)
diff --git a/vm/src/obj/objtuple.rs b/vm/src/obj/objtuple.rs
index b4f1699dd..a6e181f3b 100644
--- a/vm/src/obj/objtuple.rs
+++ b/vm/src/obj/objtuple.rs
@@ -168,6 +168,11 @@ impl PyTupleRef {
         vm.ctx.new_tuple(new_elements)
     }
 
+    fn rmul(self, counter: isize, vm: &VirtualMachine) -> PyObjectRef {
+        let new_elements = seq_mul(&self.elements, counter);
+        vm.ctx.new_tuple(new_elements)
+    }
+
     fn getitem(self, needle: PyObjectRef, vm: &VirtualMachine) -> PyResult {
         get_item(vm, self.as_object(), &self.elements, needle.clone())
     }
@@ -263,6 +268,7 @@ If the argument is a tuple, the return value is the same object.";
         "__len__" => context.new_rustfunc(PyTupleRef::len),
         "__new__" => context.new_rustfunc(tuple_new),
         "__mul__" => context.new_rustfunc(PyTupleRef::mul),
+        "__rmul__" => context.new_rustfunc(PyTupleRef::rmul),
         "__repr__" => context.new_rustfunc(PyTupleRef::repr),
         "count" => context.new_rustfunc(PyTupleRef::count),
         "__lt__" => context.new_rustfunc(PyTupleRef::lt),
diff --git a/vm/src/stdlib/imp.rs b/vm/src/stdlib/imp.rs
index 184fc5003..4c0f023d9 100644
--- a/vm/src/stdlib/imp.rs
+++ b/vm/src/stdlib/imp.rs
@@ -77,6 +77,10 @@ fn imp_is_frozen_package(_name: PyStringRef, _vm: &VirtualMachine) -> bool {
     false
 }
 
+fn imp_fix_co_filename(_code: PyObjectRef, _path: PyStringRef, _vm: &VirtualMachine) {
+    // TODO:
+}
+
 pub fn make_module(vm: &VirtualMachine) -> PyObjectRef {
     let ctx = &vm.ctx;
     let module = py_module!(vm, "_imp", {
@@ -91,6 +95,7 @@ pub fn make_module(vm: &VirtualMachine) -> PyObjectRef {
         "get_frozen_object" => ctx.new_rustfunc(imp_get_frozen_object),
         "init_frozen" => ctx.new_rustfunc(imp_init_frozen),
         "is_frozen_package" => ctx.new_rustfunc(imp_is_frozen_package),
+        "_fix_co_filename" => ctx.new_rustfunc(imp_fix_co_filename),
     });
 
     module
diff --git a/vm/src/stdlib/io.rs b/vm/src/stdlib/io.rs
index 783e9b96f..2d0b2286c 100644
--- a/vm/src/stdlib/io.rs
+++ b/vm/src/stdlib/io.rs
@@ -2,9 +2,7 @@
  * I/O core tools.
  */
 use std::cell::RefCell;
-use std::fs::File;
 use std::io::prelude::*;
-use std::io::BufReader;
 use std::io::Cursor;
 use std::io::SeekFrom;
 
@@ -18,9 +16,12 @@ use crate::function::{OptionalArg, PyFuncArgs};
 use crate::import;
 use crate::obj::objbytearray::PyByteArray;
 use crate::obj::objbytes;
+use crate::obj::objbytes::PyBytes;
 use crate::obj::objint;
 use crate::obj::objstr;
+use crate::obj::objtype;
 use crate::obj::objtype::PyClassRef;
+use crate::pyobject::TypeProtocol;
 use crate::pyobject::{BufferProtocol, PyObjectRef, PyRef, PyResult, PyValue};
 use crate::vm::VirtualMachine;
 
@@ -284,16 +285,19 @@ fn buffered_reader_read(vm: &VirtualMachine, args: PyFuncArgs) -> PyResult {
 }
 
 fn compute_c_flag(mode: &str) -> u32 {
-    let flags = match mode {
-        "w" => os::FileCreationFlags::O_WRONLY | os::FileCreationFlags::O_CREAT,
-        "x" => {
-            os::FileCreationFlags::O_WRONLY
-                | os::FileCreationFlags::O_CREAT
-                | os::FileCreationFlags::O_EXCL
-        }
-        "a" => os::FileCreationFlags::O_APPEND,
-        "+" => os::FileCreationFlags::O_RDWR,
-        _ => os::FileCreationFlags::O_RDONLY,
+    let flags = match mode.chars().next() {
+        Some(mode) => match mode {
+            'w' => os::FileCreationFlags::O_WRONLY | os::FileCreationFlags::O_CREAT,
+            'x' => {
+                os::FileCreationFlags::O_WRONLY
+                    | os::FileCreationFlags::O_CREAT
+                    | os::FileCreationFlags::O_EXCL
+            }
+            'a' => os::FileCreationFlags::O_APPEND,
+            '+' => os::FileCreationFlags::O_RDWR,
+            _ => os::FileCreationFlags::O_RDONLY,
+        },
+        None => os::FileCreationFlags::O_RDONLY,
     };
     flags.bits()
 }
@@ -302,47 +306,43 @@ fn file_io_init(vm: &VirtualMachine, args: PyFuncArgs) -> PyResult {
     arg_check!(
         vm,
         args,
-        required = [(file_io, None), (name, Some(vm.ctx.str_type()))],
+        required = [(file_io, None), (name, None)],
         optional = [(mode, Some(vm.ctx.str_type()))]
     );
 
-    let rust_mode = mode.map_or("r".to_string(), objstr::get_value);
+    let file_no = if objtype::isinstance(&name, &vm.ctx.str_type()) {
+        let rust_mode = mode.map_or("r".to_string(), objstr::get_value);
+        let args = vec![
+            name.clone(),
+            vm.ctx
+                .new_int(compute_c_flag(&rust_mode).to_bigint().unwrap()),
+        ];
+        os::os_open(vm, PyFuncArgs::new(args, vec![]))?
+    } else if objtype::isinstance(&name, &vm.ctx.int_type()) {
+        name.clone()
+    } else {
+        return Err(vm.new_type_error("name parameter must be string or int".to_string()));
+    };
 
-    match compute_c_flag(&rust_mode).to_bigint() {
-        Some(os_mode) => {
-            let args = vec![name.clone(), vm.ctx.new_int(os_mode)];
-            let file_no = os::os_open(vm, PyFuncArgs::new(args, vec![]))?;
-
-            vm.set_attr(file_io, "name", name.clone())?;
-            vm.set_attr(file_io, "fileno", file_no)?;
-            vm.set_attr(file_io, "closefd", vm.new_bool(false))?;
-            vm.set_attr(file_io, "closed", vm.new_bool(false))?;
-
-            Ok(vm.get_none())
-        }
-        None => Err(vm.new_type_error(format!("invalid mode {}", rust_mode))),
-    }
+    vm.set_attr(file_io, "name", name.clone())?;
+    vm.set_attr(file_io, "fileno", file_no)?;
+    vm.set_attr(file_io, "closefd", vm.new_bool(false))?;
+    vm.set_attr(file_io, "closed", vm.new_bool(false))?;
+    Ok(vm.get_none())
 }
 
 fn file_io_read(vm: &VirtualMachine, args: PyFuncArgs) -> PyResult {
     arg_check!(vm, args, required = [(file_io, None)]);
-    let py_name = vm.get_attribute(file_io.clone(), "name")?;
-    let f = match File::open(objstr::get_value(&py_name)) {
-        Ok(v) => Ok(v),
-        Err(_) => Err(vm.new_type_error("Error opening file".to_string())),
-    };
 
-    let buffer = match f {
-        Ok(v) => Ok(BufReader::new(v)),
-        Err(_) => Err(vm.new_type_error("Error reading from file".to_string())),
-    };
+    let file_no = vm.get_attribute(file_io.clone(), "fileno")?;
+    let raw_fd = objint::get_value(&file_no).to_i64().unwrap();
+
+    let mut handle = os::rust_file(raw_fd);
 
     let mut bytes = vec![];
-    if let Ok(mut buff) = buffer {
-        match buff.read_to_end(&mut bytes) {
-            Ok(_) => {}
-            Err(_) => return Err(vm.new_value_error("Error reading from Buffer".to_string())),
-        }
+    match handle.read_to_end(&mut bytes) {
+        Ok(_) => {}
+        Err(_) => return Err(vm.new_value_error("Error reading from Buffer".to_string())),
     }
 
     Ok(vm.ctx.new_bytes(bytes))
@@ -385,11 +385,7 @@ fn file_io_readinto(vm: &VirtualMachine, args: PyFuncArgs) -> PyResult {
 }
 
 fn file_io_write(vm: &VirtualMachine, args: PyFuncArgs) -> PyResult {
-    arg_check!(
-        vm,
-        args,
-        required = [(file_io, None), (obj, Some(vm.ctx.bytes_type()))]
-    );
+    arg_check!(vm, args, required = [(file_io, None), (obj, None)]);
 
     let file_no = vm.get_attribute(file_io.clone(), "fileno")?;
     let raw_fd = objint::get_value(&file_no).to_i64().unwrap();
@@ -399,22 +395,25 @@ fn file_io_write(vm: &VirtualMachine, args: PyFuncArgs) -> PyResult {
     //to support windows - i.e. raw file_handles
     let mut handle = os::rust_file(raw_fd);
 
-    match obj.payload::<PyByteArray>() {
-        Some(bytes) => {
-            let value_mut = &mut bytes.inner.borrow_mut().elements;
-            match handle.write(&value_mut[..]) {
-                Ok(len) => {
-                    //reset raw fd on the FileIO object
-                    let updated = os::raw_file_number(handle);
-                    vm.set_attr(file_io, "fileno", vm.ctx.new_int(updated))?;
+    let bytes = match_class!(obj.clone(),
+        i @ PyBytes => Ok(i.get_value().to_vec()),
+        j @ PyByteArray => Ok(j.inner.borrow().elements.to_vec()),
+        obj => Err(vm.new_type_error(format!(
+                    "a bytes-like object is required, not {}",
+                    obj.class()
+                )))
+    );
 
-                    //return number of bytes written
-                    Ok(vm.ctx.new_int(len))
-                }
-                Err(_) => Err(vm.new_value_error("Error Writing Bytes to Handle".to_string())),
-            }
+    match handle.write(&bytes?) {
+        Ok(len) => {
+            //reset raw fd on the FileIO object
+            let updated = os::raw_file_number(handle);
+            vm.set_attr(file_io, "fileno", vm.ctx.new_int(updated))?;
+
+            //return number of bytes written
+            Ok(vm.ctx.new_int(len))
         }
-        None => Err(vm.new_value_error("Expected Bytes Object".to_string())),
+        Err(_) => Err(vm.new_value_error("Error Writing Bytes to Handle".to_string())),
     }
 }
 
diff --git a/vm/src/stdlib/os.rs b/vm/src/stdlib/os.rs
index 24a7a6741..11f6c1676 100644
--- a/vm/src/stdlib/os.rs
+++ b/vm/src/stdlib/os.rs
@@ -605,6 +605,17 @@ fn os_stat(path: PyStringRef, vm: &VirtualMachine) -> PyResult {
     unimplemented!();
 }
 
+fn os_lstat(path: PyStringRef, dir_fd: DirFd, vm: &VirtualMachine) -> PyResult<StatResult> {
+    os_stat(
+        path,
+        dir_fd,
+        FollowSymlinks {
+            follow_symlinks: false,
+        },
+        vm,
+    )
+}
+
 #[cfg(unix)]
 fn os_symlink(
     src: PyStringRef,
@@ -788,6 +799,7 @@ pub fn make_module(vm: &VirtualMachine) -> PyObjectRef {
         "ScandirIter" => scandir_iter,
         "DirEntry" => dir_entry,
         "stat_result" => stat_result,
+        "lstat" => ctx.new_rustfunc(os_lstat),
         "getcwd" => ctx.new_rustfunc(os_getcwd),
         "chdir" => ctx.new_rustfunc(os_chdir),
         "fspath" => ctx.new_rustfunc(os_fspath),
diff --git a/vm/src/stdlib/pwd.rs b/vm/src/stdlib/pwd.rs
index 1f5092540..85cb2d3eb 100644
--- a/vm/src/stdlib/pwd.rs
+++ b/vm/src/stdlib/pwd.rs
@@ -48,7 +48,7 @@ fn pwd_getpwnam(name: PyStringRef, vm: &VirtualMachine) -> PyResult<Passwd> {
         Ok(Some(passwd)) => Ok(passwd),
         _ => {
             let name_repr = vm.to_repr(name.as_object())?;
-            let message = format!("getpwnam(): name not found: {}", name_repr);
+            let message = vm.new_str(format!("getpwnam(): name not found: {}", name_repr));
             Err(vm.new_key_error(message))
         }
     }
@@ -58,7 +58,7 @@ fn pwd_getpwuid(uid: u32, vm: &VirtualMachine) -> PyResult<Passwd> {
     match Passwd::from_uid(uid) {
         Some(passwd) => Ok(passwd),
         _ => {
-            let message = format!("getpwuid(): uid not found: {}", uid);
+            let message = vm.new_str(format!("getpwuid(): uid not found: {}", uid));
             Err(vm.new_key_error(message))
         }
     }
diff --git a/vm/src/stdlib/pystruct.rs b/vm/src/stdlib/pystruct.rs
index 4a454b0c9..09f007e60 100644
--- a/vm/src/stdlib/pystruct.rs
+++ b/vm/src/stdlib/pystruct.rs
@@ -1,6 +1,8 @@
 /*
  * Python struct module.
  *
+ * Docs: https://docs.python.org/3/library/struct.html
+ *
  * renamed to pystruct since struct is a rust keyword.
  *
  * Use this rust module to do byte packing:
@@ -8,8 +10,9 @@
  */
 
 use std::io::{Cursor, Read, Write};
+use std::iter::Peekable;
 
-use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
+use byteorder::{ReadBytesExt, WriteBytesExt};
 use num_bigint::BigInt;
 use num_traits::ToPrimitive;
 
@@ -19,28 +22,86 @@ use crate::pyobject::{PyObjectRef, PyResult};
 use crate::VirtualMachine;
 
 #[derive(Debug)]
-struct FormatCode {
-    code: char,
-    repeat: i32,
+struct FormatSpec {
+    endianness: Endianness,
+    codes: Vec<FormatCode>,
 }
 
-fn parse_format_string(fmt: String) -> Vec<FormatCode> {
+#[derive(Debug)]
+enum Endianness {
+    Native,
+    Little,
+    Big,
+    Network,
+}
+
+#[derive(Debug)]
+struct FormatCode {
+    code: char,
+}
+
+fn parse_format_string(fmt: String) -> Result<FormatSpec, String> {
+    let mut chars = fmt.chars().peekable();
+
     // First determine "<", ">","!" or "="
-    // TODO
+    let endianness = parse_endiannes(&mut chars);
 
     // Now, analyze struct string furter:
+    let codes = parse_format_codes(&mut chars)?;
+
+    Ok(FormatSpec { endianness, codes })
+}
+
+/// Parse endianness
+/// See also: https://docs.python.org/3/library/struct.html?highlight=struct#byte-order-size-and-alignment
+fn parse_endiannes<I>(chars: &mut Peekable<I>) -> Endianness
+where
+    I: Sized,
+    I: Iterator<Item = char>,
+{
+    match chars.peek() {
+        Some('@') => {
+            chars.next().unwrap();
+            Endianness::Native
+        }
+        Some('=') => {
+            chars.next().unwrap();
+            Endianness::Native
+        }
+        Some('<') => {
+            chars.next().unwrap();
+            Endianness::Little
+        }
+        Some('>') => {
+            chars.next().unwrap();
+            Endianness::Big
+        }
+        Some('!') => {
+            chars.next().unwrap();
+            Endianness::Network
+        }
+        _ => Endianness::Native,
+    }
+}
+
+fn parse_format_codes<I>(chars: &mut Peekable<I>) -> Result<Vec<FormatCode>, String>
+where
+    I: Sized,
+    I: Iterator<Item = char>,
+{
     let mut codes = vec![];
-    for c in fmt.chars() {
+    for c in chars {
         match c {
-            'b' | 'B' | 'h' | 'H' | 'i' | 'I' | 'q' | 'Q' | 'f' | 'd' => {
-                codes.push(FormatCode { code: c, repeat: 1 })
+            'b' | 'B' | 'h' | 'H' | 'i' | 'I' | 'l' | 'L' | 'q' | 'Q' | 'f' | 'd' => {
+                codes.push(FormatCode { code: c })
             }
             c => {
-                panic!("Illegal format code {:?}", c);
+                return Err(format!("Illegal format code {:?}", c));
             }
         }
     }
-    codes
+
+    Ok(codes)
 }
 
 fn get_int(vm: &VirtualMachine, arg: &PyObjectRef) -> PyResult<BigInt> {
@@ -69,60 +130,112 @@ fn pack_bool(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResu
     }
 }
 
-fn pack_i16(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()> {
+fn pack_i16<Endianness>(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()>
+where
+    Endianness: byteorder::ByteOrder,
+{
     let v = get_int(vm, arg)?.to_i16().unwrap();
-    data.write_i16::<LittleEndian>(v).unwrap();
+    data.write_i16::<Endianness>(v).unwrap();
     Ok(())
 }
 
-fn pack_u16(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()> {
+fn pack_u16<Endianness>(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()>
+where
+    Endianness: byteorder::ByteOrder,
+{
     let v = get_int(vm, arg)?.to_u16().unwrap();
-    data.write_u16::<LittleEndian>(v).unwrap();
+    data.write_u16::<Endianness>(v).unwrap();
     Ok(())
 }
 
-fn pack_i32(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()> {
+fn pack_i32<Endianness>(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()>
+where
+    Endianness: byteorder::ByteOrder,
+{
     let v = get_int(vm, arg)?.to_i32().unwrap();
-    data.write_i32::<LittleEndian>(v).unwrap();
+    data.write_i32::<Endianness>(v).unwrap();
     Ok(())
 }
 
-fn pack_u32(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()> {
+fn pack_u32<Endianness>(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()>
+where
+    Endianness: byteorder::ByteOrder,
+{
     let v = get_int(vm, arg)?.to_u32().unwrap();
-    data.write_u32::<LittleEndian>(v).unwrap();
+    data.write_u32::<Endianness>(v).unwrap();
     Ok(())
 }
 
-fn pack_i64(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()> {
+fn pack_i64<Endianness>(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()>
+where
+    Endianness: byteorder::ByteOrder,
+{
     let v = get_int(vm, arg)?.to_i64().unwrap();
-    data.write_i64::<LittleEndian>(v).unwrap();
+    data.write_i64::<Endianness>(v).unwrap();
     Ok(())
 }
 
-fn pack_u64(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()> {
+fn pack_u64<Endianness>(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()>
+where
+    Endianness: byteorder::ByteOrder,
+{
     let v = get_int(vm, arg)?.to_u64().unwrap();
-    data.write_u64::<LittleEndian>(v).unwrap();
+    data.write_u64::<Endianness>(v).unwrap();
     Ok(())
 }
 
-fn pack_f32(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()> {
+fn pack_f32<Endianness>(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()>
+where
+    Endianness: byteorder::ByteOrder,
+{
+    let v = get_float(vm, arg)? as f32;
+    data.write_f32::<Endianness>(v).unwrap();
+    Ok(())
+}
+
+fn pack_f64<Endianness>(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()>
+where
+    Endianness: byteorder::ByteOrder,
+{
+    let v = get_float(vm, arg)?;
+    data.write_f64::<Endianness>(v).unwrap();
+    Ok(())
+}
+
+fn get_float(vm: &VirtualMachine, arg: &PyObjectRef) -> PyResult<f64> {
     if objtype::isinstance(&arg, &vm.ctx.float_type()) {
-        let v = objfloat::get_value(arg) as f32;
-        data.write_f32::<LittleEndian>(v).unwrap();
-        Ok(())
+        Ok(objfloat::get_value(arg))
     } else {
         Err(vm.new_type_error("Expected float".to_string()))
     }
 }
 
-fn pack_f64(vm: &VirtualMachine, arg: &PyObjectRef, data: &mut Write) -> PyResult<()> {
-    if objtype::isinstance(&arg, &vm.ctx.float_type()) {
-        let v = objfloat::get_value(arg) as f64;
-        data.write_f64::<LittleEndian>(v).unwrap();
-        Ok(())
-    } else {
-        Err(vm.new_type_error("Expected float".to_string()))
+fn pack_item<Endianness>(
+    vm: &VirtualMachine,
+    code: &FormatCode,
+    arg: &PyObjectRef,
+    data: &mut Write,
+) -> PyResult<()>
+where
+    Endianness: byteorder::ByteOrder,
+{
+    match code.code {
+        'b' => pack_i8(vm, arg, data)?,
+        'B' => pack_u8(vm, arg, data)?,
+        '?' => pack_bool(vm, arg, data)?,
+        'h' => pack_i16::<Endianness>(vm, arg, data)?,
+        'H' => pack_u16::<Endianness>(vm, arg, data)?,
+        'i' | 'l' => pack_i32::<Endianness>(vm, arg, data)?,
+        'I' | 'L' => pack_u32::<Endianness>(vm, arg, data)?,
+        'q' => pack_i64::<Endianness>(vm, arg, data)?,
+        'Q' => pack_u64::<Endianness>(vm, arg, data)?,
+        'f' => pack_f32::<Endianness>(vm, arg, data)?,
+        'd' => pack_f64::<Endianness>(vm, arg, data)?,
+        c => {
+            panic!("Unsupported format code {:?}", c);
+        }
     }
+    Ok(())
 }
 
 fn struct_pack(vm: &VirtualMachine, args: PyFuncArgs) -> PyResult {
@@ -136,30 +249,26 @@ fn struct_pack(vm: &VirtualMachine, args: PyFuncArgs) -> PyResult {
         if objtype::isinstance(&fmt_arg, &vm.ctx.str_type()) {
             let fmt_str = objstr::get_value(&fmt_arg);
 
-            let codes = parse_format_string(fmt_str);
+            let format_spec = parse_format_string(fmt_str).map_err(|e| vm.new_value_error(e))?;;
 
-            if codes.len() + 1 == args.args.len() {
+            if format_spec.codes.len() + 1 == args.args.len() {
                 // Create data vector:
                 let mut data = Vec::<u8>::new();
                 // Loop over all opcodes:
-                for (code, arg) in codes.iter().zip(args.args.iter().skip(1)) {
+                for (code, arg) in format_spec.codes.iter().zip(args.args.iter().skip(1)) {
                     debug!("code: {:?}", code);
-                    match code.code {
-                        'b' => pack_i8(vm, arg, &mut data)?,
-                        'B' => pack_u8(vm, arg, &mut data)?,
-                        '?' => pack_bool(vm, arg, &mut data)?,
-                        'h' => pack_i16(vm, arg, &mut data)?,
-                        'H' => pack_u16(vm, arg, &mut data)?,
-                        'i' => pack_i32(vm, arg, &mut data)?,
-                        'I' => pack_u32(vm, arg, &mut data)?,
-                        'l' => pack_i32(vm, arg, &mut data)?,
-                        'L' => pack_u32(vm, arg, &mut data)?,
-                        'q' => pack_i64(vm, arg, &mut data)?,
-                        'Q' => pack_u64(vm, arg, &mut data)?,
-                        'f' => pack_f32(vm, arg, &mut data)?,
-                        'd' => pack_f64(vm, arg, &mut data)?,
-                        c => {
-                            panic!("Unsupported format code {:?}", c);
+                    match format_spec.endianness {
+                        Endianness::Little => {
+                            pack_item::<byteorder::LittleEndian>(vm, code, arg, &mut data)?
+                        }
+                        Endianness::Big => {
+                            pack_item::<byteorder::BigEndian>(vm, code, arg, &mut data)?
+                        }
+                        Endianness::Network => {
+                            pack_item::<byteorder::NetworkEndian>(vm, code, arg, &mut data)?
+                        }
+                        Endianness::Native => {
+                            pack_item::<byteorder::NativeEndian>(vm, code, arg, &mut data)?
                         }
                     }
                 }
@@ -168,7 +277,7 @@ fn struct_pack(vm: &VirtualMachine, args: PyFuncArgs) -> PyResult {
             } else {
                 Err(vm.new_type_error(format!(
                     "Expected {} arguments (got: {})",
-                    codes.len() + 1,
+                    format_spec.codes.len() + 1,
                     args.args.len()
                 )))
             }
@@ -199,57 +308,81 @@ fn unpack_bool(vm: &VirtualMachine, rdr: &mut Read) -> PyResult {
     }
 }
 
-fn unpack_i16(vm: &VirtualMachine, rdr: &mut Read) -> PyResult {
-    match rdr.read_i16::<LittleEndian>() {
+fn unpack_i16<Endianness>(vm: &VirtualMachine, rdr: &mut Read) -> PyResult
+where
+    Endianness: byteorder::ByteOrder,
+{
+    match rdr.read_i16::<Endianness>() {
         Err(err) => panic!("Error in reading {:?}", err),
         Ok(v) => Ok(vm.ctx.new_int(v)),
     }
 }
 
-fn unpack_u16(vm: &VirtualMachine, rdr: &mut Read) -> PyResult {
-    match rdr.read_u16::<LittleEndian>() {
+fn unpack_u16<Endianness>(vm: &VirtualMachine, rdr: &mut Read) -> PyResult
+where
+    Endianness: byteorder::ByteOrder,
+{
+    match rdr.read_u16::<Endianness>() {
         Err(err) => panic!("Error in reading {:?}", err),
         Ok(v) => Ok(vm.ctx.new_int(v)),
     }
 }
 
-fn unpack_i32(vm: &VirtualMachine, rdr: &mut Read) -> PyResult {
-    match rdr.read_i32::<LittleEndian>() {
+fn unpack_i32<Endianness>(vm: &VirtualMachine, rdr: &mut Read) -> PyResult
+where
+    Endianness: byteorder::ByteOrder,
+{
+    match rdr.read_i32::<Endianness>() {
         Err(err) => panic!("Error in reading {:?}", err),
         Ok(v) => Ok(vm.ctx.new_int(v)),
     }
 }
 
-fn unpack_u32(vm: &VirtualMachine, rdr: &mut Read) -> PyResult {
-    match rdr.read_u32::<LittleEndian>() {
+fn unpack_u32<Endianness>(vm: &VirtualMachine, rdr: &mut Read) -> PyResult
+where
+    Endianness: byteorder::ByteOrder,
+{
+    match rdr.read_u32::<Endianness>() {
         Err(err) => panic!("Error in reading {:?}", err),
         Ok(v) => Ok(vm.ctx.new_int(v)),
     }
 }
 
-fn unpack_i64(vm: &VirtualMachine, rdr: &mut Read) -> PyResult {
-    match rdr.read_i64::<LittleEndian>() {
+fn unpack_i64<Endianness>(vm: &VirtualMachine, rdr: &mut Read) -> PyResult
+where
+    Endianness: byteorder::ByteOrder,
+{
+    match rdr.read_i64::<Endianness>() {
         Err(err) => panic!("Error in reading {:?}", err),
         Ok(v) => Ok(vm.ctx.new_int(v)),
     }
 }
 
-fn unpack_u64(vm: &VirtualMachine, rdr: &mut Read) -> PyResult {
-    match rdr.read_u64::<LittleEndian>() {
+fn unpack_u64<Endianness>(vm: &VirtualMachine, rdr: &mut Read) -> PyResult
+where
+    Endianness: byteorder::ByteOrder,
+{
+    match rdr.read_u64::<Endianness>() {
         Err(err) => panic!("Error in reading {:?}", err),
         Ok(v) => Ok(vm.ctx.new_int(v)),
     }
 }
 
-fn unpack_f32(vm: &VirtualMachine, rdr: &mut Read) -> PyResult {
-    match rdr.read_f32::<LittleEndian>() {
+fn unpack_f32<Endianness>(vm: &VirtualMachine, rdr: &mut Read) -> PyResult
+where
+    Endianness: byteorder::ByteOrder,
+{
+    match rdr.read_f32::<Endianness>() {
         Err(err) => panic!("Error in reading {:?}", err),
         Ok(v) => Ok(vm.ctx.new_float(f64::from(v))),
     }
 }
 
-fn unpack_f64(vm: &VirtualMachine, rdr: &mut Read) -> PyResult {
-    match rdr.read_f64::<LittleEndian>() {
+fn unpack_f64<Endianness>(vm: &VirtualMachine, rdr: &mut Read) -> PyResult
+where
+    Endianness: byteorder::ByteOrder,
+{
+    match rdr.read_f64::<Endianness>() {
         Err(err) => panic!("Error in reading {:?}", err),
         Ok(v) => Ok(vm.ctx.new_float(v)),
     }
@@ -267,41 +400,55 @@ fn struct_unpack(vm: &VirtualMachine, args: PyFuncArgs) -> PyResult {
 
     let fmt_str = objstr::get_value(&fmt);
 
-    let codes = parse_format_string(fmt_str);
+    let format_spec = parse_format_string(fmt_str).map_err(|e| vm.new_value_error(e))?;
     let data = objbytes::get_value(buffer).to_vec();
     let mut rdr = Cursor::new(data);
 
     let mut items = vec![];
-    for code in codes {
+    for code in format_spec.codes {
         debug!("unpack code: {:?}", code);
-        match code.code {
-            'b' => items.push(unpack_i8(vm, &mut rdr)?),
-            'B' => items.push(unpack_u8(vm, &mut rdr)?),
-            '?' => items.push(unpack_bool(vm, &mut rdr)?),
-            'h' => items.push(unpack_i16(vm, &mut rdr)?),
-            'H' => items.push(unpack_u16(vm, &mut rdr)?),
-            'i' => items.push(unpack_i32(vm, &mut rdr)?),
-            'I' => items.push(unpack_u32(vm, &mut rdr)?),
-            'l' => items.push(unpack_i32(vm, &mut rdr)?),
-            'L' => items.push(unpack_u32(vm, &mut rdr)?),
-            'q' => items.push(unpack_i64(vm, &mut rdr)?),
-            'Q' => items.push(unpack_u64(vm, &mut rdr)?),
-            'f' => items.push(unpack_f32(vm, &mut rdr)?),
-            'd' => items.push(unpack_f64(vm, &mut rdr)?),
-            c => {
-                panic!("Unsupported format code {:?}", c);
-            }
-        }
+        let item = match format_spec.endianness {
+            Endianness::Little => unpack_code::<byteorder::LittleEndian>(vm, &code, &mut rdr)?,
+            Endianness::Big => unpack_code::<byteorder::BigEndian>(vm, &code, &mut rdr)?,
+            Endianness::Network => unpack_code::<byteorder::NetworkEndian>(vm, &code, &mut rdr)?,
+            Endianness::Native => unpack_code::<byteorder::NativeEndian>(vm, &code, &mut rdr)?,
+        };
+        items.push(item);
     }
 
     Ok(vm.ctx.new_tuple(items))
 }
 
+fn unpack_code<Endianness>(vm: &VirtualMachine, code: &FormatCode, rdr: &mut Read) -> PyResult
+where
+    Endianness: byteorder::ByteOrder,
+{
+    match code.code {
+        'b' => unpack_i8(vm, rdr),
+        'B' => unpack_u8(vm, rdr),
+        '?' => unpack_bool(vm, rdr),
+        'h' => unpack_i16::<Endianness>(vm, rdr),
+        'H' => unpack_u16::<Endianness>(vm, rdr),
+        'i' | 'l' => unpack_i32::<Endianness>(vm, rdr),
+        'I' | 'L' => unpack_u32::<Endianness>(vm, rdr),
+        'q' => unpack_i64::<Endianness>(vm, rdr),
+        'Q' => unpack_u64::<Endianness>(vm, rdr),
+        'f' => unpack_f32::<Endianness>(vm, rdr),
+        'd' => unpack_f64::<Endianness>(vm, rdr),
+        c => {
+            panic!("Unsupported format code {:?}", c);
+        }
+    }
+}
+
 pub fn make_module(vm: &VirtualMachine) -> PyObjectRef {
     let ctx = &vm.ctx;
 
+    let struct_error = ctx.new_class("struct.error", ctx.object());
+
     py_module!(vm, "struct", {
         "pack" => ctx.new_rustfunc(struct_pack),
-        "unpack" => ctx.new_rustfunc(struct_unpack)
+        "unpack" => ctx.new_rustfunc(struct_unpack),
+        "error" => struct_error,
     })
 }
diff --git a/vm/src/sysmodule.rs b/vm/src/sysmodule.rs
index b81b8db52..c20f7b167 100644
--- a/vm/src/sysmodule.rs
+++ b/vm/src/sysmodule.rs
@@ -151,6 +151,15 @@ pub fn make_module(vm: &VirtualMachine, module: PyObjectRef, builtins: PyObjectR
         "unknown".to_string()
     };
 
+    // https://doc.rust-lang.org/reference/conditional-compilation.html#target_endian
+    let bytorder = if cfg!(target_endian = "little") {
+        "little".to_string()
+    } else if cfg!(target_endian = "big") {
+        "big".to_string()
+    } else {
+        "unknown".to_string()
+    };
+
     let sys_doc = "This module provides access to some objects used or maintained by the
 interpreter and to functions that interact strongly with the interpreter.
 
@@ -229,6 +238,7 @@ settrace() -- set the global debug tracing function
       "__name__" => ctx.new_str(String::from("sys")),
       "argv" => argv(ctx),
       "builtin_module_names" => ctx.new_tuple(module_names.iter().map(|v| v.into_pyobject(vm).unwrap()).collect()),
+      "byteorder" => ctx.new_str(bytorder),
       "flags" => flags,
       "getrefcount" => ctx.new_rustfunc(sys_getrefcount),
       "getsizeof" => ctx.new_rustfunc(sys_getsizeof),
diff --git a/vm/src/vm.rs b/vm/src/vm.rs
index 8656c7dd4..a1c7e5868 100644
--- a/vm/src/vm.rs
+++ b/vm/src/vm.rs
@@ -167,20 +167,20 @@ impl VirtualMachine {
         self.ctx.new_bool(b)
     }
 
-    pub fn new_empty_exception(&self, exc_type: PyClassRef) -> PyResult {
+    fn new_exception_obj(&self, exc_type: PyClassRef, args: Vec<PyObjectRef>) -> PyResult {
+        // TODO: add repr of args into logging?
         info!("New exception created: {}", exc_type.name);
-        let args = PyFuncArgs::default();
         self.invoke(exc_type.into_object(), args)
     }
 
+    pub fn new_empty_exception(&self, exc_type: PyClassRef) -> PyResult {
+        self.new_exception_obj(exc_type, vec![])
+    }
+
     /// Create Python instance of `exc_type` with message as first element of `args` tuple
     pub fn new_exception(&self, exc_type: PyClassRef, msg: String) -> PyObjectRef {
-        // TODO: exc_type may be user-defined exception, so we should return PyResult
-        // TODO: maybe there is a clearer way to create an instance:
-        info!("New exception created: {}('{}')", exc_type.name, msg);
-        let pymsg = self.new_str(msg);
-        let args: Vec<PyObjectRef> = vec![pymsg];
-        self.invoke(exc_type.into_object(), args).unwrap()
+        let pystr_msg = self.new_str(msg);
+        self.new_exception_obj(exc_type, vec![pystr_msg]).unwrap()
     }
 
     pub fn new_attribute_error(&self, msg: String) -> PyObjectRef {
@@ -224,9 +224,9 @@ impl VirtualMachine {
         self.new_exception(value_error, msg)
     }
 
-    pub fn new_key_error(&self, msg: String) -> PyObjectRef {
+    pub fn new_key_error(&self, obj: PyObjectRef) -> PyObjectRef {
         let key_error = self.ctx.exceptions.key_error.clone();
-        self.new_exception(key_error, msg)
+        self.new_exception_obj(key_error, vec![obj]).unwrap()
     }
 
     pub fn new_index_error(&self, msg: String) -> PyObjectRef {