diff --git a/pyproject.toml b/pyproject.toml
index 21d506f1..4b4c1a41 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -94,7 +94,9 @@ ignore = [
   'PLR0915',  # Too many statements
   'PLR2004',  # Magic value used in comparison
   'RUF005',  # Consider iterable unpacking instead of concatenation
-  'RUF012'  # Mutable class attributes should be annotated with `typing.ClassVar`
+  'RUF012',  # Mutable class attributes should be annotated with `typing.ClassVar`
+  'PLC0415',  # `import` should be at the top-level of a file
+  'N801',  # Class name should use CapWords convention (for internal __NULL sentinel)
 ]
 select = [
   'E',  # pydocstyle
diff --git a/src/plumpy/base/state_machine.py b/src/plumpy/base/state_machine.py
index 317d73bb..ea5f93fd 100644
--- a/src/plumpy/base/state_machine.py
+++ b/src/plumpy/base/state_machine.py
@@ -114,7 +114,7 @@ def transition(self: Any, *a: Any, **kw: Any) -> Any:
 
                     raise EventError(
                         evt_label,
-                        'Event produced invalid state transition from ' f'{initial.LABEL} to {self._state.LABEL}',
+                        f'Event produced invalid state transition from {initial.LABEL} to {self._state.LABEL}',
                     )
 
             return result
diff --git a/src/plumpy/lang.py b/src/plumpy/lang.py
index 4efd5827..1aa91e3a 100644
--- a/src/plumpy/lang.py
+++ b/src/plumpy/lang.py
@@ -13,7 +13,7 @@ def wrap(func: Callable[..., Any]) -> Callable[..., Any]:
         if isinstance(func, property):
             raise RuntimeError('Protected must go after @property decorator')
 
-        args = inspect.getargspec(func)[0]
+        args = inspect.getfullargspec(func)[0]
         if len(args) == 0:
             raise RuntimeError('Can only use the protected decorator on member functions')
 
@@ -45,7 +45,7 @@ def wrap(func: Callable[..., Any]) -> Callable[..., Any]:
         if isinstance(func, property):
             raise RuntimeError('Override must go after @property decorator')
 
-        args = inspect.getargspec(func)[0]
+        args = inspect.getfullargspec(func)[0]
         if len(args) == 0:
             raise RuntimeError('Can only use the override decorator on member functions')
 
@@ -67,9 +67,12 @@ def wrapped_fn(self: Any, *args: Any, **kwargs: Any) -> Callable[..., Any]:
     return wrap
 
 
-class __NULL:  # noqa: N801
+class __NULL:
     def __eq__(self, other: Any) -> bool:
         return isinstance(other, self.__class__)
 
+    def __hash__(self) -> int:
+        return id(self)
+
 
 NULL = __NULL()
diff --git a/src/plumpy/ports.py b/src/plumpy/ports.py
index 7d782a46..cfbd92d5 100644
--- a/src/plumpy/ports.py
+++ b/src/plumpy/ports.py
@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 """Module for process ports"""
-import abc
+
 import collections
 import copy
 import inspect
@@ -9,7 +9,9 @@
 import warnings
 from typing import Any, Callable, Dict, Iterator, List, Mapping, MutableMapping, Optional, Sequence, Type, Union, cast
 
-from plumpy.utils import is_mutable_property
+from plumpy.utils import AttributesFrozendict, is_mutable_property, type_check
+
+__all__ = ['UNSPECIFIED', 'InputPort', 'OutputPort', 'Port', 'PortNamespace', 'PortValidationError']
 
 _LOGGER = logging.getLogger(__name__)
 UNSPECIFIED = ()
diff --git a/src/plumpy/utils.py b/src/plumpy/utils.py
index d81c936a..f627782f 100644
--- a/src/plumpy/utils.py
+++ b/src/plumpy/utils.py
@@ -135,7 +135,7 @@ def load_function(name: str, instance: Optional[Any] = None) -> Callable[..., An
     obj = load_object(name)
     if inspect.ismethod(obj):
         if instance is not None:
-            return obj.__get__(instance, instance.__class__)
+            return types.MethodType(obj.__func__, instance)
 
         return obj
 
diff --git a/src/plumpy/workchains.py b/src/plumpy/workchains.py
index b97facd4..b48b1c6b 100644
--- a/src/plumpy/workchains.py
+++ b/src/plumpy/workchains.py
@@ -7,7 +7,23 @@
 import inspect
 import logging
 import re
-import six
+from typing import (
+    Any,
+    Callable,
+    Dict,
+    Hashable,
+    List,
+    Mapping,
+    MutableSequence,
+    Optional,
+    Sequence,
+    Tuple,
+    Type,
+    Union,
+    cast,
+)
+
+import kiwipy
 
 from . import lang, mixins, persistence, process_states, processes
 from .utils import PID_TYPE, SAVED_STATE_TYPE
@@ -248,7 +264,7 @@ def __str__(self) -> str:
 class _FunctionCall(_Instruction):
     def __init__(self, func: WC_COMMAND_TYPE) -> None:
         try:
-            args = inspect.getargspec(func)[0]
+            args = inspect.getfullargspec(func)[0]
         except TypeError:
             raise TypeError(f'func is not a function, got {type(func)}')
         if len(args) != 1: